Sulfonamide Allergy in HIV — SCE Infectious Diseases MCQ

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EasyHIV MedicineSulfonamide Allergy in HIVSCE Infectious Diseases

A 28-year-old man with HIV (CD4 60) develops cerebral toxoplasmosis. He is started on Pyrimethamine plus Sulfadiazine plus Folinic Acid. At day 10 he develops severe rash with mucosal involvement and eosinophilia. What is the most likely causative drug?

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Correct answer: B — Sulfadiazine — sulfonamide hypersensitivity is common in HIV (up to 40% adverse reaction rate)

Sulfonamide hypersensitivity is extremely common in HIV-positive patients (~40% adverse reaction rate with Co-trimoxazole/Sulfadiazine vs ~3% in the general population). The mechanism involves altered drug metabolism, glutathione depletion, and immune dysregulation. Severe reactions (SJS/TEN, DRESS) require permanent discontinuation of sulfonamides. The alternative Toxoplasma regimen is Pyrimethamine plus Clindamycin plus Folinic Acid. Desensitisation protocols exist for Co-trimoxazole (for PJP prophylaxis) but are not routinely performed for Sulfadiazine in acute Toxoplasma treatment.

Reference: BHIVA 2022 – OI guidelines; BSACI 2024 – Sulfonamide allergy in HIV