Is neutropenia required for effective maintenance of remission during azathioprine therapy in inflammatory bowel disease?

BACKGROUND: Azathioprine is an effective treatment for maintaining remission in inflammatory bowel disease (IBD). It is a matter of debate as to whether neutropenia is required during azathioprine therapy to achieve more effective disease remission. We evaluated whether neutropenia during azathioprine therapy reduced relapse rates in IBD patients. PATIENTS AND METHODS: This retrospective study was based on a total of 173 IBD (96 Crohn's disease (CD), 77 ulcerative colitis (UC)) patients who were stable on azathioprine for a minimum of 6 months. Median duration of follow-up was 4.0 years (range 0.6-21 years). The lowest neutrophil counts during treatment for these patients were recorded. Relapse rates per year of follow-up were compared in non-neutropenic patients (neutrophil count > 2.5 x 10(9), n = 129) and neutropenic patients (neutrophil count < or = 2.5 x 10(9), n = 44) groups, and survival curves for cumulative remission rates compared by log-rank test.
RESULTS: Mean relapse rate per year of follow-up for the non-neutropenic group was 0.19/year (SD = 0.37/year) compared with the neutropenic group 0.28/year (SD = 0.43/year) (P = NS). Analysis was performed on UC and CD subgroups, and relapse rates were not significantly different. The cumulative remission per cent determined by Kaplan-Meier survival analysis showed no difference between non-neutropenic and neutropenic groups by log-rank analysis, for UC and CD as well as for all IBD patients.
CONCLUSION: Neutropenia < or = 2.5 x 10(9) while on azathioprine does not reduce the relapse rates of IBD patients who were established on azathioprine therapy compared with neutrophil counts > 2.5 x 10(9).