Medications & Pharmacology: What is the Classification of Antiparkinson?

October 12, 2025 •

3 min read

Parkinson's disease is primarily characterized by the loss of dopamine-producing neurons in the brain, leading to a deficiency of this vital neurotransmitter. The classification of antiparkinsonian drugs is based on how they address this imbalance by either supplementing dopamine, preventing its breakdown, or managing other neurotransmitter systems.

Quick Summary

Antiparkinsonian drugs are categorized by their mechanism of action, addressing the dopamine-acetylcholine imbalance in the brain. Primary classes include dopaminergic agents, enzyme inhibitors, anticholinergics, and glutamatergic modulators like amantadine.

Key Points

Dopaminergic agents: These drugs, including levodopa/carbidopa and dopamine agonists, directly replace or mimic the action of the deficient neurotransmitter dopamine in the brain.
Enzyme inhibitors: This class includes MAO-B and COMT inhibitors, which increase dopamine availability by preventing its enzymatic breakdown.
Anticholinergics: These agents block the activity of acetylcholine to help control tremor and rigidity, though they are used with caution due to side effects.
Amantadine: This antiviral drug increases dopamine release and blocks glutamate receptors, and is particularly useful for treating levodopa-induced dyskinesia.
Combination therapy: Most patients require a combination of antiparkinsonian drugs as the disease progresses to achieve optimal symptom control and manage motor fluctuations.
Risk-benefit profile: Each drug class has a unique profile of efficacy and potential side effects, with clinicians carefully weighing benefits against risks, especially in older patients.

Parkinson's disease is a progressive neurodegenerative disorder caused by the degeneration of dopamine-producing neurons in the substantia nigra of the brain. This dopamine deficiency results in characteristic motor symptoms such as resting tremor, rigidity, bradykinesia (slowness of movement), and postural instability. The primary goal of antiparkinsonian medications is to restore the balance of neurotransmitters, mainly dopamine and acetylcholine, to manage these motor symptoms effectively. The broad classification of these drugs is based on their mechanism of action and the neurotransmitter systems they target.

Dopaminergic Agents

This is the most common and effective class of medications for treating Parkinson's symptoms, focused on replacing or mimicking the effects of dopamine.

Dopamine Precursors

These medications are converted into dopamine in the brain. Levodopa is the most potent and effective of all antiparkinsonian drugs.

Levodopa/Carbidopa: Levodopa crosses the blood-brain barrier and is converted to dopamine. Carbidopa is added to prevent the peripheral breakdown of levodopa, increasing its availability to the brain and reducing side effects. Common formulations exist.

Dopamine Agonists

These drugs directly stimulate dopamine receptors, mimicking dopamine's effects. They have a longer duration than levodopa and are used to delay levodopa or manage motor fluctuations.

Examples: Pramipexole, Ropinirole, and Rotigotine. They can be oral or patch.

Enzyme Inhibitors

These agents increase dopamine availability by preventing its breakdown and are typically adjuncts to levodopa.

Monoamine Oxidase B (MAO-B) Inhibitors

These drugs inhibit the enzyme that breaks down dopamine, increasing its availability.

Examples: Selegiline, Rasagiline, and Safinamide. They can be monotherapy or an adjunct to reduce "off" time.

Catechol-O-methyltransferase (COMT) Inhibitors

COMT inhibitors prevent the breakdown of levodopa before it reaches the brain, prolonging its effect.

Examples: Entacapone, Opicapone, and Tolcapone. Tolcapone is less common due to potential liver toxicity.

Nondopaminergic Agents

These medications affect other neurotransmitter systems to manage specific symptoms.

Anticholinergics

These drugs block acetylcholine's action and are most effective for tremor and rigidity.

Examples: Benztropine and Trihexyphenidyl. Their use is limited due to side effects, especially in older adults.

Amantadine

Originally antiviral, amantadine has antiparkinsonian properties by increasing dopamine release and blocking NMDA receptors.

Primary Use: Amantadine is effective for reducing levodopa-induced dyskinesia and can help with tremor.

Other Classes

Adenosine A2A Antagonists: Istradefylline blocks adenosine receptors to reduce "off" time.
Miscellaneous: Some antipsychotics like Pimavanserin are used for psychosis, targeting serotonin receptors.

Comparison of Major Antiparkinsonian Drug Classes


Drug Class	Mechanism of Action	Primary Symptom Benefit	Typical Use Stage	Key Side Effects
Levodopa	Converted to dopamine	All motor symptoms	All stages	Nausea, dyskinesia, motor fluctuations
Dopamine Agonists	Directly stimulate dopamine receptors	Early motor symptoms, reduce "off" time	Early stages, or adjunct in advanced	Hallucinations, sleepiness, impulse control disorders
MAO-B Inhibitors	Block breakdown of dopamine	Mild early symptoms, extend levodopa effect	Early monotherapy, adjunct therapy	Insomnia, hallucinations (less than agonists), drug interactions
COMT Inhibitors	Block peripheral breakdown of levodopa	Extend levodopa duration, reduce "off" time	Adjunct to levodopa only	Dyskinesia, diarrhea, liver toxicity (Tolcapone)
Anticholinergics	Block action of acetylcholine	Tremor and rigidity	Early stages, or for drug-induced parkinsonism	Dry mouth, confusion, urinary retention
Amantadine	Increases dopamine release, blocks NMDA receptors	Levodopa-induced dyskinesia, tremor	Early stages, or for dyskinesia	Confusion, hallucinations, swelling, skin discoloration

Conclusion

Antiparkinsonian medications are a diverse group of drugs that address neurotransmitter imbalances in Parkinson's disease, primarily dopamine deficiency. They are classified based on their mechanisms, including dopaminergic agents, enzyme inhibitors, anticholinergics, and other agents. As the disease progresses, combination therapy is often used to manage symptoms and motor fluctuations, with careful consideration of side effects. Research continues to seek therapies with better side effect profiles and potential disease modification.

Parkinson's Foundation: Medication Class Information

Frequently Asked Questions

Levodopa is a precursor converted into dopamine in the brain and is highly effective for motor symptoms, but its effects can be short-lived. Dopamine agonists directly stimulate dopamine receptors and have a longer duration of action, often used earlier or as an adjunct therapy.

Carbidopa is combined with levodopa to prevent the breakdown of levodopa in the bloodstream by the DOPA decarboxylase enzyme, allowing more levodopa to reach the brain and reducing side effects like nausea.

MAO-B inhibitors are used in early Parkinson's as a monotherapy to delay the need for levodopa. They are also used as an add-on therapy with levodopa to help reduce "off" time (periods when medication effects wear off).

COMT inhibitors are always used alongside levodopa. They work by blocking the COMT enzyme, which degrades levodopa, thereby extending the duration of levodopa's effect in the brain and reducing motor fluctuations.

Anticholinergics are most effective for controlling prominent tremors and rigidity, particularly in younger patients. Their use is limited in older individuals due to the risk of side effects like confusion and memory issues.

Amantadine is mainly used to manage levodopa-induced dyskinesia, the involuntary movements that can occur with long-term levodopa use. It can also help with tremor.

Some antiparkinsonian medications, particularly dopamine agonists and higher doses of levodopa or amantadine, can cause hallucinations and psychosis by overstimulating dopamine pathways or affecting other brain chemistry.