Which medication is an MAO-B inhibitor used in Parkinson disease?

• A. Levodopa
• B. Benztropine
• C. Selegiline
• D. Carbidopa

Answer: (C)

MAO-B inhibitors help Parkinson disease by preventing the breakdown of dopamine in the brain, so more dopamine remains available to stimulate receptors and improve motor function. Selegiline is an MAO-B inhibitor used in PD; by blocking MAO-B, it slows dopamine degradation and can enhance and prolong the effect of existing dopamine or of levodopa when used together. This makes it useful as add-on therapy to reduce wearing-off or, in some cases, as initial therapy in younger patients.

Levodopa is a dopamine precursor, not an MAO-B inhibitor, and is often paired with carbidopa to prevent peripheral conversion. Benztropine is an anticholinergic used to help tremor and rigidity via cholinergic-dopaminergic balance rather than by inhibiting dopamine breakdown. Carbidopa blocks peripheral metabolism of levodopa, increasing central availability, but does not inhibit MAO-B.