Thiopurine adherence: a high prevalence with low impact on 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 thiopurine prescription rates, and to determine the impact and risk factors of non-adherence.
Methods: analytical, observational, retrospective study of UC patients taking thiopurines included in the ENEIDA single-center registry from October 2017 to October 2019. Adult patients in clinical remission at the beginning of the study on thiopurines maintenance treatment for at least 6 months before recruitment were included. 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 to identify factors associated with 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 during two years of follow-up (OR 1.6; 95 % CI = 0.3-9.1). Left-sided colitis and concomitant biological treatment were related with disease relapse (p ≤ 0.01).
Conclusion: 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.