Abstract
IMPORTANCE: For people with type 2 diabetes (T2D), out-of-pocket medication costs may influence medication choice, adherence, and overall diabetes management and progression. Little is known about how these costs change as insured people enter Medicare at age 65 years, when coinsurance in the coverage gap and catastrophic phases of Part D coverage can be increased greatly by use of insulin and newer, branded medications (eg, dipeptidyl peptidase 4 inhibitors, glucagon-like peptide 1 agonists, and sodium-glucose cotransporter 2 inhibitors). OBJECTIVE: To identify whether reaching age 65 years is associated with T2D medication out-of-pocket costs and utilization. DESIGN, SETTING, AND PARTICIPANTS: This retrospective cohort study (2012-2020) featuring 7 years of follow-up used prescription drug claims data from the TriNetX Diamond Network. Participants included people in the US with diagnosed T2D, and claims for T2D medications were observed both before and after age 65 years. Data analysis was performed from October 2022 to September 2023. EXPOSURE: Reaching age 65 years, according to participants' year of birth. MAIN OUTCOMES AND MEASURES: The primary outcome was patient out-of-pocket costs for T2D drugs per quarter (inflation adjusted to 2020 dollars). Utilization, measured as binary utilization of specific classes, and the number of claims for mutually exclusive classes and combinations of classes were also examined. All outcomes were examined using regression discontinuity design. RESULTS: In claims data for 129 997 individuals with T2D diagnosed at ages 58 to 72 years (mean [SD] age, 65.50 [2.95] years; 801 235 female [50.9%]), reaching age 65 years was associated with an increase of $23.04 (95% CI, $19.86-$26.22) in mean quarterly out-of-pocket costs for T2D drugs, and an increase of $56.36 (95% CI, $51.48-$61.23) at the 95th percentile of spending, after utilization adjustment. Utilization decreased by 5.3% at age 65 years, from 3.40 claims per quarter (95% CI, 3.38-3.42 claims per quarter) to 3.22 claims per quarter (95% CI, 3.21-3.24 claims per quarter), but a shift in composition of utilization, including increased insulin use, was associated with additional increases in patient costs. CONCLUSIONS AND RELEVANCE: In this cohort study of individuals with T2D, the increase in spending upon reaching age 65 years (when most people enroll in Medicare) was associated with patient coinsurance in the coverage gap and catastrophic coverage phases of Medicare Part D. The increased patient cost burden at age 65 years and a modest reduction in overall T2D drug utilization suggest that as people with T2D age into Medicare, there is potentially an increase in nonadherence and diabetes complications.