Pharmacokinetics of a single, large dose of cholecalciferol

Background: There is much interest in dosing vitamin D intermittently for patient convenience and long-term adherence. Objective: The objective was to characterize the time course and response of 25-hydroxyvitamin D (calcidiol) to a large oral dose of cholecalciferol. Design: One group (30 subjects) was supplemented with a single oral dose of 100 000 IU cholecalciferol. A second group (10 subjects) served as a control group to assess the seasonal change of calcidiol. Serum calcidiol concentrations were followed for 4 mo. The subjects were healthy with limited sun exposure (<10 h/wk) and milk consumption (<0.47 L daily). We excluded subjects with granulomatous conditions, liver disease, kidney disease, or diabetes and subjects taking anticonvulsants, barbiturates, or steroids. Results: Serum calcidiol rose promptly after cholecalciferol dosing from a mean (±SD) baseline of 27.1 ± 7.7 ng/mL to a concentration maximum of 42.0 ± 9.1 ng/mL. Seven percent of the supplemented cohort failed to achieve 32.1 ng/mL at any time point. The highest achieved concentration in any subject was 64.2 ng/mL. The control group had a nonsignificant change from baseline of -0.72 ± 0.80 ng/mL during 4 mo. Conclusions: Cholecalciferol (100 000 IU) is a safe, effective, and simple way to increase calcidiol concentrations. The dosing interval should be ≤2 mo to ensure continuous serum calcidiol concentrations above baseline. This trial was registered at www.clinicaltrials. gov as #NCT00473239.