Background: Effective treatment for chronic diseases often requires medication refill persistence. Health plans have frequently increased the amount of member cost-sharing by implementing tier-copayment pharmacy benefit designs and raising copayments. However, increased member costshare may present a barrier to the management of chronic conditions. Little is known about the relationship between the magnitude of member cost-sharing and antihypertensive persistence among members newly initiating therapy.
Objective: To investigate and quantify the relationship between amount of prescription cost-sharing and medication refill persistence among members newly initiating therapy with a single-agent angiotensin system blocker--either an angiotensin-converting enzyme inhibitor (ACEI) or angiotensin II receptor blocker (ARB).
Methods: This was an observational cohort study of pharmacy and medical claims data for 29 employers with approximately 310,000 beneficiaries that did not have a change in pharmacy benefits including the amount of member cost-share in 2004. The claims data were supplemented with census data for household income and race at the Zip Code level. Selected patients were new users of single-agent ACEIs or ARBs (i.e., excluding ACEI or ARB in combination with hydrochlorothiazide or amlopdipine) between January 1 and June 30, 2004, without a pharmacy claim for an ACEI or an ARB in the 6 months prior to the index claim for either drug type. Medication refill persistence was measured in 3 ways: (1) total number of days without ACEIs or ARBs during 6 months follow-up, (2) proportion of days covered (PDC) with less than 80% defined as nonpersistent during 6 months follow-up, and (3) number of days to the first gap of more than 30 days in medication coverage from the index date to end of 2004 (mean [SD] follow-up=9.2 [1.8] months). Three statistical models were fit: Tobit model, examining the association between cost-sharing and total number of medication gap days; logistic regression, testing the association between cost-sharing and odds of being nonpersistent; and Cox proportional hazards model, assessing the association between cost-sharing and time to a 30-day gap.
Results: Among the eligible population, a study cohort of 1,351 members newly initiating a single-agent ACEI or ARB was identified. These members were 41.8% female and had a mean age of 55.9 (SD=13.1) years. On average, their member cost-share was $12.42 (SD=$8.50) per 30-day supply. Each $1 increment in per 30-day cost-share was associated with a 1.9% increase in total gap (beta=0.019, 95% confidence interval [CI], 0.007-0.030, P=0.001), a 2.8% increase in the odds of being nonpersistent (odds ratio [OR]=1.028, 95% CI,1.011-1.045, P=0.001), and a 1.0% increase in the risk of having a gap of more than 30 days (hazard ratio [HR]=1.010, 95% CI, 1.001-1.019, P=0.034). Following transformation of the cost-sharing coefficient in each model, a $10 increment in cost-share had a consistent negative influence; 18.9% greater total gap days (beta=0.189, 95% CI, 0.073-0.304), 31.9% greater odds of being nonpersistent (OR=1.319, 95% CI, 1.120-1.553), and 10.2% larger hazard of having a gap of more than 30 days (HR=1.102, 95% CI, 1.007-1.205).
Conclusion: For members newly initiating single-agent angiotensin system blocking medication, the amount of prescription cost-sharing was associated with a negative impact on refill persistence.