Medication acquisition and self-reported adherence in veterans with hypertension

Abstract

Objectives: To examine factors associated with oversupply and undersupply of antihypertensive medication, and examine evidence for medication acquisition as distinct from self-reported adherence.

Research design: Analysis of pharmacy refill records, medical charts, and in-person interviews.

Subjects: Five hundred sixty-two male veterans with hypertension enrolled in a randomized controlled trial to improve BP control.

Measures: Patients were classified as having undersupply (<0.80), appropriate supply (> or = 0.80 and < or = 1.20), or oversupply (>1.20) of antihypertensive medication in the 90 days before trial enrollment based on the ReComp algorithm. Determination of BP control was based on clinic measurements at enrollment. Demographic, clinical, psychosocial, and behavioral factors relevant to medication-taking behavior and BP were assessed at enrollment.

Results: Twenty-three percent of the patients had undersupply, 47% had appropriate supply, and 30% had oversupply of antihypertensive medication. Multinomial logistic regression revealed that using fewer classes of antihypertensive medications and greater perceived adherence barriers were independently associated with greater likelihood of undersupply. Current employment was associated with decreased likelihood of oversupply, and greater comorbidity and being married were associated with increased likelihood of oversupply. Agreement between ReComp and self-reported adherence was poor (kappa = 0.19, P < 0.001). Undersupply, oversupply, and self-reported nonadherence were all independently associated with decreased likelihood of BP control after adjusting for each other and patient factors.

Conclusions: Antihypertensive oversupply was common and may arise from different circumstances than undersupply. Measures of medication acquisition and self-reported adherence appear to provide distinct, complementary information about patients' medication-taking behavior.