Paper I
2025 March (Supplementary (SAY)) (2019 Scheme) · 100 marks · 180 min

Question

Classify the drugs used in Gout. Explain the mechanism of action and adverse effects of Allopurinol. (2+4)

Q86 marksShort Essays

Answer

Classification of drugs used in gout

GroupExamples
Anti-inflammatory (acute attack)Colchicine, NSAIDs (Indomethacin), Corticosteroids
Urate-lowering — Xanthine oxidase inhibitorsAllopurinol, Febuxostat
Urate-lowering — UricosuricsProbenecid, Sulfinpyrazone
UricolyticRasburicase

Allopurinol — mechanism of action and adverse effects Mechanism: allopurinolinhibits xanthine oxidase → blocks conversion of hypoxanthine to xanthine and xanthine to uric acid → reduced uric acid synthesis, lowering serum urate levels over time. Not useful for an acute attack (can even worsen one if started during it, by mobilizing existing urate crystals); used for chronic interval/prophylactic therapy, started only after an acute attack has resolved.

Adverse effects: hypersensitivity reactions (including rare but severe Stevens-Johnson syndrome/toxic epidermal necrolysis), GI upset, hepatotoxicity, and increased toxicity of co-administered azathioprine/6-mercaptopurine (allopurinol inhibits xanthine oxidase, the enzyme that normally inactivates these drugs, requiring dose reduction if co-prescribed).

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