Association between prescription burden and medication adherence in patients initiating antihypertensive and lipid-lowering therapy

Purpose. The association between prescription burden and medication adherence in patients initiating antihypertensive and lipid-lowering therapy was studied. Methods. Patients enrolled in managed care organizations who initiated antihypertensive therapy coincident with lipid-lowering therapy (no more than 90 days apart) between January 1, 1997, and April 30, 2000, were eligible for inclusion. Analysis was limited to new users of antihypertensive and lipid-lowering therapy. The proportion of days covered (PDC) by anti hypertensive and lipid-lowering therapy was calculated for the first year after therapy initiation; patients with a PDC of >= 80% for both drug classes were considered adherent. Prescription burden was defined as the number of prescription medications taken in the year prior to starting anti hypertensive and lipid-lowering therapy. Demographic, clinical, and health-service-use variables associated with both prescription burden and medication adherence were measured using medical and pharmacy claims data from the year before initiation of antihypertensive and lipid-lowering therapy. Results. Among 5759 patients, the mean +/- S.D. prescription burden was 3.6 +/- 3.7 (median, 3) medications, and the mean +/- S.D. PDC with antihypertensive and lipid-lowering therapy was 53.9% +/- 31.9% (median, 58.5%). Among patients with 0, 1, and 2 prior medications, 41%, 35%, and 30% of patients were adherent, respectively, to antihypertensive and lipid-lowering therapy. Among patients with 10 or more prior medications, 20% were adherent. Conclusion. Among patients in a managed care database taking anti hypertensive and lipid-lowering medications, adherence to those regimens became less likely as the number of prescription medications increased. The reduction in adherence with additional prescription medications was greatest in patients with the fewest preexisting prescriptions.