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

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Health Services Research

Published online on


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.