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Benserazide – Peripheral DDCI Role — SCE Neurology MCQ

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EasyMovement DisordersBenserazide – Peripheral DDCI RoleSCE Neurology

A 55-year-old man with recently diagnosed Parkinson's disease is started on co-beneldopa (levodopa with benserazide). He develops nausea. What is the role of the benserazide component, and how should the nausea be managed?

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Correct answer: A — Benserazide is a peripheral dopa-decarboxylase inhibitor that prevents peripheral conversion of levodopa to dopamine, reducing peripheral side effects (nausea, hypotension); nausea should be managed with domperidone (peripheral dopamine antagonist that does not cross the BBB)

Benserazide (in co-beneldopa) and carbidopa (in co-careldopa) are peripheral dopa-decarboxylase inhibitors (DDCIs). They block the enzyme aromatic L-amino acid decarboxylase in the periphery, preventing levodopa from being converted to dopamine outside the brain. This: (1) increases the amount of levodopa available to cross the BBB, (2) reduces the dose of levodopa needed, and (3) reduces peripheral dopaminergic side effects (nausea, vomiting, hypotension). Despite DDCIs, some nausea still occurs — domperidone is the antiemetic of choice as it blocks D2 receptors peripherally without crossing the BBB. A: Benserazide is a DDCI, not a DA. C: Benserazide reduces nausea, not causes it. D: MAO-B inhibitors are selegiline, rasagiline. E: COMT inhibitors are entacapone, opicapone.

Reference: NICE NG71; BNF – Co-Beneldopa