Patterns of 6-mercaptopurine and azathioprine maintenance therapy among a cohort of commercially insured individuals diagnosed with Crohn's disease in the United States.

Background And Aims: Thiopurines, including 6-mercaptopurine (6-MP) and azathioprine (AZA), are the mainstay of maintenance therapy for Crohn's disease (CD). However, studies examining their effectiveness in routine practice among diverse patient populations are lacking. Among a cohort of new users of 6MP/AZA, we described treatment patterns and changes in subsequent therapy.

Methods: Using the Truven Health Analytics databases, we identified all individuals diagnosed with CD and initiating 6-MP/AZA monotherapy from 2001-2008 (n=3,657). We estimated the proportion of CD patients remaining on 6-MP/AZA monotherapy, using Kaplan-Meier methods, and identified predictors of treatment noncontinuation, using multivariable Cox regression. Among the "noncontinuers," we described subsequent patterns of maintenance therapy and summarized the diagnosis and procedure codes and prescription drug claims preceding treatment discontinuation.

Results: The 1-year 6-MP/AZA treatment continuation rate was 42%. Children (age ≤18 years) and individuals with no prior anti-tumor necrosis factor (TNF) use were more likely to continue 6-MP/AZA, while those dispensed more (>4) outpatient prescriptions for any drug before initiation of 6-MP/AZA were less likely to continue maintenance treatment. Overall, 1,128 (39%) and 105 (4%) individuals experienced a clinical event potentially indicating active disease or 6-MP/AZA-intolerance prior to discontinuation, respectively. Most patients discontinued therapy; among the remaining patients who failed to continue 6-MP/AZA, most augmented with an anti-TNF.

Conclusion: Most patients initiating 6-MP/AZA monotherapy did not continue beyond 1 year. In contrast to trial evidence showing 1-year remission rates of 40%-80%, this study observed a lower effectiveness of 6-MP/AZA treatment, possibly due to differences in disease severity, patient demographics, comorbidity, adherence, and health care utilization.