Medication Adherence in the Real World: Lessons from the Diuretic Comparison Project

Background/Objectives: Antihypertensive treatment is crucial for preventing major adverse cardiovascular events, but suboptimal adherence remains a challenge. Methods: This is a secondary analysis of routine care data from a large pragmatic trial comparing two thiazide diuretics: chlorthalidone (CTD) and hydrochlorothiazide (HCTZ). In the trial, 13,523 older hypertensive patients were randomized from 72 Veterans Affairs medical centers. Medication possession ratio (MPR), reflecting adherence to either study medication (CTD or HCTZ), was used and compared across all randomized patients. Results: The overall median MPR was 95% for all randomized patients and 80% for 6656 individuals who reached 2.4 years for the average follow-up. Lower MPR was observed in Black, separated, urban-living, and comorbid patients. About 30% of the participants (n = 4022) were categorized as non-adherent using a definition of MPR < 80%. Those with baseline systolic blood pressure ≥ 136, recent smoking history, and prior heart failure and Black participants had decreased odds of having an MPR ≥ 80%, while increased odds of reaching that threshold were observed in those who had an eGFR ≥ 60, received ≥3 antihypertensive medications, were married, or resided in rural areas. Conclusions: This analysis provided assessment of real-world medication adherence in a sizable older hypertensive cohort. The proportion of non-adherence found in our analysis was comparable to national trends for US older adults taking blood pressure medications. Identifying sociodemographic characteristics and health conditions associated with non-adherence can help clinicians design targeted interventions for improved adherence to clinically prescribed medications. This is important as hypertension and the older adult population are both expected to grow significantly in the future.