Does Cyanocobalamin Contain Cyanide?
Yes, cyanocobalamin contains a cyanide molecule, but it is a stable, non-toxic form of vitamin B12 that is safely used as a nutritional supplement and is actually the product formed when hydroxocobalamin binds to and detoxifies free cyanide ions.
Chemical Structure and Formation
- Cyanocobalamin is the compound formed when hydroxocobalamin (a form of vitamin B12) binds with cyanide ions 1, 2
- The cyanide molecule is tightly bound to the cobalt center of the cobalamin structure, rendering it non-toxic and allowing safe renal excretion 1
- This binding mechanism is precisely why hydroxocobalamin works as a cyanide antidote—it scavenges free toxic cyanide and converts it into harmless cyanocobalamin 3, 1
Clinical Context: Antidote vs. Supplement
The cyanocobalamin formed during cyanide poisoning treatment is the therapeutic endpoint, not a source of toxicity:
- When hydroxocobalamin is administered for cyanide poisoning (5-10 grams IV for adults), it directly binds cyanide ions to form cyanocobalamin, which is then safely excreted by the kidneys 3, 1
- Studies demonstrate a linear relationship between initial blood cyanide concentration and plasma cyanocobalamin formation after hydroxocobalamin treatment, with 5 grams capable of binding all available cyanide up to blood concentrations of approximately 40 μmol/L 4
- The American Heart Association recommends hydroxocobalamin as first-line therapy for cyanide poisoning specifically because it neutralizes cyanide without compromising oxygen-carrying capacity, unlike alternative antidotes 3, 5
Safety Profile
- Cyanocobalamin as a vitamin B12 supplement contains only trace amounts of cyanide in a stable, bound form that poses no clinical toxicity 6
- The cyanide molecule in cyanocobalamin cannot dissociate to cause poisoning—it remains bound to the cobalamin structure 6
- Hydroxocobalamin has not been associated with clinically significant toxicity even in antidotal doses, and can be safely administered even to non-poisoned patients 5
Important Clinical Distinction
The key pitfall is confusing the stable cyanide-cobalamin bond in cyanocobalamin with free toxic cyanide:
- Free cyanide reversibly binds to mitochondrial cytochrome oxidase, halting cellular respiration and causing rapid toxicity within minutes 7, 1
- Cyanocobalamin's cyanide is irreversibly bound and metabolically inert, making it the desired end-product of cyanide detoxification 1, 2
- Cyanocobalamin cannot effectively remove additional cyanide due to poor binding capacity—only hydroxocobalamin serves as the active antidote 6