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Sulfonamide Cross-Reactivity Myth — RACP Adult Medicine MCQ

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EasyInfectious DiseasesSulfonamide Cross-Reactivity MythRACP Adult Medicine

A 55-year-old man with a documented severe sulfonamide antibiotic allergy (TMP-SMX causing SJS) asks about safety of furosemide (a sulfonamide-containing non-antibiotic). He requires a loop diuretic for heart failure. What is the most appropriate advice?

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Correct answer: A — Furosemide is safe — no clinically significant cross-reactivity

Sulfonamide antibiotic allergy does NOT confer cross-reactivity to sulfonamide non-antibiotics (furosemide, thiazides, celecoxib, sulfasalazine). The allergenic determinant is the N1-substituted sulfonamide aromatic amine group present in sulfonamide antibiotics but absent from non-antibiotic sulfonamides. Multiple studies confirm no increased risk. The historical blanket avoidance of all sulfonamides is outdated.

Reference: ASCIA – 2024 – Drug Allergy; Wulf 2009 Sulfonamide Cross-Reactivity