The most important adverse effect of azathioprine (AZA) is bone marrow toxicity (BMT). Many physicians have preferred a gradual dose increment (GDI) policy for the prevention of BMT. The aim of this study was to evaluate the efficacy of GDI for the prevention of AZA-induced BMT in inflammatory bowel disease (IBD) patients.

The medical records of IBD patients who received AZA in 6 university hospitals were reviewed. The patients were divided into two groups: the GDI group (initial dose <1.5 mg/kg, gradually increased to a therapeutic dose) and the non-GDI group (initial therapeutic dose ≥2 mg/kg).

A total of 308 patients were enrolled (male to female ratio, 1:2.3; mean age, 34.91±14.19 years; ulcerative colitis, 43.5%; Crohn's disease, 55.2%; and intermediate colitis, 1.3%). The overall incidence of BMT was 16.2% (50/308). BMT developed most frequently between fourth to eighth week (26%, 13/50). The rate of BMT of the non-GDI group was significantly higher than that of the GDI group (27.5%, 11/40 vs. 14.6%, 39/268, P =0.038). A multivariate analysis showed that the only factor related to BMT was a non-GDI policy ( P =0.036; odds ratio, 2.41; 95% confidence interval, 1.06-5.49).

A GDI policy could be useful for reducing AZA-induced BMT in Korean IBD patients.