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PHARMACOECONOMICS

The Impact of Methodological Approach on Cost Findings in Comparison of Epoetin Alfa with Darbepoetin Alfa

Lead Researcher, Thomson Reuters, Cambridge, MA

Stacey R Long, MS

Vice President, Thomson Reuters

William D Marder, PhD

Senior Vice President and General Manager, Thomson Reuters

Sean D Sullivan, PhD

Professor, Department of Pharmacy; Professor, Department of Health Services; Adjunct Professor, Department of Medicine, University of Washington, Seattle, WA

Joel Kallich, PhD

Director, Global Health Economics, Amgen, Thousand Oaks, CA

Reprints: Dr. Song, Thomson Reuters, 150 Cambridge Park Dr., 2nd Floor, Cambridge, MA 02140, fax 617/492-9365, xue.song{at}thomsonreuters.com

BACKGROUND: Two erythropoiesis-stimulating agents (ESAs), epoetin alfa and darbepoetin alfa, are approved for the treatment of chemotherapy-induced anemia in patients with cancer. Randomized controlled trials indicate that the drugs are similarly efficacious, but that the duration of clinical benefit (DCB) ranges from 2 to 7 days for epoetin alfa and from 7 to 21 days for darbepoetin alfa, depending on dose. Given equivalent efficacy, payers are increasingly interested in understanding the cost differences for these 2 drugs.

OBJECTIVE: To examine the impact of different methodological approaches on the cost comparison between epoetin alfa and darbepoetin alfa users, with cancer from a payer perspective.

METHODS: Episodes of care (episode) were constructed for cancer patients treated with ESAs, using MarketScan claims data. Episodes started with the first ESA claim and ended on the last ESA claim or the claim before a 42-day or longer gap in ESA therapy. Each episode was augmented with an estimated DCB based on the last dose in the episode. Cost was reimbursed amount observed in the claims database. Adjusted weekly cost was estimated using generalized linear models to control for difference in clinical and demographic differences across epoetin alfa and darbepoetin alfa episodes.

RESULTS: Episodes were created in 324 darbepoetin alfa and 342 epoetin alfa users. Darbepoetin alfa users tended to be younger, had more comorbidities, and had advanced cancer (all p < 0.001). After accounting for DCB, the average weekly cost of darbepoetin alfa was significantly lower than that of epoetin alfa ($619 vs $940; p < 0.001). After multivariate adjustment, darbepoetin alfa had lower costs than epoetin alfa in the base case and all alternative approaches.

CONCLUSIONS: To reduce the risk of potential bias, DCB and different patient characteristics should be taken into account when using retrospective claims data to conduct cost comparisons between agents that have significant differences in dosing schedule.

Key Words: erythropoiesis-stimulating agents, claims data, comparative study, cost analysis

Published Online, July 7, 2009. www.theannals.com, DOI 10.1345/aph.1L590