Population Pharmacokinetic Analysis of the Cathepsin K Inhibitor Odanacatib: Insights Into Intrinsic and Extrinsic Factor Effects on Exposure in Postmenopausal and Elderly Women.

Abstract

This analysis developed a population pharmacokinetic (PK) model for odanacatib, characterized demographic and concomitant medication covariates effect, and provided odanacatib exposure estimates for subjects in phase2/3 studies. Data from multiple phase1 (P005, P025, and P014), phase2b (P004 and P022), and phase3 (Long-Term Odanacatib Fracture Trial; P018) studies were pooled to create a data set of 1280 postmenopausal women aged 45 to 91 years (102 from phase1, 514 from phase2b, and 664 from phase3) who received weekly oral odanacatib doses ranging from 3 to 100mg. A 1-compartment model with first-order absorption, dose-dependent relative bioavailability (F1), and first-order elimination best described odanacatib PK. F1 decreased from the 100% reference bioavailability for a 3-mg oral dose to 24.5% for a 100-mg dose. Eight statistically significant covariates were included in the final PK model: body weight, age, race, and concomitant cytochrome P450 (CYP)3A inhibitors on apparent clearance; body weight on apparent central volume of distribution; and concomitant hydrochlorothiazide, high-fat breakfast, and a study effect on F1. All fixed- and random-effects parameters were estimated with good precision (%standard error of the mean ≤29.5%). This population PK analysis provides insights into intrinsic- and extrinsic-factor effects on odanacatib exposure in postmenopausal and elderly women with osteoporosis. The magnitude of the intrinsic-factor effects was generally modest (odanacatib exposure geometric mean ratios, 0.80-1.21) even in subjects aged >80 years, or in subsets with multiple combinations of factors.