What is the antidote/dose for cyanide poisoning?

• A. N-acetylcysteine
• B. Hydroxocobalamin 5 g IV/IO over 15 min
• C. Methylene blue
• D. Sodium nitrite

Answer: (B)

Cyanide poisoning blocks cells from using oxygen by inhibiting mitochondrial respiration. The antidote that works best in this situation is hydroxocobalamin, which binds cyanide to form cyanocobalamin (a non-toxic form of vitamin B12) that the body can excrete. The standard dose is 5 grams given IV or IO over about 15 minutes, and a second dose may be given if signs persist.

This option is preferred because it directly neutralizes cyanide without creating other problems with oxygen delivery. Other choices either treat different conditions (N-acetylcysteine for acetaminophen poisoning; methylene blue for methemoglobinemia) or use a strategy that can worsen oxygen delivery (sodium nitrite-induced methemoglobinemia to trap cyanide).