Differences in cardiovascular disease risk when antihypertensive medication adherence is assessed by pharmacy fill versus self-report: the Cohort Study of Medication Adherence among Older Adults (CoSMO)

Abstract

Background: Pharmacy refill adherence assesses the medication-filling behaviors, whereas self-report adherence assesses the medication-taking behaviors. We contrasted the association of pharmacy refill and self-reported antihypertensive medication adherence with blood pressure (BP) control and cardiovascular disease (CVD) incidence.

Methods and results: Adults (n = 2075) from the prospective Cohort Study of Medication Adherence among Older Adults recruited between August 2006 and September 2007 were included. Antihypertensive medication adherence was determined using a pharmacy refill measure, medication possession ratio (MPR; low, medium, and high MPR: <0.5, 0.5 to <0.8, and ≥0.8, respectively) and a self-reported measure, eight-item Morisky Medication Adherence Scale (MMAS-8; low, medium, and high MMAS-8: <6, 6 to <8, and 8, respectively). Incident CVD events (stroke, myocardial infarction, congestive heart failure, or CVD death) through February 2011 were identified and adjudicated. The prevalence of low, medium, and high adherence was 4.5, 23.7, and 71.8% for MPR and 14.0, 34.3, and 51.8% for MMAS-8, respectively. During a median of 3.8 years' follow-up, 240 (11.5%) people had a CVD event. Low MPR and low MMAS-8 were associated with uncontrolled BP at baseline and during follow up. After multivariable adjustment and compared to those with high MPR, the hazard ratios for CVD associated with medium and low MPR were 1.17 [95% confidence interval (CI) 0.87-1.56)] and 1.87 (95% CI: 1.06-3.30), respectively. Compared to those with high MMAS-8, the hazard ratios (95% CI) for MMAS-8 for medium and low MMAS-8 were 1.04 (0.79-1.38) and 0.89 (0.58-1.35), respectively.

Conclusion: While both adherence measures were associated with BP control, pharmacy refill but not self-report antihypertensive medication adherence was associated with incident CVD. The differences in these associations may be because of the distinctions in what each adherence measure assesses.

Figure 1. Recruitment and Follow up Flowchart for the Cohort Study of Medication Adherence among Older Adults (CoSMO)

Adapted from Krousel-Wood et al. Med Clin N Am 93:753–769, 2009 *Ineligible during the recruitment phase due to no confirmed diagnosis of hypertension (22.9%), hard of hearing (16.4%), too ill to complete survey (12.6%), deceased (11.5%), cognitive screen failure (11.1%), not currently prescribed antihypertensive medication (8.4%), no longer enrolled in managed care organization (6.9%), non-English speaker (5.8%), confined to a nursing home (1.9%), moved out of state (1.1%), current treatment for cancer (1%), or miscellaneous reason (<1%). ^ Ineligible in the follow up phase due to hospitalization for CVD outcome in the year prior to the baseline survey †Reason for exclusion: missing Medication Possession Ratio (MPR) data in the year prior to the baseline survey CVD-cardiovascular disease

Figure 2. Cumulative incidence of Cardiovascular Disease Outcome by Level of Antihypertensive Medication Adherence at Baseline

Figure 2a: Medication Possession Ratio (MPR) Figure 2b: Morisky Medication Adherence Scale (MMAS-8) *P-value for Log-Rank test CVD-Cardiovascular Disease MPR—Medication Possession Ratio MMAS-8—Morisky Medication Adherence Scale 8-item Composite CVD outcome-myocardial infarction, congestive heart failure, stroke, or cardiovascular death