Validation of a self-administered instrument to measure adherence to anticholinergic drugs in women with overactive bladder

Abstract

Aim: To validate a self-administered instrument, the Medication Adherence Self-Report Inventory (MASRI) for measuring adherence to anti-cholinergic medication for overactive bladder (OAB). Methods: Prospective study in 131 women with OAB treated with fesoterodine. Adherence was measured at 8 and 12 weeks using an interviewer administered brief medication questionnaire (BMQ) that assesses barriers to adherence (criterion standard), the MASRI, and pill count. Construct, concurrent and discriminant validity of the MASRI was assessed. We hypothesized that women who were non-adherent as measured by the MASRI would be more likely to have a belief barrier than women who were adherent to medication. Results: Women diagnosed as non-adherent by the MASRI were more likely to report a belief barrier to taking medication as compared to adherent women at 8 weeks (80% vs. 38%, P < 0.001) and at 12 weeks (70% vs. 40%, P = 0.003). Significant correlations were noted between adherence rates measured by the MASRI and the BMQ at 8 weeks (r = 0.87, P < 0.001) and 12 weeks (r = 0.90, P < 0.001). Moderate correlation was noted between the adherence rate as measured by the MASRI and pill count at 8 weeks (r = 0.49, P = 0.02) but not at 12 weeks (r = 0.05, P = 0.87). The MASRI correctly identified 93% and 96% of non-adherent women at 8 and 12 weeks, respectively. Sensitivity, specificity, and positive likelihood ratio of the MASRI for predicting non-adherence was 91%, 82%, and 5.1 at 8 weeks and 90%, 85% and 6.1 at 12 weeks. Conclusions: The MASRI is a valid self-administered tool for measuring adherence to anticholinergic medication in women with OAB.