Anticipated Impact of Generic Imatinib Market Entry on the Costs of Tyrosine Kinase Inhibitors.

backgroundImatinib was the first BCR-ABL tyrosine kinase inhibitor (TKI) approved in the United States for the treatment of patients with chronic myelogenous leukemia and is currently the most prescribed TKI. The impending loss of patent exclusivity for imatinib has the potential to reduce costs for payers.

objectiveThe primary objectives of this study were to estimate the economic impact of the loss of patent exclusivity for branded imatinib and to calculate the relative impact of requiring prior authorization (PA) for the use of generic imatinib before a branded TKI. The secondary objective was to evaluate the potential relative cost impact of using a preferred branded TKI in addition to the PA requirement for generic imatinib before a branded TKI.

methodsA Microsoft Excel-based model was developed from the perspective of a US payer (commercial and Medicare) for a 2-year period. Data on utilization, patient out-of-pocket cost, and market share were obtained from an analysis of Truven Health MarketScan claims. It was assumed that the cost of generic imatinib would be 47.8% of the price of branded imatinib. It was assumed that 70% of patients receiving branded imatinib would shift to generic imatinib in year 1, and 95% would shift in year 2 after loss of patent exclusivity. Formulary management could be applied through PA requiring the use of generic imatinib before a branded TKI for patients newly prescribed TKI therapy. It was assumed that 74% of PA requests would be approved, and that the administrative cost of each would be $20.

resultsIn a hypothetical 1 million member commercial plan, the loss of patent exclusivity for branded imatinib produced cost-savings of $6.8 million during 2 years, or 28.8% of the total pharmacy spending on the TKI class. The savings were even greater in a 1 million member Medicare plan, at $22.9 million (28.8%). Formulary management reduced incremental TKI spending by 1.1% and 2.2% for the commercial and Medicare plans, respectively.

conclusionsIn the absence of formulary management beyond generic substitution, the loss of patent exclusivity for branded imatinib is expected to reduce total pharmacy spending on TKIs by nearly 33% during 2 years. Given the small number of newly treated patients, formulary management of the TKI class through restricted access to branded imatinib, with or without a preferred branded TKI, has limited potential for incremental cost-savings.