Introduction:

Abiraterone was first approved by the US Food and Drug Administration in 2011 to treat metastatic castration-resistant prostate cancer. In 2018, a generic abiraterone formulation became available in the United States.

Since its approval, abiraterone has become one of the most prescribed medications for advanced prostate cancer, and is recommended for metastatic, locally advanced, and high risk localized disease across most clinical guidelines. However, prior studies have suggested considerable financial toxicity associated with advanced oral agents in prostate cancer, which may be mitigated by cheaper generic alternatives.

In this study, we aim to characterize the trend of Medicare Part D utilization and spending on branded versus generic abiraterone prescriptions from 2013 through 2023 and estimate the impact of generic abiraterone adoption on Medicare costs.

Methods:

Publicly available Medicare Part D data was analyzed from 2013-2023 for all 3 abiraterone formulations available in the United States (Zytiga, Yonsa, and generic abiraterone), extracting number of unique beneficiaries, 30-day fills, and total Medicare Part D spending annually. Total spending was divided by number of 30-day fills to estimate per-refill cost, and total spending was divided by number of beneficiaries to estimate average spending per beneficiary. Annual cost savings were estimated by multiplying the per-refill cost difference between branded and generic formulations by total 30-day fills for the generic formulation.

Annual percent change (APC) was analyzed using the Joinpoint Regression Program from the National Cancer Institute. Confidence intervals were determined using the empirical quantile method using a Monte Carlo resampling technique. P-values represent the likelihood that the slope of the fit line differs between joinpoints, or in the case of 0 joinpoints, that the slope differs from 0.

Results:

Medicare Part D spending on all abiraterone formulations increased from $470million to $1.5billion from 2013-2018 (APC 19.3%, 95% confidence interval [CI] 6.7% - 100.3%, p=0.02), decreasing to $910million in 2023 (APC -10.4%, 95% CI -45.8% - 0.4%, p=0.06). From 2013-2023, the number of beneficiaries per year increased from 14,188 to 46,411 (APC 12.3%, 95% CI 8.5% - 16.3%, p<0.01). From 2013-2017, the annual cost per beneficiary grew from $33,094 to $48,978 (APC 12.2%, 95% CI 1.6% - 37.1%, p=0.02), decreasing to $19,610 in 2023 (APC -17.7%, 95% CI -25.6% to -12.8%, p<0.01).

Medicare spending and number of beneficiaries for generic abiraterone increased after 2018, while those of Zytiga decreased. The per-refill cost of generic abiraterone decreased significantly after 2018 (APC -17.2%, 95% CI -27.7% to -5.5%, p=0.01). The cost difference between generic and branded abiraterone translates to Medicare savings of >$1billion per year in 2020-2023, with total savings of $7.3billion from 2018-2023.

Conclusion:

The introduction of a generic version of abiraterone has led to billions of dollars in Medicare cost savings. Generic abiraterone has largely supplanted its branded counterpart, with 98% of abiraterone prescriptions in 2023 being generic. Generic utilization was associated with dramatic reductions in both total Medicare Part D spending and per-beneficiary cost despite an increase in the number of beneficiaries receiving abiraterone. This highlights the potential impact of generic oral oncology drugs to expand access while also reducing cost.

Funding: N/A