Tuesday, January 15, 2019

Cyanide poisoning

Cyanide is a mitochondrial toxin that causes death within minutes to hours of exposure.

PATHOPHYSIOLOGY:
1)Cyanide avidly binds to the ferric ion (Fe3+) of complex IV thus inhibiting the Electron transport chain.
2)The cell must then switch to anaerobic metabolism of glucose to generate ATP.Anaerobic metabolism leads to the formation of lactic acid and the development of metabolic acidosis.

TREATMENT:

1)Sodium nitrite and Amyl nitrite induce formation of methemoglobin. Cyanide has high affinity to metHb. This provides an attractive alternative binding site for cyanide which makes the ETC free.
2)Sodium thiosulfate can be given which converts cyanomethemoglobin to thiocyanate and metHb. Thiocyanate is then renally excreted and metHb can be converted back to normal Hb by using methylene blue.
3) Hydroxocobalamin, a precursor of vitamin B12, avidly binds to intracellular cyanide (with greater affinity than cytochrome oxidase) forming cyanocobalamin. This molecule is stable and readily excreted in the urine.

-Srikar Sama

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