Labeled hydroxocobalamin, administered intramuscularly in man, is absorbed more slowly from the site of injection and deposited in the liver and calf muscle to a degree equal to or higher than that of cyanocobalamin at an equivalent dose. These findings, together with those reported in Part I of this paper, suggest the applicability of hydroxocobalamin as a long-acting vitamin B12 in man. These conclusions, however, require the support to be obtained from long-range observations on patients with vitamin B12 depletion.
Administration of 6 intramuscular injections of 1000 µg. hydroxocobalamin every other day for 10 days enabled 15 individuals with initial vitamin B12 serum levels of 81 to 242 (mean 185 ± 44 µµg./ ml.) to maintain vitamin B12 concentration of the blood 6 months later at levels exceeding 3 times the pretreatment values. In 12 of these individuals who were studied for at least a 10-month period, vitamin B12 concentration in the serum 10 months after conclusion of injections was still double the initial pretreatment levels. This difference was highly significant statistically (p = 0.001). Of 11 patients followed for 15 months after conclusion of injections, in 7 the serum levels were still higher than before treatment.
No comparable results were ever reported with cyanocobalamin therapy.
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