[Behavior of serum 25-hydroxycholecalciferol in humans after administration of vitamin D and 25-OHD3].

Serum levels of 25 hydroxycholecalciferol were evaluated following i.m. and p.o. vit. D2 and D3 and p.o. 25OHD3 administration. While no increment in 25OHD3 serum levels were observed after i. m. administration of non-hydroxylated calciferols, a marked increment of the metabolite was found following the oral administration. However the peak values were largely impredictable. Acute and chronic p.o. administration of 25OHD3 determines a rapid and dose-dependent increase of the serum levels of the metabolite. In addition considering that a lower dosage is required of 25OHD3 compared to vit. D, this metabolite is preferable in the therapeutic use.