Elimination (pharmacology)

Diagram of a nephron, the functional unit of the kidney, which plays a crucial role in drug elimination.

In pharmacology, elimination refers to the process by which a drug is removed from the body. This process is essential for the termination of the drug's action and involves both metabolism and excretion. Elimination is a key factor in determining the half-life of a drug, which in turn influences the dosing regimen.

Metabolism

Metabolism is the chemical alteration of a drug by the body. The primary site of drug metabolism is the liver, where enzymes such as the cytochrome P450 family modify drugs to make them more water-soluble, facilitating their excretion. Metabolism can result in the activation of prodrugs, the inactivation of active drugs, or the conversion of drugs into toxic metabolites.

Excretion

Excretion is the removal of the drug from the body, primarily through the kidneys in the form of urine. Other routes of excretion include the bile, feces, lungs, and sweat. The kidneys filter the blood, reabsorb necessary substances, and excrete waste products and drugs in the urine.

Renal Excretion

The kidneys play a crucial role in drug elimination through three main processes: glomerular filtration, tubular secretion, and tubular reabsorption.

• Glomerular filtration is the process by which drugs are filtered from the blood into the renal tubule.
• Tubular secretion involves the active transport of drugs from the blood into the tubular fluid.
• Tubular reabsorption can occur when drugs are reabsorbed from the tubular fluid back into the blood, which can affect the rate of elimination.

Factors Affecting Elimination

Several factors can influence drug elimination, including:

• Age: Elderly patients may have reduced renal function, affecting drug clearance.
• Genetics: Genetic variations can affect enzyme activity and drug metabolism.
• Disease states: Conditions such as liver disease or kidney disease can impair drug elimination.
• Drug interactions: Some drugs can inhibit or induce metabolic enzymes, altering the elimination of other drugs.

Related pages

• Pharmacokinetics
• Drug metabolism
• Renal physiology
• Cytochrome P450