Impact of Cost-Sharing Increases on Continuity of Specialty Drug Use: A Quasi-Experimental Study

Pengxiang Li, Tianyan Hu, Xinyan Yu, Salim Chahin, Nabila Dahodwala, Marissa Blum, Amy R. Pettit, Jalpa A. Doshi

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


Objective: To examine the impact of cost-sharing increases on continuity of specialty drug use in Medicare beneficiaries with multiple sclerosis (MS) or rheumatoid arthritis (RA). Data Sources/Study Setting: Five percent Medicare claims data (2007–2010). Study Design: Quasi-experimental study examining changes in specialty drug use among a group of Medicare Part D beneficiaries without low-income subsidies (non-LIS) as they transitioned from a 5 percent cost-sharing preperiod to a ≥25 percent cost-sharing postperiod, as compared to changes among a disease-matched contemporaneous control group of patients eligible for full low-income subsidies (LIS), who faced minor cost sharing (≤$6.30 copayment) in both the pre- and postperiods. Data Collection/Extraction Methods: Key variables were extracted from Medicare data. Principal Findings: Relative to the LIS group, the non-LIS group had a greater increase in incidence of 30-day continuous gaps in any Part D treatment from the lower cost-sharing period to the higher cost-sharing period (MS, absolute increase = 10.1 percent, OR = 1.61, 95% CI 1.19–2.17; RA, absolute increase = 21.9 percent, OR = 2.75, 95% CI 2.15–3.51). The increase in Part D treatment gaps was not offset by increased Part B specialty drug use. Conclusions: Cost-sharing increases due to specialty tier-level cost sharing were associated with interruptions in MS and RA specialty drug treatments.

Original languageEnglish
Pages (from-to)2735-2757
Number of pages23
JournalHealth services research
StatePublished - Aug 2018


  • Medicare
  • chronic illness
  • observational data/quasi-experiments
  • pharmaceuticals: prescribing/use/costs


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