Interactions between 1,25‐dihydroxyvitamin D 3 and vitamin D 2 : Effects of pharmacologic doses in normal individuals

To determine whether the administration of 1,25‐dihydroxyvitamin D 3 (1,25(OH) 2 D 3 ) affects the conversion of a pharmacologic dose of vitamin D 2 to 25‐hydroxyvitamin D (25OHD), 20 normal subjects received two separate doses of vitamin D 2 —one with and the other without the concomitant administration of 1,25(OH) 2 D 3 . Serum 1,25(OH) 2 D rose in response to 1,25(OH) 2 D 3 administration and fell when vitamin D 2 was given alone. Serum osteocalcin rose in response to 1,25(OH) 2 D 3 administration. Serum 25OHD rose in response to vitamin D 2 administration regardless of whether the subjects also received 1,25(OH) 2 D 3 . The data from this study in humans support the suggestion that the effects of 1,25(OH) 2 D 3 on serum 25OHD concentrations are mediated through mechanisms other than impairment of production. Clinical Pharmacology and Therapeutics (1987) 42 , 641–645; doi: 10.1038/clpt.1987.212