Drug class

201019-N-DA693-1002

Drug classes refer to the categorization of drugs into groups that share similar characteristics. This classification can be based on chemical structure, mechanism of action, mode of action, or therapeutic use. Understanding drug classes is crucial for healthcare professionals to choose the appropriate medication for treating specific conditions and for pharmacologists in drug development.

Comprehensive Systems

Two notable systems that offer a comprehensive classification of drugs include:

• Anatomical Therapeutic Chemical Classification System (ATC): This system combines classification by organ system and therapeutic, pharmacological, and chemical properties. It organizes drugs into five levels, facilitating a global standard for medication classification.
• Systematized Nomenclature of Medicine (SNOMED): SNOMED includes a section devoted to drug classification, providing a detailed categorization from a medical informatics perspective.

Chemical Class

Chemical classification groups drugs by their chemical composition and structure. Examples include:

• Benzodiazepines: Sedatives that work by enhancing the effect of the neurotransmitter GABA.
• Cardiac Glycosides: Increase the force of heart contractions and are used in heart failure.
• Fibrates: Lower blood triglycerides and are used in the prevention and treatment of atherosclerosis.
• Steroids: Include hormones and medications with anti-inflammatory properties.
• Thiazide Diuretics: Lower blood pressure by reducing fluid retention.
• Triptans: Treat migraines by stimulating serotonin receptors.
• β-lactam Antibiotics: Include penicillins and cephalosporins, which kill bacteria by interfering with their cell wall synthesis.

Mechanism of Action

This categorization is based on the biological target a drug modulates. Examples of drug classes defined by mechanism of action include:

• 5-alpha-reductase Inhibitors: Reduce the production of dihydrotestosterone and are used in the treatment of benign prostatic hyperplasia.
• ACE Inhibitors: Lower blood pressure by inhibiting the enzyme that converts angiotensin I to angiotensin II.
• Beta Blockers: Reduce blood pressure and heart rate by blocking beta-adrenergic receptors.
• Proton-pump Inhibitors: Reduce stomach acid production by inhibiting the H+/K+ ATPase enzyme.

Mode of Action

Drugs categorized by mode of action produce a specific functional or anatomical change. Classes include:

• Antifungals: Treat fungal infections by disrupting the cell membrane of fungi.
• Antimicrobials: Include antibiotics, antivirals, and antifungals that kill or inhibit the growth of microorganisms.
• Antithrombotics: Prevent blood clots by inhibiting coagulation or promoting clot breakdown.
• Diuretics: Increase urine production to remove excess fluid from the body.

Therapeutic Class

Therapeutic classification groups drugs by the disease or condition they are used to treat. Examples include:

• Analgesics: Relieve pain without causing unconsciousness.
• Antidepressants: Treat depression by altering neurotransmitter levels in the brain.
• Antidiabetics: Manage diabetes by regulating blood glucose levels.
• Cardiovascular Drugs: Address heart and blood vessel conditions.

Glossary of Terms

• Agonist: A substance that activates a receptor to produce a biological response.
• Antagonist: A substance that blocks the action of an agonist at a receptor.
• Bioavailability: The proportion of a drug that enters circulation when introduced into the body and can have an active effect.
• Enzyme: Proteins that catalyze chemical reactions in the body.
• Pharmacodynamics: The study of the biochemical and physiological effects of drugs and their mechanisms of action.
• Pharmacokinetics: The study of how drugs are absorbed, distributed, metabolized, and excreted by the body.

More drug classes

• 14-alpha Demethylase Inhibitors Compounds that specifically inhibit STEROL 14-DEMETHYLASE. A variety of azole-derived ANTIFUNGAL AGENTS act through this mechanism. 
• 5-alpha Reductase Inhibitors Drugs that inhibit 3-OXO-5-ALPHA-STEROID 4-DEHYDROGENASE. They are commonly used to reduce the production of DIHYDROTESTOSTERONE. 
• Abortifacient Agents, Nonsteroidal Non-steroidal chemical compounds with abortifacient activity. 
• Acaricides A pesticide or chemical agent that kills mites and ticks. This is a large class that includes carbamates, formamides, organochlorines, organophosphates, etc, that act as antibiotics or growth regulators. 
• Acetaldehyde Dehydrogenase Inhibitors Compounds that bind to and inhibit the enzymatic activity of acetaldehyde dehydrogenases. 
• Acid Sensing Ion Channel Blockers A subclass of sodium channel blockers that are specific for ACID-SENSING SODIUM CHANNELS. 
• Adenosine A1 Receptor Antagonists Compounds that bind to and block the stimulation of ADENOSINE A1 RECEPTORS. 
• Adenosine A2 Receptor Agonists Compounds that selectively bind to and activate ADENOSINE A2 RECEPTORS. 
• Adenosine A2 Receptor Antagonists Compounds that selectively bind to and block the activation of ADENOSINE A2 RECEPTORS. 
• Adenosine Diphosphate Receptor Antagonists See Purinergic P2Y Receptor Antagonists
• Adenylyl Cyclase Inhibitors Compounds that bind to and inhibit the action of ADENYLYL CYCLASES. 
• Adjuvants, Anesthesia Agents that are administered in association with anesthetics to increase effectiveness, improve delivery, or decrease required dosage. 
• Adjuvants, Immunologic Substances that augment, stimulate, activate, potentiate, or modulate the immune response at either the cellular or humoral level. The classical agents contain bacterial antigens. Some are endogenous . Their mode of action is either non-specific, resulting in increased immune responsiveness to a wide variety of antigens, or antigen-specific, i.e., affecting a restricted type of immune response to a narrow group of antigens. The therapeutic efficacy of many biological response modifiers is related to their antigen-specific immunoadjuvanticity. 
• Adjuvants, Pharmaceutic Agents that aid or increase the action of the principle drug or that affect the absorption, mechanism of action, metabolism, or excretion of the primary drug in such a way as to enhance its effects. 
• Adrenergic Agents Drugs that act on adrenergic receptors or affect the life cycle of adrenergic transmitters. Included here are adrenergic agonists and antagonists and agents that affect the synthesis, storage, uptake, metabolism, or release of adrenergic transmitters. 
• Adrenergic Antagonists Drugs that bind to but do not activate ADRENERGIC RECEPTORS. Adrenergic antagonists block the actions of the endogenous adrenergic transmitters EPINEPHRINE and NOREPINEPHRINE. 
• Adrenergic Uptake Inhibitors Drugs that block the transport of adrenergic transmitters into axon terminals or into storage vesicles within terminals. The tricyclic antidepressants and amphetamines are among the therapeutically important drugs that may act via inhibition of adrenergic transport. Many of these drugs also block transport of serotonin. 
• Adrenergic alpha-1 Receptor Agonists Compounds that bind to and activate ADRENERGIC ALPHA-1 RECEPTORS. 
• Adrenergic alpha-1 Receptor Antagonists Drugs that bind to and block the activation of ADRENERGIC ALPHA-1 RECEPTORS. 
• Adrenergic alpha-2 Receptor Agonists Compounds that bind to and activate ADRENERGIC ALPHA-2 RECEPTORS. 
• Adrenergic alpha-2 Receptor Antagonists Drugs that bind to and block the activation of ADRENERGIC ALPHA-2 RECEPTORS. 
• Adrenergic alpha-Agonists Drugs that selectively bind to and activate alpha adrenergic receptors. 
• Adrenergic alpha-Antagonists Drugs that bind to but do not activate alpha-adrenergic receptors thereby blocking the actions of endogenous or exogenous adrenergic agonists. Adrenergic alpha-antagonists are used in the treatment of hypertension, vasospasm, peripheral vascular disease, shock, and pheochromocytoma. 
• Adrenergic beta-1 Receptor Agonists Compounds that bind to and activate ADRENERGIC BETA-1 RECEPTORS. 
• Adrenergic beta-1 Receptor Antagonists Drugs that bind to and block the activation of ADRENERGIC BETA-1 RECEPTORS. 
• Adrenergic beta-2 Receptor Agonists Compounds bind to and activate ADRENERGIC BETA-2 RECEPTORS. 
• Adrenergic beta-2 Receptor Antagonists Drugs that bind to and block the activation of ADRENERGIC BETA-2 RECEPTORS. 
• Adrenergic beta-3 Receptor Agonists Compounds that bind to and activate ADRENERGIC BETA-3 RECEPTORS. 
• Adrenergic beta-Agonists Drugs that selectively bind to and activate beta-adrenergic receptors. 
• Adrenergic beta-Antagonists Drugs that bind to but do not activate beta-adrenergic receptors thereby blocking the actions of beta-adrenergic agonists. Adrenergic beta-antagonists are used for treatment of hypertension, cardiac arrhythmias, angina pectoris, glaucoma, migraine headaches, and anxiety. 
• Aerosol Propellants Compressed gases or vapors in a container which, upon release of pressure and expansion through a valve, carry another substance from the container. They are used for cosmetics, household cleaners, and so on. Examples are BUTANES; CARBON DIOXIDE; FLUOROCARBONS; NITROGEN; and PROPANE.  
• Affinity Labels Analogs of those substrates or compounds which bind naturally at the active sites of proteins, enzymes, antibodies, steroids, or physiological receptors. These analogs form a stable covalent bond at the binding site, thereby acting as inhibitors of the proteins or steroids. 
• Air Pollutants, Occupational Air pollutants found in the work area. They are usually produced by the specific nature of the occupation. 
• Air Pollutants, Radioactive Pollutants, present in air, which exhibit radioactivity. 
• Air Pollutants Any substance in the air which could, if present in high enough concentration, harm humans, animals, vegetation or material. Substances include GASES; PARTICULATE MATTER; and volatile ORGANIC CHEMICALS. 
• Alcohol Deterrents Substances interfering with the metabolism of ethyl alcohol, causing unpleasant side effects thought to discourage the drinking of alcoholic beverages. Alcohol deterrents are used in the treatment of alcoholism. 
• Alkylating Agents Highly reactive chemicals that introduce alkyl radicals into biologically active molecules and thereby prevent their proper functioning. Many are used as antineoplastic agents, but most are very toxic, with carcinogenic, mutagenic, teratogenic, and immunosuppressant actions. They have also been used as components in poison gases. 
• Amebicides Agents which are destructive to amebae, especially the parasitic species causing AMEBIASIS in man and animal. 
• Amylin Receptor Agonists Compounds that stimulate the activity of AMYMIN RECEPTORS. Included under this heading is the endogenous form of ISLET AMYLOID POLYPEPTIDE and synthetic compounds that mimic its effect. 
• Anabolic Agents These compounds stimulate anabolism and inhibit catabolism. They stimulate the development of muscle mass, strength, and power. 
• Analgesics, Non-Narcotic A subclass of analgesic agents that typically do not bind to OPIOID RECEPTORS and are not addictive. Many non-narcotic analgesics are offered as NONPRESCRIPTION DRUGS. 
• Analgesics, Opioid Compounds with activity like OPIATE ALKALOIDS, acting at OPIOID RECEPTORS. Properties include induction of ANALGESIA or NARCOSIS. 
• Androgen Antagonists Compounds which inhibit or antagonize the biosynthesis or actions of androgens. 
• Androgens Compounds that interact with ANDROGEN RECEPTORS in target tissues to bring about the effects similar to those of TESTOSTERONE. Depending on the target tissues, androgenic effects can be on SEX DIFFERENTIATION; male reproductive organs, SPERMATOGENESIS; secondary male SEX CHARACTERISTICS; LIBIDO; development of muscle mass, strength, and power. 
• Anesthetics, Combined The use of two or more chemicals simultaneously or sequentially to induce anesthesia. The drugs need not be in the same dosage form. 
• Anesthetics, Dissociative Intravenous anesthetics that induce a state of sedation, immobility, amnesia, and marked analgesia. Subjects may experience a strong feeling of dissociation from the environment. The condition produced is similar to NEUROLEPTANALGESIA, but is brought about by the administration of a single drug.  
• Anesthetics, Inhalation Gases or volatile liquids that vary in the rate at which they induce anesthesia; potency; the degree of circulation, respiratory, or neuromuscular depression they produce; and analgesic effects. Inhalation anesthetics have advantages over intravenous agents in that the depth of anesthesia can be changed rapidly by altering the inhaled concentration. Because of their rapid elimination, any postoperative respiratory depression is of relatively short duration.  
• Anesthetics, Intravenous Ultrashort-acting anesthetics that are used for induction. Loss of consciousness is rapid and induction is pleasant, but there is no muscle relaxation and reflexes frequently are not reduced adequately. Repeated administration results in accumulation and prolongs the recovery time. Since these agents have little if any analgesic activity, they are seldom used alone except in brief minor procedures.  
• Anesthetics, Local Drugs that block nerve conduction when applied locally to nerve tissue in appropriate concentrations. They act on any part of the nervous system and on every type of nerve fiber. In contact with a nerve trunk, these anesthetics can cause both sensory and motor paralysis in the innervated area. Their action is completely reversible. Nearly all local anesthetics act by reducing the tendency of voltage-dependent sodium channels to activate. 
• Anesthetics Agents that are capable of inducing a total or partial loss of sensation, especially tactile sensation and pain. They may act to induce general ANESTHESIA, in which an unconscious state is achieved, or may act locally to induce numbness or lack of sensation at a targeted site. 
• Angiogenesis Inhibitors Agents and endogenous substances that antagonize or inhibit the development of new blood vessels. 
• Angiotensin II Type 1 Receptor Blockers Agents that antagonize ANGIOTENSIN II TYPE 1 RECEPTOR. Included are ANGIOTENSIN II analogs such as SARALASIN and biphenylimidazoles such as LOSARTAN. Some are used as ANTIHYPERTENSIVE AGENTS. 
• Angiotensin II Type 2 Receptor Blockers Agents that antagonize the ANGIOTENSIN II TYPE 2 RECEPTOR. 
• Angiotensin-Converting Enzyme Inhibitors A class of drugs whose main indications are the treatment of hypertension and heart failure. They exert their hemodynamic effect mainly by inhibiting the renin-angiotensin system. They also modulate sympathetic nervous system activity and increase prostaglandin synthesis. They cause mainly vasodilation and mild natriuresis without affecting heart rate and contractility. 
• Anion Exchange Resins High-molecular-weight insoluble polymers that contain functional cationic groups capable of undergoing exchange reactions with anions. 
• Antacids Substances that counteract or neutralize acidity of the GASTROINTESTINAL TRACT. 
• Anthelmintics Agents destructive to parasitic worms. They are used therapeutically in the treatment of HELMINTHIASIS in man and animal. 
• Anti-Allergic Agents Agents that are used to treat allergic reactions. Most of these drugs act by preventing the release of inflammatory mediators or inhibiting the actions of released mediators on their target cells.  
• Anti-Anxiety Agents Agents that alleviate ANXIETY, tension, and ANXIETY DISORDERS, promote sedation, and have a calming effect without affecting clarity of consciousness or neurologic conditions. ADRENERGIC BETA-ANTAGONISTS are commonly used in the symptomatic treatment of anxiety but are not included here. 
• Anti-Arrhythmia Agents Agents used for the treatment or prevention of cardiac arrhythmias. They may affect the polarization-repolarization phase of the action potential, its excitability or refractoriness, or impulse conduction or membrane responsiveness within cardiac fibers. Anti-arrhythmia agents are often classed into four main groups according to their mechanism of action: sodium channel blockade, beta-adrenergic blockade, repolarization prolongation, or calcium channel blockade. 
• Anti-Bacterial Agents Substances that reduce the growth or reproduction of BACTERIA. 
• Anti-Dyskinesia Agents Drugs used in the treatment of movement disorders. Most of these act centrally on dopaminergic or cholinergic systems. Among the most important clinically are those used for the treatment of Parkinson disease and those for the tardive dyskinesias. 
• Anti-HIV Agents Agents used to treat AIDS and/or stop the spread of the HIV infection. These do not include drugs used to treat symptoms or opportunistic infections associated with AIDS. 
• Anti-Infective Agents, Local Substances used on humans and other animals that destroy harmful microorganisms or inhibit their activity. They are distinguished from DISINFECTANTS, which are used on inanimate objects. 
• Anti-Infective Agents, Urinary Substances capable of killing agents causing urinary tract infections or of preventing them from spreading. 
• Anti-Infective Agents Substances that prevent infectious agents or organisms from spreading or kill infectious agents in order to prevent the spread of infection. 
• Anti-Inflammatory Agents, Non-Steroidal Anti-inflammatory agents that are non-steroidal in nature. In addition to anti-inflammatory actions, they have analgesic, antipyretic, and platelet-inhibitory actions.They act by blocking the synthesis of prostaglandins by inhibiting cyclooxygenase, which converts arachidonic acid to cyclic endoperoxides, precursors of prostaglandins. Inhibition of prostaglandin synthesis accounts for their analgesic, antipyretic, and platelet-inhibitory actions; other mechanisms may contribute to their anti-inflammatory effects. 
• Anti-Obesity Agents Agents that increase energy expenditure and weight loss by neural and chemical regulation. Beta-adrenergic agents and serotoninergic drugs have been experimentally used in patients with non-insulin dependent diabetes mellitus to treat obesity. 
• Anti-Ulcer Agents Various agents with different action mechanisms used to treat or ameliorate PEPTIC ULCER or irritation of the gastrointestinal tract. This has included ANTIBIOTICS to treat HELICOBACTER INFECTIONS; HISTAMINE H2 ANTAGONISTS to reduce GASTRIC ACID secretion; and ANTACIDS for symptomatic relief. 
• Antibiotics, Antineoplastic Chemical substances, produced by microorganisms, inhibiting or preventing the proliferation of neoplasms. 
• Antibiotics, Antitubercular Substances obtained from various species of microorganisms that are, alone or in combination with other agents, of use in treating various forms of tuberculosis; most of these agents are merely bacteriostatic, induce resistance in the organisms, and may be toxic. 
• Anticarcinogenic Agents Agents that reduce the frequency or rate of spontaneous or induced tumors independently of the mechanism involved. 
• Antidepressive Agents, Second-Generation A structurally and mechanistically diverse group of drugs that are not tricyclics or monoamine oxidase inhibitors. The most clinically important appear to act selectively on serotonergic systems, especially by inhibiting serotonin reuptake. 
• Antidepressive Agents, Tricyclic Substances that contain a fused three-ring moiety and are used in the treatment of depression. These drugs block the uptake of norepinephrine and serotonin into axon terminals and may block some subtypes of serotonin, adrenergic, and histamine receptors. However the mechanism of their antidepressant effects is not clear because the therapeutic effects usually take weeks to develop and may reflect compensatory changes in the central nervous system. 
• Antidepressive Agents Mood-stimulating drugs used primarily in the treatment of affective disorders and related conditions. Several MONOAMINE OXIDASE INHIBITORS are useful as antidepressants apparently as a long-term consequence of their modulation of catecholamine levels. The tricyclic compounds useful as antidepressive agents also appear to act through brain catecholamine systems. A third group is a diverse group of drugs including some that act specifically on serotonergic systems. 
• Antidiarrheals Miscellaneous agents found useful in the symptomatic treatment of diarrhea. They have no effect on the agent that cause diarrhea, but merely alleviate the condition. 
• Antidiuretic Agents Agents that reduce the excretion of URINE, most notably the octapeptide VASOPRESSINS. 
• Antidiuretic Hormone Receptor Antagonists Endogenous compounds and drugs that inhibit or block the activity of ANTIDUIRETIC HORMONE RECEPTORS. 
• Antifibrinolytic Agents Agents that prevent fibrinolysis or lysis of a blood clot or thrombus. Several endogenous antiplasmins are known. The drugs are used to control massive hemorrhage and in other coagulation disorders. 
• Antifoaming Agents Agents used to prevent the formation of foam or to treat flatulence or bloat. 
• Antifungal Agents Substances that destroy fungi by suppressing their ability to grow or reproduce. They differ from FUNGICIDES, INDUSTRIAL because they defend against fungi present in human or animal tissues. 
• Antihypertensive Agents Drugs used in the treatment of acute or chronic vascular HYPERTENSION regardless of pharmacological mechanism. Among the antihypertensive agents are DIURETICS; ; ADRENERGIC BETA-ANTAGONISTS; ADRENERGIC ALPHA-ANTAGONISTS; ANGIOTENSIN-CONVERTING ENZYME INHIBITORS; CALCIUM CHANNEL BLOCKERS; GANGLIONIC BLOCKERS; and VASODILATOR AGENTS. 
• Antimalarials Agents used in the treatment of malaria. They are usually classified on the basis of their action against plasmodia at different stages in their life cycle in the human.  
• Antimanic Agents Agents that are used to treat bipolar disorders or mania associated with other affective disorders. 
• Antimetabolites, Antineoplastic Antimetabolites that are useful in cancer chemotherapy. 
• Antimetabolites Drugs that are chemically similar to naturally occurring metabolites, but differ enough to interfere with normal metabolic pathways.  
• Antimitotic Agents Agents that arrest cells in MITOSIS, most notably TUBULIN MODULATORS. 
• Antimutagenic Agents Agents that reduce the frequency or rate of spontaneous or induced mutations independently of the mechanism involved. 
• Antinematodal Agents Substances used in the treatment or control of nematode infestations. They are used also in veterinary practice. 
• Antineoplastic Agents, Alkylating A class of drugs that differs from other alkylating agents used clinically in that they are monofunctional and thus unable to cross-link cellular macromolecules. Among their common properties are a requirement for metabolic activation to intermediates with antitumor efficacy and the presence in their chemical structures of N-methyl groups, that after metabolism, can covalently modify cellular DNA. The precise mechanisms by which each of these drugs acts to kill tumor cells are not completely understood.  
• Antineoplastic Agents, Hormonal Antineoplastic agents that are used to treat hormone-sensitive tumors. Hormone-sensitive tumors may be hormone-dependent, hormone-responsive, or both. A hormone-dependent tumor regresses on removal of the hormonal stimulus, by surgery or pharmacological block. Hormone-responsive tumors may regress when pharmacologic amounts of hormones are administered regardless of whether previous signs of hormone sensitivity were observed. The major hormone-responsive cancers include carcinomas of the breast, prostate, and endometrium; lymphomas; and certain leukemias.  
• Antineoplastic Agents, Phytogenic Agents obtained from higher plants that have demonstrable cytostatic or antineoplastic activity. 
• Antineoplastic Agents Substances that inhibit or prevent the proliferation of NEOPLASMS. 
• Antioxidants Naturally occurring or synthetic substances that inhibit or retard the oxidation of a substance to which it is added. They counteract the harmful and damaging effects of oxidation in animal tissues. 
• Antiparkinson Agents Agents used in the treatment of Parkinson's disease. The most commonly used drugs act on the dopaminergic system in the striatum and basal ganglia or are centrally acting muscarinic antagonists. 
• Antiperspirants Agents that are put on the SKIN to reduce SWEATING or prevent excess sweating . 
• Antiplatyhelmintic Agents Agents used to treat cestode, trematode, or other flatworm infestations in man or animals. 
• Antipsychotic Agents Agents that control agitated psychotic behavior, alleviate acute psychotic states, reduce psychotic symptoms, and exert a quieting effect. They are used in SCHIZOPHRENIA; senile dementia; transient psychosis following surgery; or MYOCARDIAL INFARCTION; etc. These drugs are often referred to as neuroleptics alluding to the tendency to produce neurological side effects, but not all antipsychotics are likely to produce such effects. Many of these drugs may also be effective against nausea, emesis, and pruritus. 
• Antisickling Agents Agents used to prevent or reverse the pathological events leading to sickling of erythrocytes in sickle cell conditions. 
• Antispermatogenic Agents Agents, either mechanical or chemical, which destroy spermatozoa in the male genitalia and block spermatogenesis. 
• Antithrombins Endogenous factors and drugs that directly inhibit the action of THROMBIN, usually by blocking its enzymatic activity. They are distinguished from INDIRECT THROMBIN INHIBITORS, such as HEPARIN, which act by enhancing the inhibitory effects of antithrombins. 
• Antithyroid Agents Agents that are used to treat hyperthyroidism by reducing the excessive production of thyroid hormones. 
• Antitreponemal Agents Agents used to treat infections with bacteria of the genus TREPONEMA. This includes SYPHILIS & YAWS. 
• Antitubercular Agents Drugs used in the treatment of tuberculosis. They are divided into two main classes: "first-line" agents, those with the greatest efficacy and acceptable degrees of toxicity used successfully in the great majority of cases; and "second-line" drugs used in drug-resistant cases or those in which some other patient-related condition has compromised the effectiveness of primary therapy. 
• Antitussive Agents Agents that suppress cough. They act centrally on the medullary cough center. EXPECTORANTS, also used in the treatment of cough, act locally. 
• Antiviral Agents Agents used in the prophylaxis or therapy of VIRUS DISEASES. Some of the ways they may act include preventing viral replication by inhibiting viral DNA polymerase; binding to specific cell-surface receptors and inhibiting viral penetration or uncoating; inhibiting viral protein synthesis; or blocking late stages of virus assembly. 
• Appetite Stimulants Agents that are used to stimulate appetite. These drugs are frequently used to treat anorexia associated with cancer and AIDS. 
• Aromatase Inhibitors Compounds that inhibit AROMATASE in order to reduce production of estrogenic steroid hormones. 
• Aromatic Amino Acid Decarboxylase Inhibitors Compounds and drugs that block or inhibit the enzymatic action of AROMATIC AMINO ACID DECARBOXYLASES. Pharmaceutical agents in this category are used in conjunction with LEVODOPA in order to slow its metabolism. 
• Astringents Agents, usually topical, that cause the contraction of tissues for the control of bleeding or secretions. 
• Beta-Lactamase Inhibitors Endogenous substances and drugs that inhibit or block the activity of BETA-LACTAMASES. 
• Biocompatible Materials Synthetic or natural materials, other than DRUGS, that are used to replace or repair any body TISSUES or bodily function. 
• Bone Cements Adhesives used to fix prosthetic devices to bones and to cement bone to bone in difficult fractures. Synthetic resins are commonly used as cements. A mixture of monocalcium phosphate, monohydrate, alpha-tricalcium phosphate, and calcium carbonate with a sodium phosphate solution is also a useful bone paste. 
• Bone Density Conservation Agents Agents that inhibit BONE RESORPTION and/or favor BONE MINERALIZATION and BONE REGENERATION. They are used to heal BONE FRACTURES and to treat METABOLIC BONE DISEASES such as OSTEOPOROSIS. 
• Bradykinin B2 Receptor Antagonists Compounds and drugs that inhibit ligand binding or cellular signaling by BRADYKININ B2 RECEPTORS. 
• Bradykinin Receptor Antagonists Compounds and drugs that inhibit ligand binding or cellular signaling by BRADYKININ RECEPTORS. 
• Bronchoconstrictor Agents Agents causing the narrowing of the lumen of a bronchus or bronchiole. 
• Bronchodilator Agents Agents that cause an increase in the expansion of a bronchus or bronchial tubes. 
• CCR5 Receptor Antagonists Compounds and drugs that inhibit or block the activity of CCR5 RECEPTORS. 
• Calcimimetic Agents Small organic molecules that act as allosteric activators of the calcium sensing receptor in the PARATHYROID GLANDS and other tissues. They lower the threshold for CaSR activation by extracellular calcium ions and diminish PARATHYROID HORMONE release from parathyroid cells. 
• Calcineurin Inhibitors Compounds that inhibit or block the PHOSPHATASE activity of CALCINEURIN. 
• Calcium Channel Agonists Agents that increase calcium influx into calcium channels of excitable tissues. This causes vasoconstriction in VASCULAR SMOOTH MUSCLE and/or CARDIAC MUSCLE cells as well as stimulation of insulin release from pancreatic islets. Therefore, tissue-selective calcium agonists have the potential to combat cardiac failure and endocrinological disorders. They have been used primarily in experimental studies in cell and tissue culture. 
• Calcium Channel Blockers A class of drugs that act by selective inhibition of calcium influx through cellular membranes. 
• Calcium Ionophores Chemical agents that increase the permeability of CELL MEMBRANES to CALCIUM ions. 
• Cannabinoid Receptor Agonists Compounds that interact with and stimulate the activity of CANNABINOID RECEPTORS. 
• Cannabinoid Receptor Antagonists Compounds that inhibit or block the activity of CANNABINOID RECEPTORS. 
• Carbonic Anhydrase Inhibitors A class of compounds that reduces the secretion of H+ ions by the proximal kidney tubule through inhibition of CARBONIC ANHYDRASES. 
• Carcinogens, Environmental Carcinogenic substances that are found in the environment. 
• Carcinogens Substances that increase the risk of NEOPLASMS in humans or animals. Both genotoxic chemicals, which affect DNA directly, and nongenotoxic chemicals, which induce neoplasms by other mechanism, are included. 
• Cardiotonic Agents Agents that have a strengthening effect on the heart or that can increase cardiac output. They may be CARDIAC GLYCOSIDES; SYMPATHOMIMETICS; or other drugs. They are used after MYOCARDIAL INFARCT; CARDIAC SURGICAL PROCEDURES; in SHOCK; or in congestive heart failure . 
• Cardiovascular Agents Agents that affect the rate or intensity of cardiac contraction, blood vessel diameter, or blood volume. 
• Catechol O-Methyltransferase Inhibitors Compounds and drugs that inhibit or block the activity of CATECHOL O-METHYLTRANSFERASE enzymes. Drugs in this class are used in management of central nervous system disorders such as PARKINSON DISEASE. 
• Cation Exchange Resins High molecular weight insoluble polymers which contain functional anionic groups that are capable of undergoing exchange reactions with cations. 
• Caustics Strong alkaline chemicals that destroy soft body tissues resulting in a deep, penetrating type of burn, in contrast to corrosives, that result in a more superficial type of damage via chemical means or inflammation. Caustics are usually hydroxides of light metals. SODIUM HYDROXIDE and potassium hydroxide are the most widely used caustic agents in industry. Medically, they have been used externally to remove diseased or dead tissues and destroy warts and small tumors. The accidental ingestion of products containing caustic ingredients results in thousands of injuries per year. 
• Central Nervous System Depressants A very loosely defined group of drugs that tend to reduce the activity of the central nervous system. The major groups included here are ethyl alcohol, anesthetics, hypnotics and sedatives, narcotics, and tranquilizing agents . 
• Central Nervous System Stimulants A loosely defined group of drugs that tend to increase behavioral alertness, agitation, or excitation. They work by a variety of mechanisms, but usually not by direct excitation of neurons. The many drugs that have such actions as side effects to their main therapeutic use are not included here. 
• Chelating Agents Chemicals that bind to and remove ions from solutions. Many chelating agents function through the formation of COORDINATION COMPLEXES with METALS. 
• Chemical Warfare Agents Chemicals that are used to cause the disturbance, disease, or death of humans during WARFARE. 
• Chemosterilants Compounds that cause reproductive sterility in organisms. They are sometimes used to control pest populations by sterilizing males within the population. 
• Cholagogues and Choleretics Gastrointestinal agents that stimulate the flow of bile into the duodenum or stimulate the production of bile by the liver . 
• Cholinergic Agents Any drug used for its actions on cholinergic systems. Included here are agonists and antagonists, drugs that affect the life cycle of ACETYLCHOLINE, and drugs that affect the survival of cholinergic neurons. The term cholinergic agents is sometimes still used in the narrower sense of MUSCARINIC AGONISTS, although most modern texts discourage that usage. 
• Cholinergic Antagonists Drugs that bind to but do not activate CHOLINERGIC RECEPTORS, thereby blocking the actions of ACETYLCHOLINE or cholinergic agonists. 
• Cholinesterase Inhibitors Drugs that inhibit cholinesterases. The neurotransmitter ACETYLCHOLINE is rapidly hydrolyzed, and thereby inactivated, by cholinesterases. When cholinesterases are inhibited, the action of endogenously released acetylcholine at cholinergic synapses is potentiated. Cholinesterase inhibitors are widely used clinically for their potentiation of cholinergic inputs to the gastrointestinal tract and urinary bladder, the eye, and skeletal muscles; they are also used for their effects on the heart and the central nervous system. 
• Cholinesterase Reactivators Drugs used to reverse the inactivation of cholinesterase caused by organophosphates or sulfonates. They are an important component of therapy in agricultural, industrial, and military poisonings by organophosphates and sulfonates. 
• Chromogenic Compounds Colorless, endogenous or exogenous pigment precursors that may be transformed by biological mechanisms into colored compounds; used in biochemical assays and in diagnosis as indicators, especially in the form of enzyme substrates. Synonym: chromogens . 
• Coccidiostats Agents useful in the treatment or prevention of COCCIDIOSIS in man or animals. 
• Coloring Agents Chemicals and substances that impart color including soluble dyes and insoluble pigments. They are used in INKS; PAINTS; and as INDICATORS AND REAGENTS. 
• Complement Inactivating Agents Compounds that negatively regulate the cascade process of COMPLEMENT ACTIVATION. Uncontrolled complement activation and resulting cell lysis is potentially dangerous for the host. 
• Contraceptive Agents, Female Chemical substances or agents with contraceptive activity in females. Use for female contraceptive agents in general or for which there is no specific heading. 
• Contraceptive Agents, Male Chemical substances or agents with contraceptive activity in males. Use for male contraceptive agents in general or for which there is no specific heading. 
• Contraceptive Agents Chemical substances that prevent or reduce the probability of CONCEPTION. 
• Contraceptives, Oral, Combined Fixed drug combinations administered orally for contraceptive purposes. 
• Contraceptives, Oral, Hormonal Oral contraceptives which owe their effectiveness to hormonal preparations. 
• Contraceptives, Oral, Sequential Drugs administered orally and sequentially for contraceptive purposes. 
• Contraceptives, Oral, Synthetic Oral contraceptives which owe their effectiveness to synthetic preparations. 
• Contraceptives, Oral Compounds, usually hormonal, taken orally in order to block ovulation and prevent the occurrence of pregnancy. The hormones are generally estrogen or progesterone or both. 
• Contraceptives, Postcoital, Hormonal Postcoital contraceptives which owe their effectiveness to hormonal preparations. 
• Contraceptives, Postcoital, Synthetic Postcoital contraceptives which owe their effectiveness to synthetic preparations. 
• Contraceptives, Postcoital Contraceptive substances to be used after COITUS. These agents include high doses of estrogenic drugs; progesterone-receptor blockers; ANTIMETABOLITES; ALKALOIDS, and PROSTAGLANDINS. 
• Convulsants Substances that act in the brain stem or spinal cord to produce tonic or clonic convulsions, often by removing normal inhibitory tone. They were formerly used to stimulate respiration or as antidotes to barbiturate overdose. They are now most commonly used as experimental tools. 
• Cosmetics Substances intended to be applied to the human body for cleansing, beautifying, promoting attractiveness, or altering the appearance without affecting the body's structure or functions. Included in this definition are skin creams, lotions, perfumes, lipsticks, fingernail polishes, eye and facial makeup preparations, permanent waves, hair colors, toothpastes, and deodorants, as well as any material intended for use as a component of a cosmetic product. Feb 1995)--> 
• Cross-Linking Reagents Reagents with two reactive groups, usually at opposite ends of the molecule, that are capable of reacting with and thereby forming bridges between side chains of amino acids in proteins; the locations of naturally reactive areas within proteins can thereby be identified; may also be used for other macromolecules, like glycoproteins, nucleic acids, or other. 
• Cryoprotective Agents Substances that provide protection against the harmful effects of freezing temperatures. 
• Culture Media Any liquid or solid preparation made specifically for the growth, storage, or transport of microorganisms or other types of cells. The variety of media that exist allow for the culturing of specific microorganisms and cell types, such as differential media, selective media, test media, and defined media. Solid media consist of liquid media that have been solidified with an agent such as AGAR or GELATIN. 
• Cyclooxygenase 2 Inhibitors A subclass of cyclooxygenase inhibitors with specificity for CYCLOOXYGENASE-2. 
• Cyclooxygenase Inhibitors Compounds or agents that combine with cyclooxygenase and thereby prevent its substrate-enzyme combination with arachidonic acid and the formation of eicosanoids, prostaglandins, and thromboxanes. 
• Cysteine Proteinase Inhibitors Exogenous and endogenous compounds which inhibit CYSTEINE ENDOPEPTIDASES. 
• Cystine Depleting Agents Compounds and drugs that react with CYSTINE and convert it into a compound that can be more easily metabolized or intracellularly transported. Drugs in this class have been used to treat CYSTINOSIS. 
• Cytochrome P-450 CYP1A2 Inducers Drugs and compounds that induce the synthesis of CYTOCHROME P-450 CYP1A2. 
• Cytochrome P-450 CYP1A2 Inhibitors Drugs and compounds which inhibit or antagonize the biosynthesis or actions of CYTOCHROME P-450 CYP1A2. 
• Cytochrome P-450 CYP2B6 Inducers Drugs and compounds that induce the synthesis of CYTOCHROME P-450 CYP2B6. 
• Cytochrome P-450 CYP2B6 Inhibitors Drugs and compounds which inhibit or antagonize the biosynthesis or actions of CYTOCHROME P-450 CYP2B6. 
• Cytochrome P-450 CYP2C19 Inducers Drugs and compounds that induce the synthesis of CYTOCHROME P-450 CYP2C19. 
• Cytochrome P-450 CYP2C19 Inhibitors Drugs and compounds which inhibit or antagonize the biosynthesis or actions of CYTOCHROME P-450 CYP2C19. 
• Cytochrome P-450 CYP2C8 Inducers Drugs and compounds that induce the synthesis of CYTOCHROME P-450 CYP2C8. 
• Cytochrome P-450 CYP2C8 Inhibitors Drugs and compounds which inhibit or antagonize the biosynthesis or actions of CYTOCHROME P-450 CYP2C8. 
• Cytochrome P-450 CYP2C9 Inducers Drugs and compounds that induce the synthesis of CYTOCHROME P-450 CYP2C9. 
• Cytochrome P-450 CYP2C9 Inhibitors Drugs and compounds which inhibit or antagonize the biosynthesis or actions of CYTOCHROME P-450 CYP2C9. 
• Cytochrome P-450 CYP2D6 Inhibitors Drugs and compounds which inhibit or antagonize the biosynthesis or actions of CYTOCHROME P-450 CYP2D6. 
• Cytochrome P-450 CYP3A Inducers Drugs and compounds that induce the synthesis of CYTOCHROME P-450 CYP3A. 
• Cytochrome P-450 CYP3A Inhibitors Drugs and compounds which inhibit or antagonize the biosynthesis or actions of CYTOCHROME P-450 CYP3A. 
• Cytochrome P-450 Enzyme Inhibitors Drugs and compounds which inhibit or antagonize the biosynthesis or actions of CYTOCHROME P-450 ENZYMES. 
• Defoliants, Chemical Herbicides that remove leaves from trees and growing plants. They may be either organic or inorganic. Several of the more persistent types have been used in military operations and many are toxic.  
• Delayed-Action Preparations Dosage forms of a drug that act over a period of time by controlled-release processes or technology. 
• Dental Disinfectants Chemicals especially for use on instruments to destroy pathogenic organisms.  
• Dental Materials Materials used in the production of dental bases, restorations, impressions, prostheses, etc. 
• Dentifrices Any preparations used for cleansing teeth; they usually contain an abrasive, detergent, binder and flavoring agent and may exist in the form of liquid, paste or powder; may also contain medicaments and caries preventives. 
• Dermatologic Agents Drugs used to treat or prevent skin disorders or for the routine care of skin. 
• Detergents Purifying or cleansing agents, usually salts of long-chain aliphatic bases or acids, that exert cleansing and antimicrobial effects through a surface action that depends on possessing both hydrophilic and hydrophobic properties. 
• Dipeptidyl-Peptidase IV Inhibitors Compounds that suppress the degradation of INCRETINS by blocking the action of DIPEPTIDYL-PEPTIDASE IV. This helps to correct the defective INSULIN and GLUCAGON secretion characteristic of TYPE 2 DIABETES MELLITUS by stimulating insulin secretion and suppressing glucagon release. 
• Disinfectants Substances used on inanimate objects that destroy harmful microorganisms or inhibit their activity. Disinfectants are classed as complete, destroying SPORES as well as vegetative forms of microorganisms, or incomplete, destroying only vegetative forms of the organisms. They are distinguished from ANTISEPTICS, which are local anti-infective agents used on humans and other animals.  
• Diuretics, Osmotic Compounds that increase urine volume by increasing the amount of osmotically active solute in the urine. Osmotic diuretics also increase the osmolarity of plasma. 
• Diuretics Agents that promote the excretion of urine through their effects on kidney function. 
• Dopamine Agents Any drugs that are used for their effects on dopamine receptors, on the life cycle of dopamine, or on the survival of dopaminergic neurons. 
• Dopamine Antagonists Drugs that bind to but do not activate DOPAMINE RECEPTORS, thereby blocking the actions of dopamine or exogenous agonists. Many drugs used in the treatment of psychotic disorders are dopamine antagonists, although their therapeutic effects may be due to long-term adjustments of the brain rather than to the acute effects of blocking dopamine receptors. Dopamine antagonists have been used for several other clinical purposes including as ANTIEMETICS, in the treatment of Tourette syndrome, and for hiccup. Dopamine receptor blockade is associated with NEUROLEPTIC MALIGNANT SYNDROME. 
• Dopamine D2 Receptor Antagonists Compounds and drugs that bind to and inhibit or block the activation of DOPAMINE D2 RECEPTORS. 
• Dopamine Uptake Inhibitors Drugs that block the transport of DOPAMINE into axon terminals or into storage vesicles within terminals. Most of the ADRENERGIC UPTAKE INHIBITORS also inhibit dopamine uptake. 
• Emetics Agents that cause vomiting. They may act directly on the gastrointestinal tract, bringing about emesis through local irritant effects, or indirectly, through their effects on the chemoreceptor trigger zone in the postremal area near the medulla. 
• Emollients Oleagenous substances used topically to soothe, soften or protect skin or mucous membranes. They are used also as vehicles for other dermatologic agents. 
• Endothelin Receptor Antagonists Compounds and drugs that bind to and inhibit or block the activation of ENDOTHELIN RECECPTORS. 
• Endothelium-Dependent Relaxing Factors Paracrine substances produced by the VASCULAR ENDOTHELIUM with VASCULAR SMOOTH MUSCLE relaxation activities. Several factors have been identified, including NITRIC OXIDE and PROSTACYCLIN. 
• Environmental Pollutants Substances or energies, for example heat or light, which when introduced into the air, water, or land threaten life or health of individuals or ECOSYSTEMS. 
• Enzyme Activators Compounds or factors that act on a specific enzyme to increase its activity. 
• Enzyme Inhibitors Compounds or agents that combine with an enzyme in such a manner as to prevent the normal substrate-enzyme combination and the catalytic reaction. 
• Epithelial Sodium Channel Blockers A subclass of sodium channel blockers that are specific for EPITHELIAL SODIUM CHANNELS. 
• Estrogen Antagonists Compounds which inhibit or antagonize the action or biosynthesis of estrogenic compounds. 
• Estrogen Receptor Antagonists Compounds and drugs that bind to and block or inhibit the activation of ESTROGEN RECEPTORS. 
• Estrogen Receptor Modulators Substances that possess antiestrogenic actions but can also produce estrogenic effects as well. They act as complete or partial agonist or as antagonist. They can be either steroidal or nonsteroidal in structure. 
• Estrogens Compounds that interact with ESTROGEN RECEPTORS in target tissues to bring about the effects similar to those of ESTRADIOL. Estrogens stimulate the female reproductive organs, and the development of secondary female SEX CHARACTERISTICS. Estrogenic chemicals include natural, synthetic, steroidal, or non-steroidal compounds. 
• Excipients Usually inert substances added to a prescription in order to provide suitable consistency to the dosage form. These include binders, matrix, base or diluent in pills, tablets, creams, salves, etc. 
• Excitatory Amino Acid Agonists Drugs that bind to and activate excitatory amino acid receptors. 
• Excitatory Amino Acid Antagonists Drugs that bind to but do not activate excitatory amino acid receptors, thereby blocking the actions of agonists. 
• Expectorants Agents that increase mucous excretion. Mucolytic agents, that is drugs that liquefy mucous secretions, are also included here. 
• Explosive Agents Substances that are energetically unstable and can produce a sudden expansion of the material, called an explosion, which is accompanied by heat, pressure and noise. Other things which have been described as explosive that are not included here are explosive action of laser heating, human performance, sudden epidemiological outbreaks, or fast cell growth. 
• Factor Xa Inhibitors Endogenous factors and drugs that inhibit or block the activity of FACTOR XA. 
• Fat Emulsions, Intravenous Emulsions of fats or lipids used primarily in parenteral feeding. 
• Fat Substitutes Compounds used in food or in food preparation to replace dietary fats. They may be carbohydrate-, protein-, or fat-based. Fat substitutes are usually lower in calories but provide the same texture as fats. 
• Fatty Acid Synthesis Inhibitors Compounds that interfere with FATTY ACID SYNTHASE resulting in a reduction of FATTY ACIDS. This is a target mechanism in humans of some ANTINEOPLASTIC AGENTS and ANTI-OBESITY AGENTS and of some ANTI-INFECTIVE AGENTS which interfere with CELL WALL and CELL MEMBRANE formation. 
• Fertility Agents, Female Compounds which increase the capacity to conceive in females. 
• Fertility Agents, Male Compounds which increase the capacity of the male to induce conception. 
• Fertilizers Substances or mixtures that are added to the soil to supply nutrients or to make available nutrients already present in the soil, in order to increase plant growth and productivity. 
• Fibrinolytic Agents Fibrinolysin or agents that convert plasminogen to FIBRINOLYSIN. 
• Filaricides Pharmacological agents destructive to nematodes in the superfamily Filarioidea. 
• Fixatives Agents employed in the preparation of histologic or pathologic specimens for the purpose of maintaining the existing form and structure of all of the constituent elements. Great numbers of different agents are used; some are also decalcifying and hardening agents. They must quickly kill and coagulate living tissue. 
• Flame Retardants Materials applied to fabrics, bedding, furniture, plastics, etc. to retard their burning; many may leach out and cause allergies or other harm. 
• Flavoring Agents Substances added to foods and medicine to improve the quality of taste. 
• Fluorescent Dyes Agents that emit light after excitation by light. The wave length of the emitted light is usually longer than that of the incident light. Fluorochromes are substances that cause fluorescence in other substances, i.e., dyes used to mark or label other compounds with fluorescent tags. 
• Folic Acid Antagonists Inhibitors of the enzyme, dihydrofolate reductase , which converts dihydrofolate to tetrahydrofolate . They are frequently used in cancer chemotherapy.  
• Food Additives Substances which are of little or no nutritive value, but are used in the processing or storage of foods or animal feed, especially in the developed countries; includes ANTIOXIDANTS; FOOD PRESERVATIVES; FOOD COLORING AGENTS; FLAVORING AGENTS; ANTI-INFECTIVE AGENTS ; VEHICLES; EXCIPIENTS and other similarly used substances. Many of the same substances are PHARMACEUTIC AIDS when added to pharmaceuticals rather than to foods. 
• Food Coloring Agents Natural or synthetic dyes used as coloring agents in processed foods. 
• Food Preservatives Substances capable of inhibiting, retarding or arresting the process of fermentation, acidification or other deterioration of foods. 
• Free Radical Scavengers Substances that influence the course of a chemical reaction by ready combination with free radicals. Among other effects, this combining activity protects pancreatic islets against damage by cytokines and prevents myocardial and pulmonary perfusion injuries. 
• GABA Agents Substances used for their pharmacological actions on GABAergic systems. GABAergic agents include agonists, antagonists, degradation or uptake inhibitors, depleters, precursors, and modulators of receptor function. 
• GABA Agonists Endogenous compounds and drugs that bind to and activate GAMMA-AMINOBUTYRIC ACID receptors . 
• GABA Antagonists Drugs that bind to but do not activate GABA RECEPTORS, thereby blocking the actions of endogenous GAMMA-AMINOBUTYRIC ACID and GABA RECEPTOR AGONISTS. 
• GABA Modulators Substances that do not act as agonists or antagonists but do affect the GAMMA-AMINOBUTYRIC ACID receptor-ionophore complex. GABA-A receptors appear to have at least three allosteric sites at which modulators act: a site at which BENZODIAZEPINES act by increasing the opening frequency of GAMMA-AMINOBUTYRIC ACID-activated chloride channels; a site at which BARBITURATES act to prolong the duration of channel opening; and a site at which some steroids may act. GENERAL ANESTHETICS probably act at least partly by potentiating GABAergic responses, but they are not included here. 
• GABA-A Receptor Agonists Endogenous compounds and drugs that bind to and activate GABA-A RECEPTORS. 
• GABA-A Receptor Antagonists Drugs that bind to but do not activate GABA-A RECEPTORS thereby blocking the actions of endogenous or exogenous GABA-A RECEPTOR AGONISTS. 
• GABA-B Receptor Agonists Endogenous compounds and drugs that bind to and activate GABA-B RECEPTORS. 
• GABA-B Receptor Antagonists Drugs that bind to but do not activate GABA-B RECEPTORS thereby blocking the actions of endogenous or exogenous GABA-B RECEPTOR AGONISTS. 
• GTP Phosphohydrolase Activators Agents and factors that activate GTP phosphohydrolase activity. 
• Ganglionic Blockers Agents having as their major action the interruption of neural transmission at nicotinic receptors on postganglionic autonomic neurons. Because their actions are so broad, including blocking of sympathetic and parasympathetic systems, their therapeutic use has been largely supplanted by more specific drugs. They may still be used in the control of blood pressure in patients with acute dissecting aortic aneurysm and for the induction of hypotension in surgery. 
• Ganglionic Stimulants Agents that mimic neural transmission by stimulation of the nicotinic receptors on postganglionic autonomic neurons. Drugs that indirectly augment ganglionic transmission by increasing the release or slowing the breakdown of acetylcholine or by non-nicotinic effects on postganglionic neurons are not included here nor are the nonspecific cholinergic agonists. 
• Gasotransmitters Endogenously produced lipid-soluble gaseous molecules which function as neurotransmitters and signal mediators targeting ION CHANNELS and transporters. 
• Gastrointestinal Agents Drugs used for their effects on the gastrointestinal system, as to control gastric acidity, regulate gastrointestinal motility and water flow, and improve digestion. 
• Glucocorticoids A group of CORTICOSTEROIDS that affect carbohydrate metabolism , inhibit ADRENOCORTICOTROPIC HORMONE secretion, and possess pronounced anti-inflammatory activity. They also play a role in fat and protein metabolism, maintenance of arterial blood pressure, alteration of the connective tissue response to injury, reduction in the number of circulating lymphocytes, and functioning of the central nervous system. 
• Glycine Agents Substances used for their pharmacological actions on glycinergic systems. Glycinergic agents include agonists, antagonists, degradation or uptake inhibitors, depleters, precursors, and modulators of receptor function. 
• Glycoside Hydrolase Inhibitors Compounds that inhibit or block the activity of GLYCOSIDE HYDROLASES such as ALPHA-AMYLASES and APHA-GLUCOSIDASES. 
• Gout Suppressants Agents that increase uric acid excretion by the kidney , decrease uric acid production , or alleviate the pain and inflammation of acute attacks of gout. 
• Growth Inhibitors Endogenous or exogenous substances which inhibit the normal growth of human and animal cells or micro-organisms, as distinguished from those affecting plant growth . 
• HIV Integrase Inhibitors Inhibitors of HIV INTEGRASE, an enzyme required for integration of viral DNA into cellular DNA. 
• HIV Protease Inhibitors Inhibitors of HIV PROTEASE, an enzyme required for production of proteins needed for viral assembly. 
• Hallucinogens Drugs capable of inducing illusions, hallucinations, delusions, paranoid ideations, and other alterations of mood and thinking. Despite the name, the feature that distinguishes these agents from other classes of drugs is their capacity to induce states of altered perception, thought, and feeling that are not experienced otherwise. 
• Hazardous Substances Elements, compounds, mixtures, or solutions that are considered severely harmful to human health and the environment. They include substances that are toxic, corrosive, flammable, or explosive. 
• Hemagglutinins Agents that cause agglutination of red blood cells. They include antibodies, blood group antigens, lectins, autoimmune factors, bacterial, viral, or parasitic blood agglutinins, etc. 
• Hematinics Agents which improve the quality of the blood, increasing the hemoglobin level and the number of erythrocytes. They are used in the treatment of anemias. 
• Hematologic Agents Drugs that act on blood and blood-forming organs and those that affect the hemostatic system. 
• Hemolytic Agents Substances that are toxic to blood in general, including the clotting mechanism; hematotoxins may refer to the hematopoietic system. 
• Hemostatics Agents acting to arrest the flow of blood. Absorbable hemostatics arrest bleeding either by the formation of an artificial clot or by providing a mechanical matrix that facilitates clotting when applied directly to the bleeding surface. These agents function more at the capillary level and are not effective at stemming arterial or venous bleeding under any significant intravascular pressure. 
• Heparin Antagonists Coagulant substances inhibiting the anticoagulant action of heparin. 
• Herbicides Pesticides used to destroy unwanted vegetation, especially various types of weeds, grasses , and woody plants. Some plants develop HERBICIDE RESISTANCE. 
• Histamine Agents Drugs used for their actions on histaminergic systems. Included are drugs that act at histamine receptors, affect the life cycle of histamine, or affect the state of histaminergic cells. 
• Histamine Agonists Drugs that bind to and activate histamine receptors. Although they have been suggested for a variety of clinical applications histamine agonists have so far been more widely used in research than therapeutically. 
• Histamine Antagonists Drugs that bind to but do not activate histamine receptors, thereby blocking the actions of histamine or histamine agonists. Classical antihistaminics block the histamine H1 receptors only. 
• Histamine H1 Antagonists, Non-Sedating A class of non-sedating drugs that bind to but do not activate histamine receptors , thereby blocking the actions of histamine or histamine agonists. These antihistamines represent a heterogenous group of compounds with differing chemical structures, adverse effects, distribution, and metabolism. Compared to the early antihistamines, these non-sedating antihistamines have greater receptor specificity, lower penetration of BLOOD-BRAIN BARRIER, and are less likely to cause drowsiness or psychomotor impairment. 
• Histamine H1 Antagonists Drugs that selectively bind to but do not activate histamine H1 receptors, thereby blocking the actions of endogenous histamine. Included here are the classical antihistaminics that antagonize or prevent the action of histamine mainly in immediate hypersensitivity. They act in the bronchi, capillaries, and some other smooth muscles, and are used to prevent or allay motion sickness, seasonal rhinitis, and allergic dermatitis and to induce somnolence. The effects of blocking central nervous system H1 receptors are not as well understood. 
• Histamine H2 Antagonists Drugs that selectively bind to but do not activate histamine H2 receptors, thereby blocking the actions of histamine. Their clinically most important action is the inhibition of acid secretion in the treatment of gastrointestinal ulcers. Smooth muscle may also be affected. Some drugs in this class have strong effects in the central nervous system, but these actions are not well understood. 
• Histamine H3 Antagonists Drugs that selectively bind to but do not activate HISTAMINE H3 RECEPTORS. They have been used to correct SLEEP WAKE DISORDERS and MEMORY DISORDERS. 
• Histone Deacetylase Inhibitors Compounds that inhibit HISTONE DEACETYLASES. This class of drugs may influence gene expression by increasing the level of acetylated HISTONES in specific CHROMATIN domains. 
• Hormone Antagonists Chemical substances which inhibit the function of the endocrine glands, the biosynthesis of their secreted hormones, or the action of hormones upon their specific sites. 
• Hormones Chemical substances having a specific regulatory effect on the activity of a certain organ or organs. The term was originally applied to substances secreted by various ENDOCRINE GLANDS and transported in the bloodstream to the target organs. It is sometimes extended to include those substances that are not produced by the endocrine glands but that have similar effects. 
• Hydroxymethylglutaryl-CoA Reductase Inhibitors Compounds that inhibit HMG-CoA reductases. They have been shown to directly lower cholesterol synthesis. 
• Hypnotics and Sedatives Drugs used to induce drowsiness or sleep or to reduce psychological excitement or anxiety. 
• Immunologic Factors Biologically active substances whose activities affect or play a role in the functioning of the immune system. 
• Immunosuppressive Agents Agents that suppress immune function by one of several mechanisms of action. Classical cytotoxic immunosuppressants act by inhibiting DNA synthesis. Others may act through activation of T-CELLS or by inhibiting the activation of HELPER CELLS. While immunosuppression has been brought about in the past primarily to prevent rejection of transplanted organs, new applications involving mediation of the effects of INTERLEUKINS and other CYTOKINES are emerging. 
• Incretins Peptides which stimulate INSULIN release from the PANCREATIC BETA CELLS following oral nutrient ingestion, or postprandially. 
• Indicators and Reagents Substances used for the detection, identification, analysis, etc. of chemical, biological, or pathologic processes or conditions. Indicators are substances that change in physical appearance, e.g., color, at or approaching the endpoint of a chemical titration, e.g., on the passage between acidity and alkalinity. Reagents are substances used for the detection or determination of another substance by chemical or microscopical means, especially analysis. Types of reagents are precipitants, solvents, oxidizers, reducers, fluxes, and colorimetric reagents.  
• Insect Repellents Substances causing insects to turn away from them or reject them as food. 
• Insecticides Pesticides designed to control insects that are harmful to man. The insects may be directly harmful, as those acting as disease vectors, or indirectly harmful, as destroyers of crops, food products, or textile fabrics. 
• Insulin Antagonists Compounds which inhibit or antagonize the biosynthesis or action of insulin. 
• Intercalating Agents Agents that are capable of inserting themselves between the successive bases in DNA, thus kinking, uncoiling or otherwise deforming it and therefore preventing its proper functioning. They are used in the study of DNA. 
• Interferon Inducers Agents that promote the production and release of interferons. They include mitogens, lipopolysaccharides, and the synthetic polymers Poly A-U and Poly I-C. Viruses, bacteria, and protozoa have been also known to induce interferons. 
• Ionophores Chemical agents that increase the permeability of biological or artificial lipid membranes to specific ions. Most ionophores are relatively small organic molecules that act as mobile carriers within membranes or coalesce to form ion permeable channels across membranes. Many are antibiotics, and many act as uncoupling agents by short-circuiting the proton gradient across mitochondrial membranes. 
• Iron Chelating Agents Organic chemicals that form two or more coordination links with an iron ion. Once coordination has occurred, the complex formed is called a chelate. The iron-binding porphyrin group of hemoglobin is an example of a metal chelate found in biological systems. 
• Irritants Drugs that act locally on cutaneous or mucosal surfaces to produce inflammation; those that cause redness due to hyperemia are rubefacients; those that raise blisters are vesicants and those that penetrate sebaceous glands and cause abscesses are pustulants; tear gases and mustard gases are also irritants. 
• Keratolytic Agents Agents that soften, separate, and cause desquamation of the cornified epithelium or horny layer of skin. They are used to expose mycelia of infecting fungi or to treat corns, warts, and certain other skin diseases. 
• Laxatives Agents that produce a soft formed stool, and relax and loosen the bowels, typically used over a protracted period, to relieve CONSTIPATION. 
• Leprostatic Agents Substances that suppress Mycobacterium leprae, ameliorate the clinical manifestations of leprosy, and/or reduce the incidence and severity of leprous reactions. 
• Leukotriene Antagonists A class of drugs designed to prevent leukotriene synthesis or activity by blocking binding at the receptor level. 
• Lipoprotein Lipase Activators Compounds that increase the enzymatic activity of LIPOPROTEIN LIPASE. Lipoprotein lipase activators have a potential role in the treatment of OBESITY by increasing LIPID METABOLISM. Note that substances that increase the synthesis of lipoprotein lipase are not included here. 
• Lipotropic Agents Endogenous factors or drugs that increase the transport and metabolism of LIPIDS including the synthesis of LIPOPROTEINS by the LIVER and their uptake by extrahepatic tissues. 
• Lipoxygenase Inhibitors Compounds that bind to and inhibit that enzymatic activity of LIPOXYGENASES. Included under this category are inhibitors that are specific for lipoxygenase subtypes and act to reduce the production of LEUKOTRIENES. 
• Matrix Metalloproteinase Inhibitors Compounds that inhibit the enzyme activity or activation of MATRIX METALLOPROTEINASES. 
• Membrane Transport Modulators Agents that affect ION PUMPS; ION CHANNELS; ABC TRANSPORTERS; and other MEMBRANE TRANSPORT PROTEINS. 
• Menstruation-Inducing Agents Chemical compounds that induce menstruation either through direct action on the reproductive organs or through indirect action by relieving another condition of which amenorrhea is a secondary result.  
• Micronutrients Essential dietary elements or organic compounds that are required in only small quantities for normal physiologic processes to occur. 
• Mineralocorticoid Receptor Antagonists Drugs that bind to and block the activation of MINERALOCORTICOID RECEPTORS by MINERALOCORTICOIDS such as ALDOSTERONE. 
• Mineralocorticoids A group of CORTICOSTEROIDS primarily associated with water and electrolyte balance. This is accomplished through the effect on ION TRANSPORT in renal tubules, resulting in retention of sodium and loss of potassium. Mineralocorticoid secretion is itself regulated by PLASMA VOLUME, serum potassium, and ANGIOTENSIN II. 
• Miotics Agents causing contraction of the pupil of the eye. Some sources use the term miotics only for the parasympathomimetics but any drug used to induce miosis is included here. 
• Mitogens Substances that stimulate mitosis and lymphocyte transformation. They include not only substances associated with LECTINS, but also substances from streptococci and from strains of alpha-toxin-producing staphylococci.  
• Monoamine Oxidase Inhibitors A chemically heterogeneous group of drugs that have in common the ability to block oxidative deamination of naturally occurring monoamines.  
• Mouthwashes Solutions for rinsing the mouth, possessing cleansing, germicidal, or palliative properties.  
• Muscarinic Agonists Drugs that bind to and activate muscarinic cholinergic receptors . Muscarinic agonists are most commonly used when it is desirable to increase smooth muscle tone, especially in the GI tract, urinary bladder and the eye. They may also be used to reduce heart rate. 
• Muscarinic Antagonists Drugs that bind to but do not activate MUSCARINIC RECEPTORS, thereby blocking the actions of endogenous ACETYLCHOLINE or exogenous agonists. Muscarinic antagonists have widespread effects including actions on the iris and ciliary muscle of the eye, the heart and blood vessels, secretions of the respiratory tract, GI system, and salivary glands, GI motility, urinary bladder tone, and the central nervous system. 
• Muscle Relaxants, Central A heterogeneous group of drugs used to produce muscle relaxation, excepting the neuromuscular blocking agents. They have their primary clinical and therapeutic uses in the treatment of muscle spasm and immobility associated with strains, sprains, and injuries of the back and, to a lesser degree, injuries to the neck. They have been used also for the treatment of a variety of clinical conditions that have in common only the presence of skeletal muscle hyperactivity, for example, the muscle spasms that can occur in MULTIPLE SCLEROSIS.  
• Mutagens Chemical agents that increase the rate of genetic mutation by interfering with the function of nucleic acids. A clastogen is a specific mutagen that causes breaks in chromosomes. 
• Mydriatics Agents that dilate the pupil. They may be either sympathomimetics or parasympatholytics. 
• Narcotic Antagonists Agents inhibiting the effect of narcotics on the central nervous system. 
• Narcotics Agents that induce NARCOSIS. Narcotics include agents that cause somnolence or induced sleep ; natural or synthetic derivatives of OPIUM or MORPHINE or any substance that has such effects. They are potent inducers of ANALGESIA and OPIOID-RELATED DISORDERS. 
• Nasal Decongestants Drugs designed to treat inflammation of the nasal passages, generally the result of an infection or an allergy related condition, e.g., hay fever. The inflammation involves swelling of the mucous membrane that lines the nasal passages and results in inordinate mucus production. The primary class of nasal decongestants are vasoconstrictor agents.  
• Natriuretic Agents Endogenous or exogenous chemicals that regulate the WATER-ELECTROLYTE BALANCE in the body. They consist of peptides and non-peptide compounds. 
• Neurokinin-1 Receptor Antagonists Compounds that inhibit or block the activity of NEUROKININ-1 RECEPTORS. 
• Neuromuscular Agents Drugs used for their actions on skeletal muscle. Included are agents that act directly on skeletal muscle, those that alter neuromuscular transmission , and drugs that act centrally as skeletal muscle relaxants . Drugs used in the treatment of movement disorders are ANTI-DYSKINESIA AGENTS. 
• Neuromuscular Blocking Agents Drugs that interrupt transmission of nerve impulses at the skeletal neuromuscular junction. They can be of two types, competitive, stabilizing blockers or noncompetitive, depolarizing agents . Both prevent acetylcholine from triggering the muscle contraction and they are used as anesthesia adjuvants, as relaxants during electroshock, in convulsive states, etc. 
• Neuromuscular Depolarizing Agents Drugs that interrupt transmission at the skeletal neuromuscular junction by causing sustained depolarization of the motor end plate. These agents are primarily used as adjuvants in surgical anesthesia to cause skeletal muscle relaxation. 
• Neuromuscular Nondepolarizing Agents Drugs that interrupt transmission at the skeletal neuromuscular junction without causing depolarization of the motor end plate. They prevent acetylcholine from triggering muscle contraction and are used as muscle relaxants during electroshock treatments, in convulsive states, and as anesthesia adjuvants. 
• Neuroprotective Agents Drugs intended to prevent damage to the brain or spinal cord from ischemia, stroke, convulsions, or trauma. Some must be administered before the event, but others may be effective for some time after. They act by a variety of mechanisms, but often directly or indirectly minimize the damage produced by endogenous excitatory amino acids. 
• Neurotoxins Toxic substances from microorganisms, plants or animals that interfere with the functions of the nervous system. Most venoms contain neurotoxic substances. Myotoxins are included in this concept. 
• Neurotransmitter Agents Substances used for their pharmacological actions on any aspect of neurotransmitter systems. Neurotransmitter agents include agonists, antagonists, degradation inhibitors, uptake inhibitors, depleters, precursors, and modulators of receptor function. 
• Neurotransmitter Uptake Inhibitors Drugs that inhibit the transport of neurotransmitters into axon terminals or into storage vesicles within terminals. For many transmitters, uptake determines the time course of transmitter action so inhibiting uptake prolongs the activity of the transmitter. Blocking uptake may also deplete available transmitter stores. Many clinically important drugs are uptake inhibitors although the indirect reactions of the brain rather than the acute block of uptake itself is often responsible for the therapeutic effects. 
• Nicotinic Agonists Drugs that bind to and activate nicotinic cholinergic receptors . Nicotinic agonists act at postganglionic nicotinic receptors, at neuroeffector junctions in the peripheral nervous system, and at nicotinic receptors in the central nervous system. Agents that function as neuromuscular depolarizing blocking agents are included here because they activate nicotinic receptors, although they are used clinically to block nicotinic transmission. 
• Nicotinic Antagonists Drugs that bind to nicotinic cholinergic receptors and block the actions of acetylcholine or cholinergic agonists. Nicotinic antagonists block synaptic transmission at autonomic ganglia, the skeletal neuromuscular junction, and at central nervous system nicotinic synapses. 
• Nitric Oxide Donors A diverse group of agents, with unique chemical structures and biochemical requirements, which generate NITRIC OXIDE. These compounds have been used in the treatment of cardiovascular diseases and the management of acute myocardial infarction, acute and chronic congestive heart failure, and surgical control of blood pressure.  
• Nootropic Agents Drugs used to specifically facilitate learning or memory, particularly to prevent the cognitive deficits associated with dementias. These drugs act by a variety of mechanisms. While no potent nootropic drugs have yet been accepted for general use, several are being actively investigated. 
• Ointment Bases Various mixtures of fats, waxes, animal and plant oils and solid and liquid hydrocarbons; vehicles for medicinal substances intended for external application; there are four classes: hydrocarbon base, absorption base, water-removable base and water-soluble base; several are also emollients. 
• Oligonucleotides, Antisense Short fragments of DNA or RNA that are used to alter the function of target RNAs or DNAs to which they hybridize. 
• Ophthalmic Solutions Sterile solutions that are intended for instillation into the eye. It does not include solutions for cleaning eyeglasses or CONTACT LENS SOLUTIONS. 
• Ornithine Decarboxylase Inhibitors Substances and drugs that inhibit or block the activity of ORNITHINE DECARBOXYLASE. 
• Oxidants, Photochemical Compounds that accept electrons in an oxidation-reduction reaction. The reaction is induced by or accelerated by exposure to electromagnetic radiation in the spectrum of visible or ultraviolet light. 
• Oxidants Electron-accepting molecules in chemical reactions in which electrons are transferred from one molecule to another . 
• Parasympatholytics Agents that inhibit the actions of the parasympathetic nervous system. The major group of drugs used therapeutically for this purpose is the MUSCARINIC ANTAGONISTS. 
• Parasympathomimetics Drugs that mimic the effects of parasympathetic nervous system activity. Included here are drugs that directly stimulate muscarinic receptors and drugs that potentiate cholinergic activity, usually by slowing the breakdown of acetylcholine . Drugs that stimulate both sympathetic and parasympathetic postganglionic neurons are not included here. 
• Parenteral Nutrition Solutions Specialized solutions for PARENTERAL NUTRITION. They may contain a variety of MICRONUTRIENTS; VITAMINS; AMINO ACIDS; CARBOHYDRATES; LIPIDS; and SALTS. 
• Perfume A substance, extract, or preparation for diffusing or imparting an agreeable or attractive smell, especially a fluid containing fragrant natural oils extracted from flowers, woods, etc., or similar synthetic oils.  
• Peroxisome Proliferators A class of nongenotoxic CARCINOGENS that induce the production of hepatic PEROXISOMES and induce hepatic neoplasms after long-term administration. 
• Pesticide Synergists Chemicals that, while not possessing inherent pesticidal activity, nonetheless promote or enhance the effectiveness of other pesticides when combined. 
• Pesticides Chemicals used to destroy pests of any sort. The concept includes fungicides ; INSECTICIDES; RODENTICIDES; etc. 
• Pharmaceutic Aids Substances which are of little or no therapeutic value, but are necessary in the manufacture, compounding, storage, etc., of pharmaceutical preparations or drug dosage forms. They include SOLVENTS, diluting agents, and suspending agents, and emulsifying agents. Also, ANTIOXIDANTS; PRESERVATIVES, PHARMACEUTICAL; COLORING AGENTS; FLAVORING AGENTS; VEHICLES; EXCIPIENTS; OINTMENT BASES. 
• Pharmaceutical Vehicles A carrier or inert medium used as a solvent in which the medicinally active agent is formulated and or administered.  
• Phosphodiesterase 3 Inhibitors Compounds that specifically inhibit PHOSPHODIESTERASE 3. 
• Phosphodiesterase 4 Inhibitors Compounds that specifically inhibit PHOSPHODIESTERASE 4. 
• Phosphodiesterase 5 Inhibitors Compounds that specifically inhibit PHOSPHODIESTERASE 5. 
• Phosphodiesterase Inhibitors Compounds which inhibit or antagonize the biosynthesis or actions of phosphodiesterases. 
• Photoaffinity Labels Biologically active molecules which are covalently bound to the enzymes or binding proteins normally acting on them. Binding occurs due to activation of the label by ultraviolet light. These labels are used primarily to identify binding sites on proteins. 
• Photosensitizing Agents Drugs that are pharmacologically inactive but when exposed to ultraviolet radiation or sunlight are converted to their active metabolite to produce a beneficial reaction affecting the diseased tissue. These compounds can be administered topically or systemically and have been used therapeutically to treat psoriasis and various types of neoplasms. 
• Phytoestrogens PLANT EXTRACTS and compounds, primarily ISOFLAVONES, that mimic or modulate endogenous estrogens, usually by binding to ESTROGEN RECEPTORS. 
• Plant Growth Regulators Any of the hormones produced naturally in plants and active in controlling growth and other functions. There are three primary classes: auxins, cytokinins, and gibberellins. 
• Plasma Substitutes Any liquid used to replace blood plasma, usually a saline solution, often with serum albumins, dextrans or other preparations. These substances do not enhance the oxygen- carrying capacity of blood, but merely replace the volume. They are also used to treat dehydration. 
• Plasticizers Materials incorporated mechanically in plastics to increase flexibility, workability or distensibility; due to the non-chemical inclusion, plasticizers leach out from the plastic and are found in body fluids and the general environment. 
• Platelet Aggregation Inhibitors Drugs or agents which antagonize or impair any mechanism leading to blood platelet aggregation, whether during the phases of activation and shape change or following the dense-granule release reaction and stimulation of the prostaglandin-thromboxane system. 
• Poisons Substances which, when ingested, inhaled, or absorbed, or when applied to, injected into, or developed within the body in relatively small amounts may, by their chemical action, cause damage to structure or disturbance of function.  
• Poly Polymerase Inhibitors Chemicals and drugs that inhibit the action of POLYPOLYMERASES. 
• Potassium Channel Blockers A class of drugs that act by inhibition of potassium efflux through cell membranes. Blockade of potassium channels prolongs the duration of ACTION POTENTIALS. They are used as ANTI-ARRHYTHMIA AGENTS and VASODILATOR AGENTS. 
• Preservatives, Pharmaceutical Substances added to pharmaceutical preparations to protect them from chemical change or microbial action. They include ANTI-BACTERIAL AGENTS and antioxidants. 
• Progestins Compounds that interact with PROGESTERONE RECEPTORS in target tissues to bring about the effects similar to those of PROGESTERONE. Primary actions of progestins, including natural and synthetic steroids, are on the UTERUS and the MAMMARY GLAND in preparation for and in maintenance of PREGNANCY. 
• Protease Inhibitors Compounds which inhibit or antagonize biosynthesis or actions of proteases . 
• Protective Agents Synthetic or natural substances which are given to prevent a disease or disorder or are used in the process of treating a disease or injury due to a poisonous agent. 
• Protein Synthesis Inhibitors Compounds which inhibit the synthesis of proteins. They are usually ANTI-BACTERIAL AGENTS or toxins. Mechanism of the action of inhibition includes the interruption of peptide-chain elongation, the blocking the A site of ribosomes, the misreading of the genetic code or the prevention of the attachment of oligosaccharide side chains to glycoproteins. 
• Proton Ionophores Chemical agents that increase the permeability of CELL MEMBRANES to PROTONS. 
• Proton Pump Inhibitors Compounds that inhibit H-K-EXCHANGING ATPASE. They are used as ANTI-ULCER AGENTS and sometimes in place of HISTAMINE H2 ANTAGONISTS for GASTROESOPHAGEAL REFLUX. 
• Psychotropic Drugs A loosely defined grouping of drugs that have effects on psychological function. Here the psychotropic agents include the antidepressive agents, hallucinogens, and tranquilizing agents . 
• Pulmonary Surfactants Substances and drugs that lower the SURFACE TENSION of the mucoid layer lining the PULMONARY ALVEOLI. 
• Purinergic P1 Receptor Agonists Compounds that bind to and stimulate PURINERGIC P1 RECEPTORS. 
• Purinergic P1 Receptor Antagonists Compounds that bind to and block the stimulation of PURINERGIC P1 RECEPTORS. 
• Purinergic P2 Receptor Antagonists Compounds that bind to and block the stimulation of PURINERGIC P2 RECEPTORS. 
• Purinergic P2Y Receptor Antagonists Compounds that bind to and block the stimulation of PURINERGIC P2Y RECEPTORS. Included under this heading are antagonists for specific P2Y receptor subtypes. 
• Radiation-Protective Agents Drugs used to protect against ionizing radiation. They are usually of interest for use in radiation therapy but have been considered for other, e.g. military, purposes. 
• Radiation-Sensitizing Agents Drugs used to potentiate the effectiveness of radiation therapy in destroying unwanted cells. 
• Radiopharmaceuticals Compounds that are used in medicine as sources of radiation for radiotherapy and for diagnostic purposes. They have numerous uses in research and industry.  
• Reducing Agents Materials that add an electron to an element or compound, that is, decrease the positiveness of its valence.  
• Reproductive Control Agents Substances used either in the prevention or facilitation of pregnancy. 
• Reverse Transcriptase Inhibitors Inhibitors of reverse transcriptase , an enzyme that synthesizes DNA on an RNA template. 
• Riot Control Agents, Chemical Chemical substances which are employed during a riot in order to control or disperse the rioting parties. 
• Rodenticides Substances used to destroy or inhibit the action of rats, mice, or other rodents. 
• Sclerosing Solutions Chemical agents injected into blood vessels and lymphatic sinuses to shrink or cause localized THROMBOSIS; FIBROSIS, and obliteration of the vessels. This treatment is applied in a number of conditions such as VARICOSE VEINS; HEMORRHOIDS; GASTRIC VARICES; ESOPHAGEAL VARICES; PEPTIC ULCER HEMORRHAGE. 
• Selective Angiotensin II Receptor Antagonists See Angiotensin II Type 1 Receptor Blockers
• Selective Estrogen Receptor Modulators A structurally diverse group of compounds distinguished from ESTROGENS by their ability to bind and activate ESTROGEN RECEPTORS but act as either an agonist or antagonist depending on the tissue type and hormonal milieu. They are classified as either first generation because they demonstrate estrogen agonist properties in the ENDOMETRIUM or second generation based on their patterns of tissue specificity.  
• Sensory System Agents Drugs that act on neuronal sensory receptors resulting in an increase, decrease, or modification of afferent nerve activity.  
• Sequestering Agents Compounds that bind to and reduce the biological availability of a chemical or pharmaceutical agent. 
• Serine Proteinase Inhibitors Exogenous or endogenous compounds which inhibit SERINE ENDOPEPTIDASES. 
• Serotonin 5-HT1 Receptor Agonists Endogenous compounds and drugs that specifically stimulate SEROTONIN 5-HT1 RECEPTORS. Included under this heading are agonists for one or more of the specific 5-HT1 receptor subtypes. 
• Serotonin 5-HT1 Receptor Antagonists Drugs that bind to but do not activate SEROTONIN 5-HT1 RECEPTORS, thereby blocking the actions of SEROTONIN 5-HT1 RECEPTOR AGONISTS. Included under this heading are antagonists for one or more of the specific 5-HT1 receptor subtypes. 
• Serotonin 5-HT2 Receptor Antagonists Drugs that bind to but do not activate SEROTONIN 5-HT2 RECEPTORS, thereby blocking the actions of SEROTONIN or SEROTONIN 5-HT2 RECEPTOR AGONISTS. Included under this heading are antagonists for one or more specific 5-HT2 receptor subtypes. 
• Serotonin Agents Drugs used for their effects on serotonergic systems. Among these are drugs that affect serotonin receptors, the life cycle of serotonin, and the survival of serotonergic neurons. 
• Serotonin Antagonists Drugs that bind to but do not activate serotonin receptors, thereby blocking the actions of serotonin or SEROTONIN RECEPTOR AGONISTS. 
• Serotonin Receptor Agonists Endogenous compounds and drugs that bind to and activate SEROTONIN RECEPTORS. Many serotonin receptor agonists are used as ANTIDEPRESSANTS; ANXIOLYTICS; and in the treatment of MIGRAINE DISORDERS. 
• Serotonin Uptake Inhibitors Compounds that specifically inhibit the reuptake of serotonin in the brain. 
• Serotonin and Noradrenaline Reuptake Inhibitors Drugs that selectively block or suppress the plasma membrane transport of SEROTONIN and NORADRENALINE into axon terminals and are used as ANTIDEPRESSIVE AGENTS. 
• Siderophores Low-molecular-weight compounds produced by microorganisms that aid in the transport and sequestration of ferric iron.  
• Sleep Aids, Pharmaceutical Drugs used to induce SLEEP, prevent SLEEPLESSNESS, or treat SLEEP INITIATION AND MAINTENANCE DISORDERS. 
• Sodium Channel Blockers A class of drugs that act by inhibition of sodium influx through cell membranes. Blockade of sodium channels slows the rate and amplitude of initial rapid depolarization, reduces cell excitability, and reduces conduction velocity. 
• Sodium Chloride Symporter Inhibitors Agents that inhibit SODIUM CHLORIDE SYMPORTERS. They act as DIURETICS. Excess use is associated with HYPOKALEMIA. 
• Sodium Ionophores Chemical agents that increase the permeability of CELL MEMBRANES to SODIUM ions. 
• Sodium Potassium Chloride Symporter Inhibitors Agents that inhibit SODIUM-POTASSIUM-CHLORIDE SYMPORTERS which are concentrated in the thick ascending limb at the junction of the LOOP OF HENLE and KIDNEY TUBULES, DISTAL. They act as DIURETICS. Excess use is associated with HYPOKALEMIA and HYPERGLYCEMIA. 
• Soil Pollutants Substances which pollute the soil. Use for soil pollutants in general or for which there is no specific heading. 
• Solvents Liquids that dissolve other substances , generally solids, without any change in chemical composition, as, water containing sugar.  
• Spermatocidal Agents Chemical substances that are destructive to spermatozoa used as topically administered vaginal contraceptives. 
• Steroid Synthesis Inhibitors Compounds that bind to and inhibit enzymes involved in the synthesis of STEROIDS. 
• Sulfhydryl Reagents Chemical agents that react with SH groups. This is a chemically diverse group that is used for a variety of purposes. Among these are enzyme inhibition, enzyme reactivation or protection, and labelling. 
• Sunscreening Agents Chemical or physical agents that protect the skin from sunburn and erythema by absorbing or blocking ultraviolet radiation. 
• Surface-Active Agents Agents that modify interfacial tension of water; usually substances that have one lipophilic and one hydrophilic group in the molecule; includes soaps, detergents, emulsifiers, dispersing and wetting agents, and several groups of antiseptics. 
• Sweetening Agents Substances that sweeten food, beverages, medications, etc., such as sugar, saccharine or other low-calorie synthetic products.  
• Sympatholytics Drugs that inhibit the actions of the sympathetic nervous system by any mechanism. The most common of these are the ADRENERGIC ANTAGONISTS and drugs that deplete norepinephrine or reduce the release of transmitters from adrenergic postganglionic terminals . Drugs that act in the central nervous system to reduce sympathetic activity are included here. 
• Sympathomimetics Drugs that mimic the effects of stimulating postganglionic adrenergic sympathetic nerves. Included here are drugs that directly stimulate adrenergic receptors and drugs that act indirectly by provoking the release of adrenergic transmitters. 
• Tear Gases Gases that irritate the eyes, throat, or skin. Severe lacrimation develops upon irritation of the eyes. 
• Teratogens An agent that causes the production of physical defects in the developing embryo. 
• Tissue Adhesives Substances used to cause adherence of tissue to tissue or tissue to non-tissue surfaces, as for prostheses. 
• Tocolytic Agents Drugs that prevent preterm labor and immature birth by suppressing uterine contractions . Agents used to delay premature uterine activity include magnesium sulfate, beta-mimetics, oxytocin antagonists, calcium channel inhibitors, and adrenergic beta-receptor agonists. The use of intravenous alcohol as a tocolytic is now obsolete. 
• Tooth Bleaching Agents Chemicals that are used to oxidize pigments in TEETH and thus effect whitening. 
• Topoisomerase I Inhibitors Compounds that inhibit the activity of DNA TOPOISOMERASE I. 
• Topoisomerase II Inhibitors Compounds that inhibit the activity of DNA TOPOISOMERASE II. Included in this category are a variety of ANTINEOPLASTIC AGENTS which target the eukaryotic form of topoisomerase II and ANTIBACTERIAL AGENTS which target the prokaryotic form of topoisomerase II. 
• Trace Elements A group of chemical elements that are needed in minute quantities for the proper growth, development, and physiology of an organism.  
• Tranquilizing Agents A traditional grouping of drugs said to have a soothing or calming effect on mood, thought, or behavior. Included here are the ANTI-ANXIETY AGENTS , ANTIMANIC AGENTS, and the ANTIPSYCHOTIC AGENTS . These drugs act by different mechanisms and are used for different therapeutic purposes. 
• Trypanocidal Agents Agents destructive to the protozoal organisms belonging to the suborder TRYPANOSOMATINA. 
• Trypsin Inhibitors Serine proteinase inhibitors which inhibit trypsin. They may be endogenous or exogenous compounds. 
• Tubulin Modulators Agents that interact with TUBULIN to inhibit or promote polymerization of MICROTUBULES. 
• Uncoupling Agents Chemical agents that uncouple oxidation from phosphorylation in the metabolic cycle so that ATP synthesis does not occur. Included here are those IONOPHORES that disrupt electron transfer by short-circuiting the proton gradient across mitochondrial membranes. 
• Uricosuric Agents Gout suppressants that act directly on the renal tubule to increase the excretion of uric acid, thus reducing its concentrations in plasma. 
• Viscosupplements Viscoelastic solutions that are injected into JOINTS in order to alleviate symptoms of joint-related disorders such as OSTEOARTHRITIS. 
• Vitamins Organic substances that are required in small amounts for maintenance and growth, but which cannot be manufactured by the human body. 
• Voltage-Gated Sodium Channel Agonists Compounds that either stimulate the opening or prevent closure of VOLTAGE-GATED SODIUM CHANNELS. 
• Wakefulness-Promoting Agents A specific category of drugs that prevent sleepiness by specifically targeting sleep-mechanisms in the brain. They are used to treat DISORDERS OF EXCESSIVE SOMNOLENCE such as NARCOLEPSY. Note that this drug category does not include broadly-acting central nervous system stimulants such as AMPHETAMINES. 
• Water Pollutants, Chemical Chemical compounds which pollute the water of rivers, streams, lakes, the sea, reservoirs, or other bodies of water. 

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