Which antidote for cyanide exposure also functions as a vitamin B12 derivative and forms cyanocobalamin?

• A. Hydroxocobalamin
• B. Pralidoxime
• C. Diazepam
• D. EDTA

Answer: (A)

Hydroxocobalamin is a vitamin B12–derived compound that directly tackles cyanide by binding it to form cyanocobalamin. When cyanide is present, it blocks mitochondrial respiration, leading to cellular hypoxia. Hydroxocobalamin has a high affinity for cyanide and sequesters it, producing cyanocobalamin, which is a non-toxic, excretable form of vitamin B12. This rapid binding lowers the cyanide concentration available to inhibit cytochrome c oxidase, quickly restoring cellular respiration. It’s favored for being fast-acting and not causing methemoglobinemia or other complications associated with some older antidotes. The other agents listed act through different mechanisms—pralidoxime reactivates acetylcholinesterase in organophosphate poisoning, diazepam provides sedation or seizure control, and EDTA chelates heavy metals—so they do not address cyanide poisoning or form cyanocobalamin.