Relationship of the magnitude of member cost-share and medication persistence with newly initiated renin angiotensin system blockers.

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.