Paper I — 2016 October (Supplementary) (2010 Scheme) — Q4

Paper I

2016 October (Supplementary) (2010 Scheme) · 40 marks · 120 min

Question

COMT inhibitors.

Q43 marksShort Notes★✓

Answer

COMT (catechol-O-methyltransferase) inhibitors are drugs used as adjuncts to levodopa therapy in Parkinson’s disease.

Examples

• Entacapone, Tolcapone

Mechanism of action

• Inhibit COMT, the enzyme that peripherally metabolizes levodopa (and dopamine) to inactive 3-O-methyldopa
• By blocking this peripheral degradation pathway, they increase the plasma half-life and bioavailability of levodopa, allowing more levodopa to reach the brain

Uses

• Adjunct to levodopa-carbidopa in Parkinson’s disease, particularly to reduce “wearing-off” fluctuations

Adverse effects

• Diarrhoea
• Orange discolouration of urine
• Hepatotoxicity (tolcapone — requires liver function monitoring; entacapone is safer in this regard)
• Worsening of levodopa-related dyskinesias (due to increased dopaminergic effect)

Related Concepts

1. 1Antiparkinsonian Drugs

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