Conversion of Cyanocobalamin to a Physiologically Occurring Form

Abstract

Results are presented which indicate that in guinea pigs cyanocobalamin undergoes conversion to hydroxocobalamin, in vivo and in vitro, at the approximate rate of 0.1-0.4 mµg./day/Gm. of liver. In boiled liver, no conversion was found. The radioactivity excreted in human urine the first 12 hours after a therapeutic cyanocobalamin dose, on the other, is still cyanocobalamin. It is suggested that demonstrated metabolic differences between therapeutically used cyanocobalamin and hydroxocobalamin are explained, in part, by the time needed to convert cyanocobalamin to hydroxocobalamin.

Body Distribution, Turnover Rate, and Radiation Dose after the Parenteral Administration of Radiovitamin B121

“…1) In all calculations the assumption had to be made that the isotope is uniformly distributed within the tissues studied. The uneven intracellular distribution (5, 34,38,51,54) of radioactivity may well give more radiation to some cellular structures and less to others. However, this factor could not be considered in the present calculations.…”