Pharmacokinetics and bioequivalence of generic and branded abiraterone acetate tablet: a single-dose, open-label, and replicate designed study in healthy Chinese male volunteers.

PURPOSE: Abiraterone acetate is a highly variable drug and has been approved for the treatment of patients with metastatic castration-resistant prostate cancer in many countries. This study was conducted to compare the pharmacokinetic profile between the test product (abiraterone acetate tablet) and reference product ZYTIGA® (250 mg) mainly. METHODS: To overcome the high intra-subject variability of abiraterone, a two-sequence and four-period crossover study was designed to assess bioequivalence between the two products in 32 healthy male Chinese subjects under fasting conditions. The plasma concentration of abiraterone was analyzed by a validated liquid chromatography tandem mass spectrometry (LC-MS/MS) assay and the reference-scaled procedure was used to determine bioequivalence for the pharmacokinetics parameters. RESULTS: The point estimate of geometric mean ratios with 90% confidence interval (CI) of maximum observed concentration (Cmax) and the area under the concentration-time curve (AUC0t) for abiraterone in the test and reference products were 100.19% (90% CI 87.05-115.32%) and 105.99% (90% CI 96.34-116.62%), respectively, and were both within the range of 80.00-125.00%. The 95% confidence upper limit bound for [Formula: see text] was - 0.1079 for Cmax and was - 0.0515 for AUC0t. CONCLUSIONS: Bioequivalence was demonstrated between the two abiraterone acetate products. The study also confirmed high intra-subject variability, for abiraterone: coefficient of variation (CV, %) of Cmax values for the test and reference products were 40.33% and 46.58%, while for AUC0t were 24.02% and 34.16%, respectively. TRIAL REGISTRATION: http://www.chinadrugtrials.org.cn/ : CTR20170997.

The Effect of Food on the Intraluminal Behavior of Abiraterone Acetate in Man.

To relate the reported positive effect of food on the oral bioavailability of abiraterone to the intraluminal behavior of abiraterone acetate, an in vivo experiment was performed, in which duodenal fluids and plasma samples were collected from healthy volunteers after the administration of abiraterone acetate in fasted and postprandial conditions. The plasma concentration-time profiles confirmed the positive food effect. Nevertheless, intraduodenal concentrations of abiraterone acetate and abiraterone did not fully reflect this observation. This apparent discrepancy was explored by performing several in vitro experiments including solubility, dissolution, and transfer studies. Gastrointestinal transfer studies illustrated a positive impact of gastric processing of the abiraterone acetate formulation on the duodenal concentrations in the fasted state, which could not be observed in the postprandial condition. As the influence of gastric dissolution on the intraluminal concentrations in the small intestine declines aborally, it is most likely the superior solubility of abiraterone acetate and abiraterone in intestinal fluids of the fed state that dictates the food effect. Furthermore, N-oxide abiraterone sulfate and abiraterone sulfate appeared in the duodenum at significantly later time points than abiraterone, suggesting biliary excretion of these abiraterone metabolites; this was confirmed by in situ biliary excretion experiments in rats.