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

We investigated the pharmacokinetics of 2 microg 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, AUC(0-infinity) and AUC(0-24h) 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 24h post-dosing, the mean ratio of AUC(0-24h) to AUC(0-infinity) was greater than 80%. The C(max) of calcitriol was measured at 3.4h 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 reevaluation study of generic drug.