How does hydroxocobalamin work as a cyanide antidote?
The hydroxyl ligand at the cobalt centre is readily displaced by cyanide, which has a very high affinity for cobalt, forming cyanocobalamin. That product is stable, non-toxic and simply excreted in urine. Administered intravenously at gram doses it therefore scavenges cyanide directly from the bloodstream rather than acting through an enzyme.
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Why is it preferred over older cyanide antidotes?
Because it is safe in patients who turn out not to be poisoned. Older antidotes work by inducing methaemoglobinaemia to bind cyanide, which is itself dangerous and is particularly hazardous in smoke inhalation victims who may already be hypoxic from carbon monoxide. Hydroxocobalamin can be given on suspicion without that risk.
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Why is hydroxocobalamin used for B12 injections?
Because it binds more strongly to plasma proteins than cyanocobalamin and is retained far longer in the body. That means injections can be given at much wider intervals, which is a substantial practical advantage in treating pernicious anaemia and malabsorption where lifelong parenteral supplementation is required.
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Is it available for oral use?
It is used in supplements, though the parenteral route is where its pharmacokinetic advantage is clearest. For oral supplementation the choice between B12 forms is driven more by stability, cost and marketing position than by a clear functional difference for most people. Light protection is required for all the non-cyano forms.
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