Patch testing in non‐immediate hypersensitivity to cotrimoxazole: Is it useful?

Abstract

BackgroundExisting literature has questioned the sensitivity of patch testing (PT) with cotrimoxazole (CTX) in the study of drug hypersensitivity.ObjectivesAssess the sensitivity of PT with CTX in non‐immediate cutaneous adverse drug reactions (CADR).Patients/Materials/MethodsRetrospective analysis (2000–2022) of PT with an antibiotic series including CTX 10% pet (Chemotechnique Diagnostics©) performed according to ESCD guidelines in patients with suspected non‐immediate CADR reactions to CTX. Some patients were additionally tested with in‐house preparations of CTX from Bactrim DS® tablets at 10% in pet or water and trimethoprim 10% pet (Laboratórios Edol©).ResultsSixty‐four patients (48F/16M; mean age 47 ± 18) were included, mostly with maculopapular exanthema (51, 80%). Notably, CTX was sole suspect in 24 patients. There was no positive reaction to CTX at 10% from Chemotechnique or Bactrim DS® tablets prepared at 10% pet for patch testing. One patient reacted exclusively to trimethoprim with 1+ reaction. Two patients had a faint reaction (1+) only with the powder of Bactrim DS® tablets in water at D2, but as the reactions faded completely in 24 or 48 h, they were interpreted as irritant non‐specific reactions.ConclusionThese findings suggest that patch testing may lack sufficient sensitivity to diagnose CTX‐induced non‐immediate CADR. Therefore, clinicians should be cautious interpreting CTX patch test results.