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Co-trimoxazole Desensitisation — SCE Infectious Diseases MCQ

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ModerateHIV MedicineCo-trimoxazole DesensitisationSCE Infectious Diseases

A 40-year-old man on the ID ward develops a maculopapular drug rash with eosinophilia 3 weeks after starting Co-trimoxazole for PJP prophylaxis. He has well-controlled HIV (CD4 250). What is the recommended approach to re-establishing PJP prophylaxis?

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Correct answer: B — Co-trimoxazole desensitisation using a graded oral challenge protocol — if tolerated, Co-trimoxazole can be continued at full dose

Co-trimoxazole desensitisation is well-established in HIV practice. Graded oral challenge protocols (starting with very low doses and incrementally increasing over 5–14 days) allow ~70–80% of patients who previously reacted to Co-trimoxazole to tolerate it. This is important because Co-trimoxazole provides the best PJP prophylaxis AND simultaneous Toxoplasma prophylaxis. Desensitisation should only be attempted for delayed-type hypersensitivity reactions (maculopapular rash) — NOT for SJS/TEN, DRESS, or anaphylaxis. If desensitisation fails, Dapsone (check G6PD), Atovaquone, or nebulised Pentamidine are alternatives.

Reference: BHIVA 2022 – OI guidelines; BSACI 2024 – Drug desensitisation