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.