Decreased antihyperglycemic drug use driven by high out-of-pocket costs despite Medicare coverage gap closure

Objectives: Using the 2016 Medicare part D coverage gap as an example, we explored effects of increased out-of-pocket costs on adherence to branded dipeptidyl peptidase-4 inhibitors (DPP-4i) in patients without financial subsidies, relative to subsidized patients who do not experience increased spending during the gap. We also explored seasonality of re-initiation, as discontinuers may be more likely to reinitiate in January when benefits reset.

Methods: DPP-4i or sulfonylureas initiators, aged >66 years, from a 20% sample of 2015-2016 Medicare claims were identified. We used difference-in-differences Poisson regression to compare adherence before and after entering the coverage gap between non-subsidized and subsidized patients. Among discontinuers, monthly hazard ratios (HRs) for re-initiation relative to January 2016 were derived with Cox models. As a second control, we repeated analyses using sulfonylureas, generic low-cost alternatives.

Results: In 2016, 8,096 subsidized and 6,173 non-subsidized DPP-4i initiators entered the coverage gap. Non-subsidized patients, copayment in the coverage gap was 45% ($227 per DPP-4i prescription), and adherence decreased from 68.4% to 49.0% after gap entry. Accounting for adherence differences in subsidized patients, non-subsidized patients demonstrated reduced adherence to DPP-4is [Difference-in-difference:-16.9%;CI(-18.7%,-15.1%)] but not sulfonylureas [-1.6%(-3.4%,0.2%)]. Re-initiation was lowest in the months before January (HR=0.4-0.5) among non-subsidized DPP-4i patients, demonstrating a strong seasonal pattern.

Conclusions: Increased out-of-pocket costs negatively affect adherence and re-initiation of branded antihyperglycemic drugs among patients without financial subsidies. Despite closure of the coverage gap, affordability remains a concern given increasing list prices for many drugs on Medicare and the growing use of deductibles and coinsurance by commercial health plans.