Pharmacokinetics of oral calcitriol in healthy human based on the analysis with an enzyme immunoassay

We investigated the pharmacokinetics of 2 μg calcitriol in eight healthy human after a single oral administration. Plasma calcitriol was analyzed by sensitive and quantitative enzyme immunoassay following intra- and inter-day validation. In subjects, AUC0–∞ and AUC0–24 h were 267 and 246 pg h ml−1, respectively. Although the mean plasma concentration of calcitriol in human subjects did not return to baseline at 24 h post-dosing, the mean ratio of AUC0–24 h to AUC0–∞ was greater than 80%. The Cmax of calcitriol was measured at 3.4 h after administration as 50.0 pg ml−1. From our results, it can offer new opportunities to design and determine individually appropriate therapeutic dosage regimens based on a pharmacokinetic profile and be used for bioequivalence and revaluation study of generic drug.