Cyanide Toxicity: How It Kills and Why Immunity Is Impossible
Cyanide blocks cytochrome c oxidase, preventing cells from using oxygen. Rhodanese detoxifies small amounts but capacity can't increase through exposure — making cyanide immunity impossible, unlike snake venom tolerance.
Cyanide kills by binding to cytochrome c oxidase in mitochondria, blocking the final step of cellular respiration. Cells cannot use oxygen to produce ATP (energy), causing rapid cellular death even when blood oxygen levels are normal. Key facts: - Lethal dose: approximately 1-3 mg/kg body weight for hydrogen cyanide - Mechanism: irreversible binding to the iron center of cytochrome c oxidase - Speed: death can occur within minutes at lethal doses Natural detoxification: - The enzyme rhodanese converts cyanide to thiocyanate (much less toxic), excreted in urine - This handles the small amounts of cyanogenic compounds found naturally in foods (almonds, cassava, stone fruit pits, lima beans) - The detoxification capacity is limited — exceeding it overwhelms the system Why mithridatism (building tolerance through repeated exposure) doesn't work: - Unlike some toxins where the body develops faster metabolic pathways, cyanide's mechanism of action doesn't allow adaptation - Rhodanese capacity cannot be meaningfully increased through exposure - Each exposure causes cellular damage that accumulates rather than builds resistance - This contrasts with snake venom (where antibody-mediated tolerance is possible) or alcohol (where liver enzyme upregulation provides some tolerance)