Carbidopa

Key facts

• Carbidopa is combined with levodopa (as in Sinemet and similar products) to treat Parkinson's disease. It blocks the breakdown of levodopa outside the brain, so a lower dose reaches the brain to become dopamine.
• It is taken several times a day on a schedule that balances symptom control against wearing-off periods; a high-protein meal can slow absorption.
• Never stop carbidopa-levodopa suddenly. Rapid withdrawal can cause a fever, severe muscle rigidity, and confusion similar to neuroleptic malignant syndrome, a medical emergency.
• Seek urgent care for high fever with stiff muscles, sudden severe confusion, or fainting with an irregular heartbeat.

What carbidopa treats

Carbidopa itself does not treat Parkinson's disease; it is added to levodopa to make that treatment work better. The combination treats the tremor, muscle rigidity, and slowed movement of Parkinson's disease, and can reduce "off" periods when symptoms return between doses.

How carbidopa works

Levodopa is converted into dopamine, the chemical Parkinson's disease depletes in the brain. Left alone, much of that conversion happens in the bloodstream before levodopa reaches the brain, causing nausea and leaving less available where it's needed. Carbidopa blocks the enzyme that converts levodopa outside the brain, so more levodopa crosses into the brain to become dopamine there.

Before you take it

• Do not combine carbidopa-levodopa with a nonselective MAO inhibitor; the combination can cause a dangerous rise in blood pressure. Stop such medicines at least two weeks beforehand.
• Tell your prescriber about a history of melanoma or unexplained skin lesions. Levodopa has been linked to melanoma activation, so periodic skin checks are recommended during treatment.
• Report any new compulsive gambling, shopping, or sexual behaviour, and any sudden episodes of falling asleep without warning, including while driving.
• Caution is needed with narrow-angle glaucoma, severe heart disease, and psychotic illness, since the medicine can worsen hallucinations or confusion.

Side effects

Common effects include nausea, dizziness on standing, dry mouth, and involuntary movements (dyskinesia) that can develop with long-term use.

Stop and seek urgent medical care for any of these:

• High fever with severe muscle stiffness and confusion.
• Sudden, severe hallucinations or confusion.
• Fainting or an irregular heartbeat.
• Severe allergic reaction: swelling of the face or throat, or difficulty breathing.

Safety essentials

• Never stop this medicine abruptly. Withdrawal can trigger a fever, rigidity, and confusion reaction resembling neuroleptic malignant syndrome, so any dose reduction must be tapered by a doctor.
• Have periodic skin examinations to check for melanoma, given the documented association with levodopa treatment.
• Avoid nonselective MAO inhibitors, and tell every prescriber you take carbidopa-levodopa before starting a new medicine.

This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.