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Methotrexate Toxicity — SCE Dermatology MCQ

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ModerateDermatopharmacologyMethotrexate ToxicitySCE Dermatology

A 45-year-old man with extensive plaque psoriasis on Methotrexate has developed mouth ulcers, malaise, and pancytopenia (WBC 1.2 × 10⁹/L, Hb 85 g/L, platelets 45 × 10⁹/L). His most recent Methotrexate dose was 3 days ago. What is the most important immediate action?

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Correct answer: E — Stop Methotrexate, give IV folinic acid (Calcium folinate), and arrange urgent haematology review

Methotrexate-induced pancytopenia is a medical emergency with significant mortality. Immediate management includes: stop Methotrexate, administer IV folinic acid (Calcium folinate — NOT folic acid, which is the inactive form) as a rescue agent to counteract folate antagonism, urgent haematology referral, supportive care (broad-spectrum antibiotics if febrile, platelet transfusion if bleeding), and investigation for precipitants (renal impairment, drug interactions — particularly Trimethoprim/Co-trimoxazole which inhibit folate metabolism, or dose errors). The NPSA patient safety alert emphasises weekly dosing, never daily.

Reference: BAD 2016 Methotrexate Guidelines; NPSA 2020 Alert; BNF