What is first-line treatment for Parkinson's?

• A. Dopamine receptor antagonists.
• B. MAO-B inhibitors alone.
• C. Levodopa monotherapy.
• D. Levodopa plus carbidopa.

Answer: (D)

Levodopa with carbidopa is the best first-line approach because it maximizes brain dopamine while minimizing peripheral side effects. Levodopa is the key precursor that crosses the blood–brain barrier and is converted to dopamine in the brain, replenishing the depleted dopamine in Parkinson’s. However, when taken alone, most of it is converted to dopamine outside the brain by peripheral decarboxylase, causing nausea, vomiting, low blood pressure, and other side effects, and leaving less available to enter the brain. Carbidopa inhibits this peripheral conversion, reducing those side effects and increasing the amount of levodopa that reaches the brain, so motor symptoms improve more reliably with a lower dose.

That combination therefore provides the strongest, most consistent symptom relief, which is why it’s the preferred starting therapy for many patients. In younger patients, clinicians might consider alternatives to delay long-term levodopa-related complications, but for those needing solid motor control early on, levodopa plus carbidopa is the usual first choice.