Impact of out-of-pocket pharmacy costs on branded medication adherence among patients with type 2 diabetes

Abstract

BACKGROUND: Medication adherence is pivotal for the successful treatment of diabetes. However, medication adherence remains a major concern, as nonadherence is associated with poor health outcomes. Studies have indicated that increasing patients' share of medication costs significantly reduces adherence. Little is known about a potential out-of-pocket (OOP) cost threshold where substantial reduction in adherence may occur. OBJECTIVE: To examine the impact of diabetes OOP pharmacy costs on antihyperglycemic medication adherence and identify the potential threshold at which significant reduction in adherence may occur among patients with type 2 diabetes mellitus (T2DM). METHODS: This was an observational, retrospective cohort study using longitudinal U.S. pharmacy and medical claims data from the IMS Health Medical Claims (Dx) database. Patients with T2DM who initiated therapy with a branded antihyperglycemic medication during the index period (January 1, 2011, to December 31, 2011) and had 3 years of follow-up data were included. The primary outcome was adherence to antihyperglycemic medications, measured as the number of days covered. Propensity scores were calculated using baseline sociodemographic and clinical characteristics to control for potential confounding factors. Four strata were created based on mean propensity scores. Across each stratum, patients were assigned to 5 diabetes OOP pharmacy (including generics) cost levels: $0-$10, $11-$40, $41-$50, $51-$75, and > $75. Multivariate regression models were used to estimate association of diabetes OOP pharmacy costs and adherence for each stratum. Sensitivity analyses were conducted to assess the impact of total OOP pharmacy costs and index drug category OOP costs on adherence. RESULTS: A total of 15,416 patients were assessed. Across each stratum in the diabetes OOP pharmacy cost analysis group, mean patient age ranged from 52.3 to 56.1 years, mean number of antihyperglycemic medication classes ranged from 1.5 to 3.2, and mean household income ranged from $60,763 to $79,373. Most patients used a commercial plan (55%-85%). The propensity-stratified multivariate regression model revealed an overall negative relationship between diabetes OOP pharmacy costs and adherence across several OOP cost levels. Diabetes OOP pharmacy cost level $51-$75 appeared as the threshold at which adherence reduced significantly (77-78 fewer days of coverage over 3 years of follow-up; P < 0.05) when compared with the lowest OOP costs ($0-$10) across all strata. Adherence reduced further (99-145 fewer days of coverage; P < 0.0001) for the higher diabetes OOP pharmacy cost levels ( > $75) when compared with the lowest OOP cost levels. Sensitivity analyses with total OOP pharmacy costs and index drug category OOP costs revealed negative association with adherence across all strata. CONCLUSIONS: Diabetes OOP pharmacy cost was negatively associated with patient adherence, and a potential OOP cost threshold ($51-$75) was identified at which adherence reduced significantly. The study findings may be beneficial in informing the design of health care plans to achieve optimal adherence and improve disease management in patients with T2DM.