P428 New opportunities overcoming of the secondary inefficiencies of the anticytokine therapy in patients with inflammatory bowel disease

risk in a UK population, and to evaluate whether changes in 5-ASA formulation increase the risk of relapse. Methods: A retrospective cohort study was conducted using a UK pharmacy dispensing database. Adults who received continuous treatment with Asacol® (mesalazine) 400mg or 800mg oral tablets during a 6 month baseline period were followed for 18 months. Adherence was measured using the medication possession ratio (MPR); MPR 80 was classed as adherent. In this study, a doubling of MPR (peak MPR, indicating a doubling of 5-ASA dose) was used as a proxy for relapse. Switch was identified as a change to another oral 5-ASA. Relationships between adherence, switch and relapse were examined using cohort, nested case-control and subgroup analyses, controlled for age and gender. Results: 1,731 patient records were extracted, of which 568 patients received Asacol and had complete baseline and follow-up data (age, sex, interpretable MPR) for inclusion in the analysis (mean age 56 yrs, 51.2% male). There was a significant association between relapse and adherence during the follow-up period (RR 1.44, 95%CI 1.08 1.94; p = 0.014), indicating a relapse was more likely with lower adherence (mean MPR). In a subgroup of Asacol patients adherent in the baseline period (n = 276), switching medication was significantly associated with relapse in the follow-up period: 26.3% (62/236) who switched suffered relapses, compared to 7.5% (3/40) of those who did not switch (RR 3.5, 95%CI 1.16 10.62; p = 0.008). Conclusions: Non-adherence to mesalazine significantly increased the likelihood of relapse in this UK population. Moreover, in this study, adherent patients switched to another 5-ASA had a 3.5 times greater risk of relapse compared to nonswitched patients. This analysis represents the first evaluation of the impact of 5-ASA switch using a proxy for relapse in a nonclinical setting. These data may have substantial implications for disease management, but before making firm conclusions, further research is needed.