Feasibility and efficacy of therapeutic drug monitoring of abiraterone in metastatic castration resistant prostate cancer patients.

Background: Previous studies demonstrated better outcomes for mCRPC (metastatic castration resistant prostate cancer) patients with higher abiraterone exposure (minimal plasma concentration (C) > 8.4 ng/mL), but around 40% of patients experience exposure below this target. Pharmacokinetic (PK)-guided interventions following Therapeutic Drug Monitoring (TDM) could optimise exposure and outcomes. We aimed to evaluate the feasibility and effect on treatment outcomes of abiraterone TDM.

Methods: Patients with low exposure levels (Low-group, C < 8.4 ng/mL) got a PK-guided intervention. We compared exposure, adverse event (AE) incidence, time on treatment (ToT) and Prostate-Specific Antigen response rate (PSArr) between the Low-group and Adequate-group.

Results: We included 167 mCRPC patients, with 56 in the Adequate-group and 111 in the Low-group. Interventions were successful 86% of the time. Exposure between groups became corresponding (Low-group: 7.95 to 20.5 ng/mL, Adequate-group: 20.8 ng/mL, p = 0.72) with comparable AE incidence (17% vs. 23%, p = 0.4). Median ToT and PSArr were similar (351 vs. 379 days, p = 0.35; 61.3% vs. 67.9%, p = 0.51).

Conclusions: PK-guided interventions improved above target exposure from 33.5% to 81.4% of patients without additional AEs. While historically, low exposure patients had significantly shorter survival, PK-guided interventions eliminated this disparity. As interventions are effective, low-cost and safe, TDM for abiraterone should be considered to enhance treatment outcomes.