Allergic reactions to 6-mercaptopurine during treatment of inflammatory bowel disease

Hypersensitivity reactions to 6-mercaptopurine (6-MP) or azathioprine occur during the treatment of inflammatory bowel disease (IBD), raising signific ant diagnostic and therapeutic challenges. Charts of 591 patient with IBD t reated with 6-MP in a single center were retrospectively reviewed. All alle rgic reactions were recorded along with results of rechallenge, desensitiza tion, and subsequent course of IBD. Sixteen (2.7%) allergic reactions to 6- MP were noted, with fever being the most common (14 cases). Nine of these w ere rechallenged with 6-MP with recurrence of the same symptoms. Azathiopri ne was tried in six patients and in five the same symptoms recurred. Four p atients underwent successful desensitization to either 6-MP or azathioprine ; all four plus another patient who tolerated direct switch to azathioprine entered long-term remission. Among the remaining 11, 5 required surgery, 2 are well on methotrexate, and 4 have chronic symptoms while being treated with other medications. If an allergic reaction to 6-MP occurs during the t reatment of IBD, direct switching to azathioprine is probably not justified . Instead, desensitization to either 6-MP or azathioprine should be attempt ed. Patients who can tolerate these medications after previous allergic rea ctions have improved outcomes compared with patients who resort to other fo rms of treatment.