The Association between Type of Insurance Plan, Out-of-Pocket Cost, and Adherence to Antihypertensive Medications in Medicare Supplement Insurance Enrollees.

Abstract

Medicare supplement insurance, or Medigap, covers 21% of Medicare beneficiaries. Despite offsetting some out-of-pocket (OOP) expenses, remaining OOP costs may pose a barrier to medication adherence. This study aims to evaluate how OOP costs and insurance plan types influence medication adherence among beneficiaries covered by Medicare Supplement plans. We conducted a retrospective analysis of the MerativeTM MarketScan® Medicare Supplement Database (2017-2019) in Medigap enrollees (≥ 65 years) with hypertension. Proportion of days covered (PDC) was a continuous measure of medication adherence and was also dichotomized (PDC ≥ 0.8) to quantify adequate adherence. Beta-binomial and logistic regression models were used to estimate associations between these outcomes and insurance plan type and log-transformed OOP costs, adjusting for patient characteristics. Among 27,407 patients with hypertension, the average PDC was 0.68 ± 0.31; 47.5% achieved adequate adherence. A mean $1 higher in 30-day OOP costs was associated with a 0.06 (95% Confidence intervals [CI]: -0.09 - -0.03) lower probability of adequate adherence, or a 5% (95% C.I.: 4% - 7%) decrease in PDC. Compared to comprehensive plan enrollees, the odds of adequate adherence were lower among those with point-of-service plans (O.R.: 0.69, 95%C.I.: 0.62 - 0.77), but higher among those with preferred provider organization (PPO) plans (O.R.: 1.08, 95%C.I.: 1.01 - 1.15). Moreover, the association between OOP costs and PDC was significantly greater for PPO enrollees. While Medicare supplement insurance alleviates some OOP costs, different insurance plans and remaining OOP costs influence medication adherence. Reducing patient cost-sharing may improve medication adherence.