Cumulative experience with short- and long-term toxicity to 6-mercaptopurine in the treatment of Crohn's disease and ulcerative colitis.

BACKGROUND AND AIMS: The efficacy of 6-mercaptopurine (6-MP) in the treatment and long-term maintenance of remission of inflammatory bowel disease and prevention of recurrence after resection in Crohn's disease have been established. Concern about 6-MP toxicity remains, especially the development of neoplasm. The aim of this study is to determine the incidence of all short- and long-term toxicity by follow-up of all patients with inflammatory bowel disease treated with 6-MP over a 20-year period. MATERIALS AND METHODS: We reviewed the office and hospital records and also determined the recent status of 410 patients with inflammatory bowel disease treated with 6-MP from 1980 to 1999. All toxicity was recorded. RESULTS: There was a low incidence of early drug-related allergic reactions (3.9%) and pancreatitis (1.2%). Desensitization to either 6-MP or azathioprine is often successful with the same or the other drug. Significant leukopenia (