December 1, 2010

Copayment Level and Drug Switching: Findings for Type 2 Diabetes

Erin P. Saito, PhD; James W. Davis, PhD; Rosanne C. Harrigan, MS, EdD; Debora Juarez, ScD; and Marjorie K. Mau, MD

The American Journal of Pharmacy Benefits

Objective: To assess the relationship between copayment level and drug switching among insured patients who initiated a medication regime for treatment of type 2 diabetes.

Study Design: Retrospective observational study.

Methods: Medical claims data were used to examine continuous periods of use for therapeutic classes of drugs within formulary tiers. Switching to more expensive drugs or drugs of equal or lesser cost was based on the relevant out-of-pocket costs to the patient for the initial drug versus the drug the patient switched to. Data were analyzed using multistate proportional hazards models.

Results: A total of 9260 participants met the inclusion criterion. Each $5 increase in copayment was associated with decreased rates of switching to a relatively more expensive drug (hazard ratio [HR] = 0.49, 95% confidence interval [CI] = 0.43, 0.56) and an increased rate of switching to drugs of equal or lesser cost (HR = 1.04, 95% CI = 1.03, 1.05). Patients with better glycemic control were more likely to switch to relatively less expensive drugs in response to increased copayments (HR = 1.10, 95% CI = 1.07, 1.13). Compared with Japanese patients, Filipinos and Native Hawaiian or Pacific Islanders had the greatest difference in rates of drug switching at lower copayments, whereas Chinese patients had the greatest rates of switching at higher copayments.

Conclusions: Cost sharing can shift patients with diabetes toward use of less expensive drugs. Clinical and sociodemographic factors affect the rates of switching. Clinical implications of drug switches should be examined.

Download PDF

Publication Archive

Sort through our publications archive by year. A downloadable PDF is available for each publication.