Adverse effects of azathioprine in the treatment of inflammatory bowel disease

To know the type, frequency and time course for the occurrence of adverse events in our series of patients with inflammatory bowel disease treated with azathioprine or 6-mercaptopurine.

92 consecutive patients were treated with azathioprine. 70 of them (55 Crohn's disease, 14 ulcerative colitis and 1 undetermined colitis) were suitable for analysis.

We observed 23 adverse reactions in 21 patients. Adverse events were as follows: haematological 11.4%, digestive intolerance 11.4%, infection 7.1%, and pancreatitis 2.8%. The prevalence was increased among ulcerative colitis patients (57.8 vs. 21.8%) (p = 0.02). There were no statistical differences in the prevalence of adverse events respective of the age, gender or location of disease. Digestive intolerance and pancreatitis occurred within the first 6 months of therapy, whereas haematological side effects occurred between 3 months and 4 years after therapy onset. Early occurrence (but not late occurrence) was associated with thiopurine methyltransferase (TMPT) activity levels. All infections took place between 8 months and 5 years of treatment. Azathioprine was definitively withdrawn due to side effects in 9 cases (12.8%).

The frequency of adverse events in our study is similar to that reported in previous studies. Azathioprine withdrawal is required in almost half of the cases because of toxicity. Frequency of side effects is increased in patients with ulcerative colitis. The variability in time course makes clinical-biological monitoring mandatory.