High prevalence of potential drug-drug interactions in patients with castration-resistant prostate cancer treated with abiraterone acetate.

ABSTRACT

PURPOSE: Abiraterone acetate (AA), used to treat metastatic castration-resistant prostate cancer (mCRPC), inhibits androgen biosynthesis by blocking cytochrome P450 (CYP) 17A1. It also inhibits other cytochromes involved in the metabolism of various widely used medications. As such, there is presumably a high potential for drug-drug interactions (DDIs) that can diminish the efficacy of AA or concurrent medications, or increase the risk of DDI-related adverse events (AEs). However, the scale of AA-associated DDIs is currently unknown. METHODS: We conducted a retrospective review of pharmacy records and electronic patient charts to retrieve individual drug histories and on-treatment AEs of mCRPC patients beginning AA therapy in a tertiary care setting. Potential DDIs were analyzed using two commercial databases, Lexicomp and Micromedex. RESULTS: Eighty-four informative patients were identified. Sixty-five patients (77 %) and 44 patients (52 %) were flagged for one or more potential DDIs by the Lexicomp and Micromedex databases, respectively. One hundred eighty-four potential DDIs were identified overall, with a median of 1 DDI per patient in both databases. Possibly due to rigorous DDI screening before AA treatment initiation, we did not identify a definite instance of DDI-related AEs. CONCLUSIONS: The use of commercial DDI databases suggests a substantial risk of potentially consequential DDIs in mCRPC patients undergoing AA therapy. However, prospective investigations with larger patient populations are required to better establish the clinical relevance of these DDIs.