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P-038 Differentiating Oral Mesalamine Adherence Patterns in Ulcerative Colitis Patients: A Group-Based Trajectory Model Approach

Background:Long-term adherence to mesalamine (5-ASA) is important for the prevention of relapse and for protection against suboptimal outcomes in patients with ulcerative colitis (UC). This study examines the association of baseline covariates with classification into 6 adherence subgroups. Methods:Longitudinal group-based trajectory modeling was used to identify subpopulations of patients with UC (ICD-9 = 556.x) who have similar oral 5-ASA adherence patterns during a 12-month period following an initial oral 5-ASA (index) filling. Monthly adherence was measured using prescription claims from the Truven Health Marketscan Database. Covariates in a multinomial logistic regression model were used to identify significant predictors within each trajectory group. Predictor variables include age, sex, geographic region, rural residence, type of health plan, insurance type, mail-order status, comorbidities, prescription characteristics, and other UC treatments during the 6-month, pre-index period. Results:Initial models show that a 6-group trajectory model best fits the UC data over the 12-month observation period, which demonstrates high measured adherence, complete non-adherence, and 4 intermediate groups that shift across the study period. The most adherent group demonstrates over 80% Proportion of Days Covered (PDC) for each of the 12 months observed, and encompasses 15.3% of the sample. A sizeable group (23.4%) is mostly non-adherent for the study period, with an initial fill and then nearly no refilled prescriptions over the study period (group 6). The smallest group of 9.2% is likely adjusting their medication dosages as they continue to fill their prescriptions throughout the study period (group 3).Characteristics that significantly (P <0.05) differentiate the group with the highest adherence from the group with the lowest adherence (reference group) include age, sex, geographic region, HMO insurance type, mail-order status, 30-day supply, less than a $20 copay, presence of cerebrovascular disease, once-daily 5-ASA (index fill), and non–immune modulator therapy during the pre-index period. Contrary to other published models, the total number of non–5-ASA fillings, rural residents, health plans, and 5-ASA copays (index fill) did not significantly differentiate the highest adherence group from the lowest. Conclusions:Group-based trajectory methods allow researchers to distinguish intermediate adherence subgroups that exist among people who might otherwise be labeled as non-adherent, and provides a more detailed representation of the ways in which patients are managing their medications. Adherence to 5-ASA treatment for UC patients is typically low, as demonstrated in prior studies, and is associated with increased flares, hospitalizations, emergency department visits, and missed work days. Using group-based trajectory modeling to assess long-term medication adherence for UC patients, we found that adherence to 5-ASA drugs is more complex. There are 6 underlying groups in our analysis that demonstrate that subgroups exist beyond simply “adherent” and “not-adherent.” The intermediate groups represent patients who fluctuate between adherence and non-adherence over time. This work extends the methods for evaluating the heterogeneity of oral 5-ASA medication adherence among patients with UC. Further research is needed to understand which factors may be useful for guiding interventions that target enhancements for adherence in this population.