A 45-year-old man with Parkinson's disease on levodopa-carbidopa develops wearing-off and on-off fluctuations after 5 years of therapy. His neurologist adds a peripheral COMT inhibitor to prolong the action of levodopa. Which drug is being added?
- A Entacapone ✓
- B Selegiline
- C Bromocriptine
- D Amantadine
Correct answer: A. Entacapone
Explanation
Entacapone is a peripheral COMT inhibitor that reduces conversion of levodopa to 3-O-methyldopa in the gut and peripheral tissues, increasing the amount of levodopa available for CNS uptake and smoothing plasma level fluctuations. It must always be used adjunctively with levodopa-carbidopa, not as monotherapy. Selegiline inhibits MAO-B, reducing dopamine breakdown in the brain. Bromocriptine is a D2 dopamine agonist used for motor fluctuations. Amantadine is an NMDA antagonist used mainly for levodopa-induced dyskinesias.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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