A 62-year-old man with Parkinson's disease on levodopa/carbidopa develops sudden-onset episodes where his medications 'wear off' before the next dose, with increasing off-time despite dose adjustments. Which strategy is specifically approved to EXTEND ON-time in Parkinson's motor fluctuations?
- A Increasing carbidopa dose without changing levodopa
- B Adding a selective MAO-B inhibitor (rasagiline or safinamide) ✓
- C Adding amantadine to reduce dyskinesias
- D Switching to immediate-release levodopa every 8 hours
Correct answer: B. Adding a selective MAO-B inhibitor (rasagiline or safinamide)
Explanation
MAO-B inhibitors (rasagiline, selegiline, safinamide) inhibit monoamine oxidase B, reducing dopamine catabolism in the striatum and thus extending the effect of each levodopa dose — decreasing off-time by approximately 1-1.5 hours (PRESTO, LARGO trials). COMT inhibitors (entacapone, opicapone) also reduce off-time by blocking peripheral levodopa breakdown. Adding amantadine specifically targets dyskinesias, not off-time. Increasing carbidopa only reduces nausea without affecting motor fluctuations. Immediate-release levodopa q8h would worsen off-time.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.