Which combination is often used to extend levodopa's effect in Parkinson's disease therapy?

Which combination is often used to extend levodopa's effect in Parkinson's disease therapy?

• A. Tolcapone
• B. Selegiline
• C. Amantadine
• D. Carbidopa

Answer: (A)

Extending levodopa’s effect relies on blocking its peripheral breakdown so more drug reaches the brain and stays active longer. A COMT inhibitor does exactly this by preventing levodopa from being converted to 3-O-methyllevodopa in the periphery, which increases the amount that enters the brain and smooths motor fluctuations. Tolcapone, as a COMT inhibitor, is commonly added to levodopa therapy to prolong its central effect and reduce wearing-off, though it requires liver function monitoring due to potential toxicity. Other options involve different mechanisms (MAO-B inhibition, NMDA antagonism, or peripheral decarboxylase inhibition) and don’t extend levodopa’s duration in the same way.

Extending levodopa’s effect relies on blocking its peripheral breakdown so more drug reaches the brain and stays active longer. A COMT inhibitor does exactly this by preventing levodopa from being converted to 3-O-methyllevodopa in the periphery, which increases the amount that enters the brain and smooths motor fluctuations. Tolcapone, as a COMT inhibitor, is commonly added to levodopa therapy to prolong its central effect and reduce wearing-off, though it requires liver function monitoring due to potential toxicity. Other options involve different mechanisms (MAO-B inhibition, NMDA antagonism, or peripheral decarboxylase inhibition) and don’t extend levodopa’s duration in the same way.