Studies on hydroxocobalamin. I. Excretion and retention of massive doses in control subjects.

Abstract A comparison has been made of the urinary excretion of cyanocobalamin and hydroxocobalamin. Massive doses were injected subcutaneously in eighteen control subjects without signs of abnormal vitamin B 12 metabolism. Distinctly more hydroxocobalamin was retained. The cyanocobalamin and the hydroxocobalamin labeled with Co 60 and Co 57 , respectively, were injected separately or simultaneously. In the latter study differential radioactive assay of the two isotopes was employed. When 500 μg doses were given separately 79 to 89 per cent of cyanocobalamin was excreted compared to 43 to 57 per cent of hydroxocobalamin. After injection of 1,000 μg 80 to 89 per cent of cyanocobalamin was excreted compared to 54 to 63 per cent of hydroxocobalamin. Sixty-four to 82 per cent cyanocobalamin and 31 to 37 per cent hydroxocobalamin were excreted after a simultaneous dose of 500 μg of each substance. There was a slower rate of disappearance from the injection site of the hydroxocobalamim than of the cyanocobalamin. In two of three patients followed with surface counting over the liver relatively more hydroxocobalamin radioactivity was found. It is concluded that the significantly greater retention of hydroxocobalamin than cyanocobalamin warrents further studies on the use of hydroxocobalamin for maintenance treatment in pernicious anemia.