5+ Year Member
Nov 26, 2013
Medical Student
FA says induced methemoglobinemia (using nitrites, followed by thiosulfate) may be used to treat cyanide poisoning. Can we quickly go over the mech here? Many thanks!


2+ Year Member
May 17, 2015
Medical Student
Nitrites (amyl or sodium ) cause oxidization of Fe2+ to Fe3+ (metHB) to release CN from ETC cytochrome Oxidase so we can make ATP. The MetHB binds well with CN (CN-metHB) and this displaces it from the Electron transport system.

Thiosulfate it donates its sulfur group to Liver Rhodanese(endogenous) this enzyme causes CN to thiocyanite(more water soluble for renal excretion )
Jun 30, 2015
Zurich, Switzerland
Just for a quick review:
  • Cyanide binds to Fe3+ → Blocks electron transport chain in mitochondria → Aerobic metabolism is stopped → Lactic acidosis (anion gap).
    Note that cyanide poisoning is not cyanotic.

There are 3 antidotes:

Nitrates: Creation of a controlled state of,methemoglobinemia, that will compete for cyanide.
  • Generate Fe3+ (methemoglobin) → binds cyanide (and gets it out from the mitochondria!)
Hydroxocobalamin (Cyanokit)
  • Precursor of VB12 binds cyanide → cyanocobalamin → excreted in urine
  • Cyanide is transformed to thiocyanate → excreted in urine

Combination and treatment choice is based on availability of drug and certainty of poisoning.
  1. Thiosulfate + Hydroxocobalamin
  2. Thiosulfate + Nitrates (if hydroxocobalamin is not available and strong suspicion of cyanide poisoning)
  3. Thiosulfate alone (if CI to nitrates, or not certain cyanide poisoning)