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# Dopaminergic antiparkinson agents (levodopa and amantadine)

Medicines that restore dopamine signalling in the brain in Parkinson disease. Levodopa, given with a decarboxylase inhibitor, is the most effective.

Updated 2026-11-01

## What they are

Parkinson disease is caused by the loss of dopamine neurons of the substantia nigra. Dopamine itself does not cross the blood-brain barrier, so its precursor levodopa is given, always combined with a peripheral decarboxylase inhibitor (carbidopa or benserazide). Amantadine, an old antiviral, is grouped here because it increases dopamine release and blocks NMDA receptors; it is mainly used for levodopa-induced dyskinesia.

## Mechanism of action

Levodopa enters the brain through amino acid transporters and is converted to dopamine by aromatic L-amino acid decarboxylase in the surviving nerve terminals. Carbidopa and benserazide block that enzyme outside the brain only, so more levodopa reaches the brain and less dopamine is made in the blood (less nausea and hypotension).

Target: Dopamine synthesis (DOPA decarboxylase) and dopamine receptors; NMDA receptors (amantadine)

## Key points

- Carbidopa inhibits peripheral DOPA decarboxylase and does not cross the blood-brain barrier: more levodopa reaches the brain and peripheral side effects such as nausea fall.
- Long-term levodopa brings motor fluctuations («wearing-off» at the end of each dose, sudden «on-off» swings) and dyskinesias (involuntary writhing movements).
- Nonselective MAO inhibitors are contraindicated with levodopa (hypertensive reactions); selective MAO-B inhibitors may be combined.
- Dopamine-blocking antipsychotics and metoclopramide oppose levodopa; protein-rich meals and iron reduce its absorption.
- Stopping levodopa suddenly can cause a syndrome resembling neuroleptic malignant syndrome (fever, rigidity, confusion).

## Drugs in this class

- [**Levodopa + carbidopa** The most effective treatment for Parkinson symptoms. Levodopa becomes dopamine in the brain; carbidopa stops it being… Aromatic L-amino acid decarboxylase (DOPA decarboxylase)](https://durgical.com/en/pharmacology/levodopa-carbidopa/)
- [**Levodopa + benserazide** The other levodopa combination, common outside the US. Benserazide plays the same role as carbidopa: it stops levodopa… Aromatic L-amino acid decarboxylase (DOPA decarboxylase)](https://durgical.com/en/pharmacology/levodopa-benserazide/)
- [**Amantadine** An old antiviral that helps Parkinson disease, mainly levodopa-induced dyskinesia. It is cleared by the kidney and can… NMDA glutamate receptor (channel pore)](https://durgical.com/en/pharmacology/amantadine/)

## Others in the class

- Levodopa + carbidopa + entacapone
- Foslevodopa + foscarbidopa
- Levodopa inhalada

## Test yourself

Think of the answer, then tap the question to see it.

## Why is levodopa given instead of dopamine?

Dopamine does not cross the blood-brain barrier; levodopa does, and is converted to dopamine inside the brain.

## What does carbidopa add to levodopa?

It blocks peripheral DOPA decarboxylase, so less levodopa is lost in the blood, more reaches the brain and nausea is less.

## Which motor complications appear after years of levodopa?

Wearing-off and on-off fluctuations and dyskinesias.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 21 (McGraw Hill, 2023); Farmacología básica y clínica (Katzung), 16.ª ed., cap. 28 (McGraw Hill, 2025); [DailyMed - CARBIDOPA AND LEVODOPA tablet](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4ace5274-b6cf-414c-b9c0-f60e28a9cea5) (DailyMed (U.S. National Library of Medicine), 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=N04BA) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/classes/dopaminergic-antiparkinson-agents/