Movement Disorders USMLE Step 1 Practice Question
A 73-year-old man with Parkinson disease presents with tremor, bradykinesia, and rigidity. Vital signs: BP 138/82, HR 88, RR 16, Temp 37.1°C, SpO2 98%. He was started on carbidopa-levodopa three months ago. Current examination shows significant improvement in slowness and rigidity; however, mild resting tremor persists. Levodopa level is therapeutic at 1.2 mcg/mL. Which of the following best explains carbidopa's role in optimizing this medication regimen?
Answer choices
- AIt directly stimulates dopamine receptors in the striatum
- BIt inhibits peripheral dopa decarboxylaseCorrect answer
- CIt blocks catechol-O-methyltransferase in the CNS
- DIt prevents levodopa from crossing the blood-brain barrier
- EIt inhibits MAO-B in the substantia nigra
- FIt inhibits the reuptake of dopamine at the nigrostriatal synapse
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