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Methotrexate toxicity — SCE Rheumatology MCQ

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HardInflammatory ArthritisMethotrexate toxicitySCE Rheumatology

A 76-year-old with eGFR 28 mL/min/1.73 m² takes colchicine prophylaxis during urate-lowering titration. Clarithromycin is prescribed for pneumonia. What is the safest medication action?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: B — Avoid the combination and choose an antibiotic without strong CYP3A4 or P-glycoprotein inhibition

Explanation lettering: D = shown as A · A = shown as B · E = shown as D · B = shown as E

A is correct. Colchicine has a narrow therapeutic index; clarithromycin inhibits CYP3A4 and P-glycoprotein, while renal impairment reduces colchicine clearance. The combination can cause fatal marrow, neuromuscular and multiorgan toxicity and should be avoided. B reverses renal pharmacokinetics. C offers an unvalidated partial adjustment for a contraindicated high-risk pairing. D increases exposure. E is ineffective because colchicine is not reliably removed by dialysis.

Reference: Colchicine 500 microgram tablets — UK SmPC: https://www.medicines.org.uk/emc/product/100968/smpc