Adherence to antihypertensive medication and its predictors among non-elderly adults in Japan

Nonadherence to antihypertensive drugs is a primary reason for suboptimal clinical outcomes among hypertensive patients. We assessed adherence to newly initiated antihypertensive medications in non-elderly Japanese patients and examined which patient and facility characteristics were associated with low adherence. We selected new oral antihypertensive drug users, aged 30–74 years, between 2014 and 2016 from a large administrative claims database. We measured adherence as the proportion of days covered (PDC) during a 1-year follow-up and divided patients into three groups of low (PDC < 40%), intermediate (PDC ≥ 40% to <80%), and high (PDC ≥ 80%) adherence. Factors associated with low adherence were assessed by logistic regression analysis with generalized estimating equations. Among 31,592 patients (mean age, 51.7 years; 41.2% female), the median 1-year PDC was 88.5% (IQR: 41.9–98.1%). In total, 59.2%, 16.6%, and 24.2% of patients were categorized as having high, intermediate, and low adherence, respectively. Female sex (odds ratio [OR] 1.15, 95% confidential interval [95% CI] 1.08–1.22), younger age, and the initiation of angiotensin-converting enzyme inhibitors (OR 1.37, 95% CI 1.12–1.66), beta-blockers and thiazide diuretics (OR 4.82, 95% CI 4.34–5.36 and OR 3.91, 95% CI 2.79–5.46, respectively; compared with angiotensin II receptor blockers) were associated with low adherence. Patients initiating antihypertensives at larger hospitals (≥200 beds) were more likely to be adherent. While adherence to antihypertensive drugs in non-elderly Japanese patients was relatively high compared with that reported in previous studies in Western countries, patients with intermediate-low adherence may benefit from targeted interventions.