Adherence to thiopurine treatment in out-patients with Crohn's disease

Background High frequency of incomplete or non-response to azathioprine (AZA) and/or mercaptopurine (MP) limit their use in Crohn's disease (CD). Non-adherence is considered to be of relevance for ineffectiveness. Aim To assess adherence to thiopurines in CD out-patients treated in a single gastroenterology practice. Methods Patients were eligible for inclusion if they received AZA/MP for at least 3 months. After follow-up of 3 months, adherence to AZA/MP was assessed by quantitation of relevant thiopurine metabolite levels in red blood cells as well as by patients' self-report using standardized questionnaire. Results Sixty-five patients were prospectively included. Six patients (9.2%) had metabolite profiles indicative of non-adherence. Self-assessed questionnaire revealed non-adherence in four of 56 patients (7.1%). Therapeutic drug monitoring (TDM) and self-assessment as two independent methods had a concordance rate of 75%. Metabolite levels and self-assessed adherence were not significantly different between patients in remission compared with those with active disease. Conclusions Out-patients with CD treated in a single gastroenterology practice had a satisfactory adherence (> 90%) to thiopurine therapy. Different measures of adherence (TDM and self-report) applied to the same patient suggest comparable levels. TDM appears to be a reliable tool to assess adherence to thiopurines in clinical practice.