Simultaneous measurement of apalutamide and N-desmethylapalutamide in human plasma using high-performance liquid chromatography with ultraviolet detection.

Background: The combination of apalutamide, a nonsteroidal androgen receptor inhibitor, with androgen deprivation therapy enhances survival in patients with metastatic castration-sensitive prostate cancer. However, apalutamide exhibits complex pharmacokinetics and dose-dependent adverse effects, necessitating dose adjustments to optimize its therapeutic outcomes. To facilitate effective monitoring, a high-performance liquid chromatography (HPLC) system coupled with an ultraviolet (UV) detector was developed for quantifying plasma concentrations of apalutamide and its active metabolite, N-desmethylapalutamide.

Main body: This method employed an ODS18 column (100 mm × 2.1 mm) with UV detection at 254 nm. The mobile phase comprised 20 mM acetate buffer (pH 5.0) and acetonitrile in a 60:40 ratio, and the run time was 10 min. The precision and accuracy were validated according to guidelines issued by the Food and Drug Administration (FDA). Long-term stabilities of the analytes were confirmed at both - 20 and - 80 °C over periods of 2 and 4 weeks. Peaks for enzalutamide (internal standard), N-desmethylapalutamide, and apalutamide were detected at 4.4, 5.8, and 7.7 min, respectively. Calibration curves demonstrated linearity within a concentration range of 0.5-20 µg/mL for both analytes in human plasma (R² = 0.9999). Additionally, the intraday and interday variability and stability remained within FDA guidelines.

Short conclusion: This work therefore presents a robust and simple HPLC-UV method for the simultaneous quantification of apalutamide and N-desmethylapalutamide in clinical therapeutic drug monitoring.