Thiopurine adherence: high prevalence with low impact in UC outcomes.

Introduction Thiopurines are used as maintenance therapy in patients with ulcerative colitis (UC). There are contradictory results regarding the relationship between adherence to treatment and risk of relapse. Objectives To quantify and evaluate the trends in thiopurines prescription rates, and to determine the impact and risk factors of non-adherence. Methods Analytical, observational and retrospective study of UC patients, on thiopurines, included in the ENEIDA single-center registry from October 2017 to October 2019. We included adult patients under clinical remission at the beginning of the study on thiopurines maintenance treatment for at least 6 months before recruitment. Adherence was evaluated with an electronic pharmaceutical prescription system. Adherence was considered when 80% or more of the prescribed medication was dispensed at the pharmacy. Kaplan-Meier curves and a regression model were used to examine year-to-year treatment dispensation and identify factors associated to non-adherence. Results A total of 41 patients were included, of whom 71% were males with a mean age of 44 (14) and 26.8% were concomitantly managed with biological therapy. Overall, 22% were non-adherent to thiopurines. No predictive factors of non-adherence were identified. Adherence rate did not correlate with disease activity for two years follow-up (OR 1.6; 95CI =0.3-9.1). Left-sided colitis and concomitant biological treatment were related with disease relapses (p ≤0.01). Conclusion The adherence to thiopurines in UC patients is high (78%). Non-adherence is not related to clinical or pharmacological factors. Adherence rate was not associated with disease activity.