Background: Two oral agents for mCRPC patients who previously received docetaxel were recently approved by the US Food and Drug Administration—abiraterone acetate plus prednisone (AA+p) and enzulatamide (EN). Phase 3 studies in this population showed median treatment duration of 8 months for AA+p1 and 8.3 months for EN,2 while median survival was 15.81 months and 18.42 months, respectively. The budgetary impact of these products to payers depends, in part, upon real world treatment duration and the proportion of mCRPC patients utilizing each product.
Objective: To model the expected pharmacy costs of treatment with AA+p or EN in mCRPC patients previously treated with docetaxel.
Methods: Pharmacy costs of AA+p and EN were calculated by multiplying drug wholesale acquisition costs3 of a 30-day supply (AA 1,000 mg/d - $5,819.21, on 6/6/12; EN 1,000 mg/d - $7,450, on 8/31/12) by treatment duration (months) and number of post-docetaxel mCRPC patients receiving each therapy. The number of patients with prostate cancer at any stage was calculated by multiplying the age-adjusted rate of new prostate cancer cases (0.14%)4,5 by plan population size and proportion of males in the U.S. population (49.2%).6 Docetaxel-treated mCRPC population estimates were derived from a dynamic progression model.4 Two treatment durations, 8 months and 12 months, were modeled.
Results: In a 1,000,000 member plan, the model estimated 58 mCRPC patients with prior docetaxel chemotherapy. For an 8 month treatment duration, estimated cost of AA+p was $46,576 per patient and $59,600 per patient for EN, a difference of $13,024. Modeling 12 month treatment duration,the cost of AA+p was $69,864 per patient and $89,400 per patient for EN or a difference of $19,536 per patient. The expected budget impact of an 8 month treatment duration in a 1,000,000 member plan with 25% of post-docetaxel mCRPC patients receiving AA+p and 25% receiving EN was $674,781 (AA+p) or $863,473 (EN), a difference of $188,692. Based on similar assumptions, the expected budget impact of a 12 month treatment was $1,012,172 (AA+p) and $1,295,209 (EN), a difference of $283,037.
Conclusions: In this cost model for the treatment of post-docetaxel mCRPC patients, AA+p was less costly than EN when treatment duration was held constant. The higher modeled costs of EN therapy resulted in an additional $188,692 and $283,037 in plan spending for an 8 or 12 month course of therapy, respectively.
References: 1Zytiga® Prescribing Information; Janssen Biotech Inc. (12/2012). 2Xtandi® Prescribing Information; Astellas Pharma US, Inc. (12/2012). 3Analysource/First Data Bank. 4Solo K, et al. Presented at ASCO Annual Meeting, 2011. 5United States Census Bureau. http://www.census.gov/population/www/projections/usinterimproj/. Accessed on 09/07/12. 6United States Census Bureau. http://www.census.gov/prod/cen2010/briefs/c2010br-03.pdf. Accessed on 02/20/12.
