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

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posted on 08.07.2020 by Mugdha Gokhale, Stacie B. Dusetzina, Virginia Pate, Danielle S Chun, John B. Buse, Til Stürmer, Emily Gower
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.

Funding

This work was supported by the following - The Medicare database infrastructure used for this was funded by the Pharmacoepidemiology Gillings Innovation Lab (PEGIL) for the Population-Based Evaluation of Drug Benefits and Harms in Older US Adults (GIL200811.0010), the Center for Pharmacoepidemiology, Department of Epidemiology, UNC’s Clinical Translational Science Award (UL1TR002489), the Cecil G. Sheps Center for Health Services Research, and the School of Medicine. The development of the state-of-the art nonexperimental methodology was supported by an ongoing grant from the National Institute on Aging (R01 AG056479).

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