Hypersensitivity to azathioprine mimicking gastroenteritis. Absence of recurrence with 6-mercaptopurine.

Hypersensitivity mimicking gastroenteritis is a rare complication of azathioprine therapy for which the mechanism is unknown. We report a case of devastating diarrhoea and vomiting due to azathioprine treatment in which hypersensitivity to the imidazole moiety of azathioprine was demonstrated. This has important therapeutic implications: in this situation, 6-mercaptopurine, which is the portion of azathioprine responsible for the cytotoxic therapeutic effect, can be administered without recurrence of side-effects.