Assessing medication adherence in inflammatory bowel diseases. A comparison between a self-administered scale and a pharmacy refill index.

Background: Medication non-adherence in inflammatory bowel disease (IBD) has a negative impact on disease outcome. Different tools have been proposed to assess non-adherence. We aimed to compare a self-administered scale and a pharmacy refill index as a reliable measure of medication adherence and to determine what factors are related to adherence.

Methods: Consecutive non-active IBD outpatients were asked to fill in the self-reported Morisky Medication Adherence Scale (MMAS-8) and the Beliefs about Medication Questionnaire (BMQ). Pharmacy refill data were reviewed from the previous three or six months and the medication possession ratio (MPR) was calculated. Non-adherence was defined as MMAS-8 scores < 6 or MPR < 0.8.

Results: Two-hundred and three patients were enrolled (60% ulcerative colitis, 40% Crohn's disease); 51% were men, and the mean age was 46.3 (14) years. Seventy-four per cent of patients were on monotherapy and 26% on combination therapy; altogether, 65% received mesalazine, 46% thiopurines and 16% anti-tumor necrosis factor alfa. Non-adherence rate assessed by MPR was 37% and 22.4% by MMAS-8. Receiver operator curve analysis using a MMAS-8 cut-off of six gave an area under the curve of 0.6 (95% CI 0.5-0.7), p = 0.001. This score had an 85% sensitivity and 34% specificity to predict medication non-adherence, with negative and positive predictive values of 57% and 70% respectively. High scores in the BMQ potential for harm of medication were significantly associated with MPR non-adherence (p = 0.01).

Conclusion: The accuracy of MMAS-8 to identify medication non-adherence in inactive IBD outpatients in our setting is poor due to a low specificity and a negative predictive value. Psychosocial factors such as beliefs about medication seem to be related to IBD non-adherence.