Adherence to antihypertensive medications in Omani patients: a comparison of drug biochemical analysis and the Morisky Medication Adherence Scale

BACKGROUND: Medication nonadherence is a major risk factor for suboptimal or failed hypertension pharmacologic therapy. OBJECTIVE: To determine the nonadherence rate to antihypertensive medications using high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) and the self-reported Morisky Medication Adherence Scale (MMAS). METHODS: This study used a prospective cross-sectional cohort design. Patients with hypertension aged ≥18 years and prescribed at least one antihypertensive medication were recruited from an outpatient hypertensive clinic at a tertiary healthcare institution in Oman. Adherence was assessed using LC-MS/MS urine analysis and the MMAS. RESULTS: In total, 162 patients completed the MMAS questionnaire and provided urine samples for LC-MS/MS analysis. The overall mean age of the cohort was 55 ± 13 years, and 57% of the patients were men. The mean systolic and diastolic blood pressures were 146 ± 18 mmHg and 79 ± 10 mmHg, respectively. Using the MMAS method, 65% of the patients reported nonadherence. However, LC-MS/MS analysis revealed that only 27% of the patients were nonadherent. The adherent group by LC-MS/MS had significantly lower systolic ( P = 0.026) and diastolic blood pressures ( P < 0.001) than the nonadherent group, whereas no differences were observed using the MMAS method. There was weak or no agreement between the MMAS and LC-MS/MS results ( P = 0.142). CONCLUSION: Almost one-fourth of our patients with hypertension were nonadherent to their medications. There was a weak concordance between the MMAS and LC-MS/MS methods in detecting medication nonadherence. Further research into noninvasive convenient adherence scales or methods and their correlations with LC-MS/MS analysis is warranted.