Azathioprine is a useful therapy in patients with inflammatory bowel disease that is difficult to control. However, 10% of patients are unable to tolerate azathioprine, and the best form of treatment for this group of patients is unknown. The azathioprine metabolite 6-mercaptopurine may be a useful therapy for these patients.


To review our clinical experience of the use of the 6-mercaptopurine in inflammatory bowel disease patients who are intolerant of azathioprine.


All patients who were prescribed 6-mercaptopurine in a 2-year period were identified from pharmacy records. The case notes were reviewed and those who had previously been intolerant of azathioprine were included.


A total of 19 with either ulcerative colitis and Crohn’s disease were included. The reasons for discontinuing azathioprine were side-effects (13 patients), failure of efficacy (four patients) and leucopenia (two patients). Eleven of the 19 patients (68%) tolerated 6-mercaptopurine, including seven out of 13 patients (54%) who discontinued azathioprine due to side-effects. The length of follow-up of patients on 6-mercaptopurine was between 126 and 780 days (median 390 days).


6-mercaptopurine should be considered in patients with inflammatory bowel disease who require continuing immunosuppressive therapy, but are intolerant of azathioprine.