The role of medication adherence as a determinant of blood pressure control in a managed care population

Background: Disease management initiatives to improve hypertension care, commonly conducted in managed care organizations today, focus on many determinants of blood pressure control including medication adherence. Empirical evidence supporting the association between adherence and improved control is lacking. This study was designed to evaluate the relationship between medication adherence and blood pressure control in a cohort of hypertensive managed care enrollees. Methods: Prescription claims data for hypertensive adults continuously enrolled in a managed care plan throughout the calendar year 2000 were evaluated. A medication possession ratio (MPR, a measure of medication adherence) was calculated for each member, and patients with at least 50% adherence were eligible for the study. Medical records were then reviewed for a randomly selected cohort of those eligible members, stratified by calculated MPR. The association between degree of adherence and hypertension control was assessed. Results: Blood pressure was controlled in 48.3% of enrolled patients (n = 708). There was no significant association between MPR and overall blood pressure control noted (prevalence ratio = 1.11; 95% CI 0.94, 1.31); however, adherence was associated with an increased likelihood of controlled diastolic blood pressure (prevalence ratio = 1.15; 95% CI 1.05, 1.27). Conclusions: Hypertension is influenced by a variety of complex physiologic and behavior factors. When evaluated in isolation, overall blood pressure control does not appear to be independently associated with adherence. Interventions affecting multiple determinants of hypertension control should be given priority over those only designed to increase medication adherence when efforts to improve hypertension management are considered.