Azathioprine: an update on clinical efficacy and safety in inflammatory bowel disease.

Background: The approval of azathioprine (AZA) for the long-term therapy of patients with Crohn's disease in The Netherlands.

Methods: Review and update of the literature on clinical efficacy and safety of AZA in inflammatory bowel disease.

Results: AZA and its metabolite 6-mercaptopurine (6-MP) are effective in the treatment of active Crohn's disease. However, the onset of the clinical response is delayed, requiring combination with other active medication in the early phase of treatment. Maintenance therapy with AZA/6-MP is also effective in the prevention of relapses in patients with Crohn's disease in remission. Indications for AZA/6-MP therapy further include refractory, fistulizing and steroid-dependent Crohn's disease. It is not known whether or when AZA/6-MP can be withdrawn in patients in long-term remission, but most clinicians discontinue therapy after 3-5 years. Although fewer data are available, AZA/6-PM appears to be effective also in the therapy of patients with ulcerative colitis. Side effects of AZA/6-MP occur in about 15% of patients and include skin rash, pancreatitis and hepatitis, dose-related neutropenia and thrombocytopenia, and risk of increased occurrence and severity of infections. Recent data suggest that the risk of malignancy, other than colorectal cancer, is not increased. Safety in pregnancy has not been studied extensively, but no increased prevalence of birth defects has been reported.

Conclusions: AZA/6-MP therapy is efficacious in patients with active Crohn's disease, but the drug is especially valuable in the long-term treatment of patients with Crohn's disease and ulcerative colitis. Drug-related side effects are frequent and require discontinuation or dose-reduction of the AZA/6-MP therapy. Due to an increased risk of infections secondary to myelosuppression, careful follow-up is mandatory. Insufficient data are available on safety in pregnancy and on the risk of malignancies, but the limited data available in patients with inflammatory bowel disease appear to be reassuring.