Population Pharmacokinetics of 25-Hydroxy Vitamin D in Non-Elderly Postmenopausal Women

Abstract

Vitamin D is one of the keys to bone health, and the serum levels of this vitamin are a major concern for postmenopausal women. The aims of this study were to develop a population pharmacokinetic (PPK) model for the clearance of 25-hydroxy vitamin D in non-elderly postmenopausal women and to identify the factors which have a significant influence on its clearance. The study population consisted of postmenopausal women who had been referred for evaluation of bone mineral density (BMD) by DEXA (dual-energy x-ray absorptiometry) scanner. The population pharmacokinetics modeling was conducted using the ADVAN 1 subroutine from a non-linear mixed effects (NONMEM) program, and thirty-two covariates were assessed. A total of 75 serum concentrations were obtained from the same number of postmenopausal women and used for PPK analysis. The mean value of the participantsí age was 57.92 ± 3.93 years and their body weight was 69.76 ± 11.49 kg. A wide range of 25-hydroxy vitamin D concentrations was observed (from 3.41 to 61.92 ng/mL) with a mean value of 26.19 ± 10.95 ng/mL. A total of 32 covariates were examined and preliminary results suggested the influence of six covariates on 25-hydroxy vitamin D clearance. In the final PPK model, however, only one covariate was shown to have a significant impact on the clearance value ñ the mean daily dietary intake dose of vitamin D (DD). These findings offer a preliminary basis on which to determine the level of vitamin D supplementation required by individual postmenopausal women. It could prove particularly important in achieving optimal serum levels of vitamin D in this vulnerable population.