Known brand names include Sinemet, Rytary, Crexont, Duopa, Dhivy, and Vyalev.
The main oral treatment for Parkinson's disease. Levodopa is turned into dopamine in the brain, and carbidopa keeps it from being used up in the rest of the body. It eases slowness, stiffness, and tremor, but involuntary movements, wearing off between doses, low blood pressure on standing, and hallucinations can develop.
Carbidopa-levodopa works on Parkinson's symptoms, which come from a loss of dopamine in a movement area deep in the brain. Dopamine itself cannot get into the brain, but levodopa can, and the brain turns it into dopamine. Carbidopa blocks the enzyme that makes this change in the rest of the body, and it does not enter the brain itself. That leaves more levodopa free to reach the brain, so much smaller doses work.
Levodopa that turns into dopamine outside the brain causes nausea, so the combination causes less nausea and vomiting than levodopa alone. Carbidopa also makes levodopa last longer in the blood, about 1.5 hours instead of about 50 minutes, and the tablet starts releasing its ingredients within 30 minutes. The effect can wear off toward the end of each dose, and a high-protein diet or iron supplements can lower how much levodopa is absorbed. Drugs that raise dopamine activity in the brain are linked to falling asleep suddenly and to intense urges, such as to gamble.
Carbidopa-levodopa treats Parkinson's disease, a brain disease that worsens over time and causes tremor at rest, stiffness, and slow movement. It also treats parkinsonism, the same kind of movement symptoms, when it follows a brain infection (encephalitis) or carbon monoxide or manganese poisoning. It helps people move more easily, and it controls the disease without curing it.
It comes as a tablet taken by mouth at regular times through the day, and the full benefit can take several months to appear. Adding carbidopa lets people take much less levodopa and causes less nausea than levodopa alone. It is not recommended for anyone under 18, since its safety and benefit in children have not been shown. It must not be combined with nonselective MAO inhibitors or used by people with narrow-angle glaucoma.
Involuntary movements and nausea are the most common side effects, along with dizziness or fainting when standing up, sleepiness, and dark saliva, urine, or sweat. The label warns about falling asleep suddenly during everyday activities such as driving, hallucinations and confusion, intense urges to gamble, spend, eat, or have sex, depression with suicidal thoughts, and seizures from low vitamin B6. It also warns that cutting the dose suddenly can cause a dangerous reaction with high fever and rigid muscles.