Comparison of Morisky Medication Adherence Scale with therapeutic drug monitoring in apparent treatment-resistant hypertension

The Morisky Medication Adherence Scale (MMAS-8) is a questionnaire developed for screening of non-adherence in patients with several chronic conditions, including uncomplicated hypertension. However, its accuracy in predicting non-adherence in patients with apparent treatment-resistant hypertension (a-TRH) is not known. Accordingly, we performed a retrospective study in 47 patients with a-TRH who had completed the eight-item MMAS during the initial clinic visit. Non-adherence was defined as presence of undetected serum levels of at least one prescribed antihypertensive drug by therapeutic drug monitoring. We found that 26% of patients were considered to have low adherence score (<6), while the actual prevalence of non-adherence was 51% by therapeutic drug monitoring. Sensitivity of the MMAS-8 was 26% (95% confidence interval, 10.3%-48.4%) with specificity of 75% (95% confidence interval, 53.3%-90.2%). By multivariate analysis, the MMAS-8 score was not an independent predictor of non-adherence, while certain clinical parameters such as heart rate were found to be independent predictors of non-adherence. Our study suggested limited accuracy of the MMAS-8 in detecting medication non-adherence in a-TRH.