Dopamine agonist

• Dopamine agonists are a class of medications that mimic the action of dopamine, a neurotransmitter in the brain.
• These agents interact with dopamine receptors and activate them, leading to various physiological responses.
• Dopamine agonists are used in the management of several medical conditions, including Parkinson's disease, hyperprolactinemia, and certain restless leg syndrome cases.

Mechanism of Action

• Dopamine agonists exert their effects by directly binding to dopamine receptors, which are part of the G-protein-coupled receptor family.
• There are five main subtypes of dopamine receptors, D1 to D5, distributed throughout the brain and peripheral tissues. Each subtype plays a distinct role in mediating different physiological functions.
• When a dopamine agonist binds to a specific dopamine receptor subtype, it activates the receptor, triggering a cascade of intracellular signaling events.
• This activation can lead to either excitatory or inhibitory responses, depending on the receptor subtype and the location in the brain or body.
• The overall effect of dopamine agonists is to increase dopamine receptor activation, effectively enhancing dopaminergic neurotransmission in targeted regions of the brain.

Clinical Applications

• Dopamine agonists find diverse applications in several medical conditions:

1. Parkinson's Disease

• In Parkinson's disease, there is a progressive loss of dopaminergic neurons in the substantia nigra region of the brain, leading to a decrease in dopamine levels.
• Dopamine agonists are used as adjunctive therapy or monotherapy to stimulate dopamine receptors and improve motor symptoms, such as rigidity, bradykinesia (slowness of movement), and tremors.

2. Hyperprolactinemia

• Hyperprolactinemia is a condition characterized by elevated levels of prolactin hormone.
• Dopamine agonists, particularly those with a high affinity for D2 receptors, are used to reduce prolactin secretion from the pituitary gland, thus normalizing prolactin levels and alleviating associated symptoms like galactorrhea (spontaneous milk production), irregular menstruation, and infertility.

3. Restless Leg Syndrome (RLS)

• RLS is a neurological disorder characterized by an irresistible urge to move the legs, often accompanied by uncomfortable sensations.
• Dopamine agonists, primarily those targeting D2 receptors, have been shown to alleviate RLS symptoms and improve sleep quality.

4. Prolactin-Secreting Pituitary Adenomas

• Prolactinomas are benign tumors of the [[]]pituitary gland that secrete excessive amounts of prolactin.
• Dopamine agonists are the first-line treatment for these tumors, as they effectively shrink the tumor and normalize prolactin levels in many cases, often avoiding the need for surgery.

Side Effects

• Despite their therapeutic benefits, dopamine agonists can also produce several side effects, which may vary depending on the specific agent and dose used:

• Nausea and Vomiting: Gastrointestinal disturbances, particularly nausea and vomiting, are common side effects of dopamine agonists. Taking the medication with food may help alleviate these symptoms.
• Orthostatic Hypotension: Some individuals may experience a drop in blood pressure upon standing, leading to dizziness or lightheadedness.
• Impulse Control Disorders: Dopamine agonists have been associated with an increased risk of impulse control disorders, such as compulsive gambling, hypersexuality, or excessive shopping.
• Hallucinations and Psychiatric Symptoms: In some cases, dopamine agonists may lead to hallucinations, psychosis, or exacerbation of existing psychiatric conditions.
• Daytime Sleepiness and Sleep Attacks: Sleep disturbances, including daytime sleepiness and sudden sleep attacks, have been reported with the use of dopamine agonists.
• Dyskinesias: Long-term use of dopamine agonists in Parkinson's disease may lead to involuntary movements known as dyskinesias.

• It's important for patients to be aware of these potential side effects and promptly inform their healthcare provider if they experience any concerning symptoms.

Contraindications

• Dopamine agonists are contraindicated in certain medical conditions due to potential risks and adverse effects.

Contraindications include:

• History of Hypersensitivity: Patients with a known hypersensitivity to any dopamine agonist or its components should avoid using these medications.
• Psychosis: Dopamine agonists can exacerbate existing psychotic symptoms or precipitate new-onset psychosis. Therefore, they are generally avoided in individuals with a history of psychosis or schizophrenia.
• Uncontrolled Hypertension: Dopamine agonists can cause vasoconstriction and may worsen hypertension. They should be used cautiously or avoided in patients with uncontrolled high blood pressure.
• Severe Cardiovascular Disease: Patients with severe cardiovascular conditions, such as severe coronary artery disease or heart failure, may experience adverse cardiovascular effects with dopamine agonist use.
• History of Impulse Control Disorders: Individuals with a history of impulse control disorders, such as compulsive gambling or hypersexuality, should exercise caution when using dopamine agonists due to the potential for exacerbation of these behaviors.

Drug Interactions

• Dopamine agonists may interact with other medications, leading to altered drug levels or increased risk of side effects.

Some significant drug interactions include:

• Dopamine Antagonists: Concomitant use of dopamine antagonists, such as typical and atypical antipsychotics, can reduce the effectiveness of dopamine agonists and may lead to a worsening of the underlying condition.
• Metoclopramide: Metoclopramide, a prokinetic agent, may antagonize the effects of dopamine agonists and should be used cautiously together.
• Monoamine Oxidase Inhibitors (MAOIs): MAOIs can potentiate the effects of dopamine agonists and may increase the risk of adverse reactions. Concurrent use of these agents requires careful monitoring.
• Antihypertensive Medications: Dopamine agonists may interact with antihypertensive medications, leading to additive hypotensive effects. Dose adjustments may be necessary in such cases.

• It is crucial for healthcare providers to review a patient's medication history thoroughly to identify potential drug interactions before prescribing dopamine agonists.

See Also

• Dopamine Receptors
• Parkinson's Disease
• Hyperprolactinemia

References

• Bédard P, Riopelle RJ. Neuroleptic-induced supersensitivity psychosis: clinical and pharmacologic characteristics. Am J Psychiatry. 1985 Jun;142(6):784-7. doi: 10.1176/ajp.142.6.784. PMID: 2863876.
• Colosimo C, Morgante L, Antonini A, et al. Non-motor symptoms in atypical and secondary parkinsonism: The PRIAMO study. J Neurol. 2010;257(1):5-14. doi:10.1007/s00415-009-5354-2.
• Ondo WG. Restless legs syndrome: pathophysiology, diagnosis and treatment. CNS Drugs. 2002;16(11):741-749. doi:10.2165/00023210-200216110-00002.
• Barone P, Poewe W, Albrecht S, et al. Pramipexole for the treatment of depressive symptoms in patients with Parkinson's disease: a randomised, double-blind, placebo-controlled trial. Lancet Neurol. 2010;9(6):573-580. doi:10.1016/S1474-4422(10)70106-X.
• Bracco F, Battaglia A, Chouza C, et al. Ropinirole in the treatment of early Parkinson's disease: a 6-month interim report of a 5-year levodopa-controlled study. Mov Disord. 1997;12(5):607-615. doi:10.1002/mds.870120503.
• U.S. Food and Drug Administration. REQUIP (ropinirole hydrochloride) Tablets for Oral use. Full prescribing information. Revised July 2021. Available at: [1]
• European Medicines Agency. Summary of Product Characteristics: Mirapexin (pramipexole). Available at: [2]
• U.S. Food and Drug Administration. MIRAPEX (pramipexole dihydrochloride) Tablets. Full prescribing information. Revised August 2020. Available at: [3]
• U.S. Food and Drug Administration. NEUPRO (rotigotine) Transdermal System. Full prescribing information. Revised November 2020. Available at: [4]
• Oertel W, Benes H, Garcia-Borreguero D, et al. Rotigotine transdermal patch in moderate to severe idiopathic restless legs syndrome: a randomized, placebo-controlled polysomnographic study. Sleep Med. 2010;11(9):848-856. doi:10.1016/j.sleep.2010.01.009.
• Lamotte G, Pérez-Lloret S, García R, et al. Dopamine agonist withdrawal syndrome: A comprehensive review. J Neurol Neurosurg Psychiatry. 2017;88(9):868-875. doi:10.1136/jnnp-2016-313570.

This article is a stub. You can help WikiMD by registering to expand it. Editing is available only to registered and verified users. WikiMD is a comprehensive, free health & wellness encyclopedia.