OBJECTIVES:

There has been a surge in novel therapy (e.g., enzalutamide (ENZ)) of metastatic castration resistant prostate cancer (mCRPC) before and after docetaxel-based chemotherapy. ENZ, as a CYP3A4 inducer, has the potential to interact with other drugs. There is limited real-world data (RWD) to describe treatment patterns. Furthermore, there is a need to investigate enzalutamide drug interactions in different line of therapy among patients with mCRPC. Our study aimed to evaluate the treatment pattern by lines of therapy (LOT) in patients with mCRPC, and to describe the incidence and characteristics of co-prescribing ENZ and other medications with potential DDIs.

METHODS:

We established a cohort of older adults of initiating mCRPC treatment using SEER-Medicare 2012-2019. Patients were followed from the fill date of the 1st mCRPC prescription until death, disenrollment or the end of the study period. Treatment sequences and number of patients was assessed up to three LOTs at regimen levels. Potential ENZ-related DDIs were determined within each LOT, defined as >7 days of concomitant use with another medication. We evaluated DDIs duration in days, as well as prescriber and pharmacy characteristics.

RESULTS:

In total, 3,566 new users of mCRPC drugs were included (LOT1: 91.3%, LOT2:39.8%, LOT3: 16.6%). The mean age was 77 years and the median NCI comorbidity index was 0-1. The most commonly used agents were abiraterone, ENZ, and docetaxel in LOT1 to LOT3. Among 1,526 ENZ users, the most common DDIs were with warfarin (9.3%), apixaban (4.5%), and rivaroxaban (3.9%). Interacting drugs were written by different prescribers (72%-100%) and dispensed by different pharmacies (94%-100%) depending on interacting agent.

CONCLUSIONS:

Concurrent use between ENZ and anticoagulants was relatively common in clinical practice as indicated by RWD, leading to potential safety concerns.