Abstract
Mecobalamin (CH_3-B_<12>), 500μg, was administered to 12 healthy adult volunteers by intravenous (IV) and intramuscular (IM)) injection by the cross-over method, and then the change in total B_<12> concentration in the serum was compared. The maximum serum B_<12> concentration (ΔC_<max>) and the area under the time curve (ΔAUC) of the serum total B_<12> concentration were both higher following IV injection than after IM injection: ca. 3.8-fold and 1.8-fold, respectively. These differences between the two administration routes were statistically significant. However, the saturated-bound rate, which reflects the amount of transcobalamin-II, was 90% or higher during the 1-12 hour period after administration by both routes. The subsequent pattern of decrease in this rate was similar for both routes. In addition, CH_3-B_<12> was administered to 6 healthy adult volunteers by IV injection of 500μg once a day for 10days. The minimum serum total B_<12> concentration (ΔC_<min>) increased gradually during the administration period and was about 1.7 times higher on 3 days after administration than on the first day. There-after, the concentration became constant. Moreover, the total B_<12> urinary excretion and the saturated-bound rate were increased during the 24-48 hour period after completion of the repeated administration. These findings indicate that, in repeated administration, B_<12> is accumulated in the liver and then gradually released into the blood.
