Characterizing Pharmacokinetic Variability of Topiroxostat in Chinese Population: Insights from a Phase I Randomized Clinical Trial

Objective: This Phase I clinical trial aimed to address the knowledge gap regarding topiroxostat's use outside Japan by characterizing its pharmacokinetic profile, safety, and efficacy in healthy Chinese subjects. Methods: The trial followed a randomized, open-label, three-dose group design, enrolling 12 healthy participants and administering topiroxostat at three different dose levels. The study utilized NONMEM software for pharmacokinetic analysis, evaluating the impact of demographic and biochemical covariates on drug disposition. Results: Pharmacokinetic analysis shows the peak drug concentration (Cmax) under a single oral administration of 20, 40, and 80 mg of Topiroxostat, which was found in healthy subjects to be 215.46 ± 94.04 ng/mL, 473.74 ± 319.83 ng/mL and 1009.63 ± 585.98 ng/mL, respectively. The time to peak drug concentration (Tmax) was longer in females (0.79–0.98 h) than in males (0.53–0.93 h). Activated partial thromboplastin time (APTT) and triglycerides (TG) were included as covariates for the typical value of the absorption rate constant (TVKA) in our pharmacokinetic model. The dose (DOSE) was considered a covariate for the typical value of bioavailability (TVF1), and sex (SEX) was considered a covariate for the typical value of clearance (TVCL). The typical population values for topiroxostat included Q/F at 4.91 L/h, KA at 0.657 h-¹, Vc/F at 32.5 L, Vp/F at 30 L, and CL/F at 124 L/h. Conclusion: The trial successfully established the pharmacokinetic parameters of topiroxostat in a Chinese population, confirming its safety and efficacy. The results support the need for individualized dosing strategies and optimize therapeutic outcomes.