What are the effects of dopamine agonist and antagonist drugs?

From the Guidelines

Dopamine agonists and antagonists have distinct effects on dopamine signaling in the brain, with agonists mimicking dopamine's effects and antagonists blocking dopamine receptors, and their use should be carefully considered based on the individual patient's condition and the potential risks and benefits, as evidenced by recent studies 1. The effects of dopamine agonist and antagonist drugs can be understood by examining their mechanisms of action. Dopamine agonists, such as pramipexole (Mirapex), ropinirole (Requip), and bromocriptine (Parlodel), bind to and activate dopamine receptors, mimicking the effects of dopamine in the brain. These medications are commonly used to treat Parkinson's disease, restless legs syndrome, and certain types of pituitary tumors, with dosages ranging from 0.125-4.5 mg/day for pramipexole, 0.25-24 mg/day for ropinirole, and 2.5-40 mg/day for bromocriptine. On the other hand, dopamine antagonists, such as haloperidol (0.5-5 mg twice daily), risperidone (2-8 mg/day), and olanzapine (5-20 mg/day), block dopamine receptors, preventing dopamine from binding and reducing excessive dopamine activity that contributes to hallucinations and delusions in conditions like schizophrenia, bipolar disorder, and other psychotic conditions. Key points to consider when using these medications include:

• The potential for significant side effects, such as impulse control disorders and nausea with agonists, and movement disorders and metabolic changes with antagonists
• The need for individualized dosing and careful monitoring by healthcare providers
• The importance of considering the patient's overall condition, including any comorbidities or potential interactions with other medications
• The potential for augmentation of symptoms with dopamine agonists, as noted in a recent study 1, which highlights the need for careful management and potential alternatives, such as iron treatment or alpha-2-delta ligands.

From the FDA Drug Label

Ropinirole tablets are dopamine agonist medicines Dopamine agonist medicines, including ropinirole tablets can cause withdrawal symptoms as your dose is slowly lowered (tapered) or when treatment with ropinirole tablets is stopped RISPERIDONE may antagonize the effects of levodopa and dopamine agonists.

The effects of dopamine agonist drugs, such as ropinirole, include:

• Withdrawal symptoms when the dose is lowered or stopped
• Increased risk of hallucinations and other psychotic-like behavior
• Uncontrolled sudden movements
• Unusual urges, such as an unusual urge to gamble or increased sexual urges
• Falling asleep during normal activities
• Decrease in blood pressure (hypotension)
• Increase in blood pressure

The effects of dopamine antagonist drugs, such as risperidone, include:

• Antagonism of dopamine agonists, such as levodopa
• Enhancement of hypotensive effects of other therapeutic agents
• Centrally-acting effects, which may be increased when taken with other centrally-acting drugs and alcohol 2

From the Research

Effects of Dopamine Agonist Drugs

• Dopamine agonists are effective in treating restless legs syndrome (RLS) and periodic limb movements (PLMs) 3, 4, 5.
• They are also used to treat Parkinson's disease, improving motor symptoms and addressing non-motor symptoms 6.
• Dopamine agonists have been shown to alleviate RLS symptoms in 70-100% of patients 3, 4.
• Examples of dopamine agonists used to treat RLS include pergolide, pramipexole, ropinirole, and cabergoline 3, 4, 5.
• Dopamine agonists have a longer half-life and lower likelihood of augmentation compared to levodopa, making them a preferred treatment option for RLS 3, 4.

Effects of Dopamine Antagonist Drugs

• Dopamine antagonists are used to treat nausea, psychosis, and acute migraine 7.
• They are also used in the emergency room setting for migraine, especially for patients with nausea and vomiting 7.
• Neuroleptics, including antipsychotics, act as antagonists at the dopamine D2 receptor type and have variable activity as antihistamines and anticholinergics 7.
• Dopamine antagonists can cause adverse events such as sedation, akathisia, dystonic reactions, neuroleptic malignant syndrome, or movement disorders with long-term use 7.

Comparison of Dopamine Agonist and Antagonist Drugs

• Dopamine agonists and antagonists have different mechanisms of action and are used to treat different conditions 7, 3, 6, 4, 5.
• Dopamine agonists are generally used to treat conditions such as RLS and Parkinson's disease, while dopamine antagonists are used to treat conditions such as nausea, psychosis, and migraine 7, 3, 6, 4, 5.
• The choice of dopamine agonist or antagonist depends on the specific condition being treated and the individual patient's needs 7, 3, 6, 4, 5.