Levodopa (INN) or L-DOPA (3,4-dihydroxy-L-phenylalanine) is an intermediate in dopamine biosynthesis. Clinically, levodopa is used in the management of Parkinson's disease.

Therapeutic use

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Levodopa is used as a prodrug to increase dopamine levels for the treatment of Parkinson's disease, since it is able to cross the blood-brain barrier whereas dopamine itself cannot. Once levodopa has entered the central nervous system (CNS), it is metabolised to dopamine by aromatic-L-amino-acid decarboxylase. However, conversion to dopamine also occurs in the peripheral tissues, causing adverse effects and decreasing the available dopamine to the CNS, so it is standard practice to co-administer a peripheral DOPA decarboxylase inhibitor – carbidopa or benserazide – and often a catechol-O-methyl transferase (COMT) inhibitor.

Adverse effects

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Possible adverse drug reactions include:

• Hypotension, especially if the dosage is too high.
• Arrhythmias, although these are uncommon.
• Nausea, which is often helped by taking the drug with food, although protein interferes with drug absorption.
• Gastrointestinal bleeding.
• Disturbed respiration. This is not always harmful, and can actually benefit patients with upper airway obstruction.
• Hair loss.
• Confusion.
• Extreme emotional states, particularly anxiety, but also excessive libido.
• Vivid dreams and/or fragmented sleep.
• Visual and possibly auditory hallucinations.
• Effects on learning. There is some evidence that it improves working memory, while impairing other complex functions.
• Sleepiness and sleep attacks.
• a condition similar to amphetamine psychosis.

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