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Psoriasis vs PR — SCE Dermatology MCQ

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HardInflammatory DermatosesPsoriasis vs PRSCE Dermatology

A 70-kg patient has taken isotretinoin 40 mg daily for 20 weeks. Acne is clear and no new lesion has appeared for six weeks. Approximately what cumulative exposure has been reached, and what does NICE allow?

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

Reveal the answer and explanation

Correct answer: E — About 80 mg/kg; consider stopping because clearance has persisted for 4–8 weeks

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

C is correct. Twenty weeks is 140 days; 40 mg daily gives 5,600 mg, and 5,600/70 equals 80 mg/kg. NICE generally continues towards a cumulative 120–150 mg/kg, but permits earlier stopping after an adequate response with no new lesions for 4–8 weeks. This patient has been clear for six weeks, so stopping can be considered despite the lower cumulative exposure. The alternative calculations are arithmetically wrong, and treating to an exact cumulative number regardless of sustained clearance ignores the NICE exception.

Reference: NICE NG198: acne vulgaris management: https://www.nice.org.uk/guidance/ng198/chapter/Recommendations