Cyanide Poisoning

Outline

Bitter almond and cherry leave extracts known to cause death for centuries
Egyptian capital punishment "penalty of peach"
Hundreds died in 1978 in Jones town British Guiana following mass suicide using cyanide.

Wide variety of species, most common in prunus species; apricot, peach, plum, apple, pear, crab apple, almond, cherry. Hydrangea and cassava
Cyanide found in young leaves, seeds and kernels.
Warming or crushing of seeds gives " bitter almond" odour ? due to hydrocyanic acid. Less than 50% of people have ability to detect the odour.. Ability to detect is X-linked recessive trait, M:F 3:1 inability to detect.
Cases of reported toxicity
- 40 apricot kernels as milkshake
- 12 bitter almonds
- 1 wild apricot seed in a child
- Boiled hydrangea leaves as a "tea"

Potent cellular toxin
Inhibits cellular respiration by binding to ferric ion of cytochrome oxidase system and inhibits final step of oxidative phosphorylation
Cessation aerobic metabolism and development of cellular hypoxia, lactic acidosis and eventually cell death.
Detoxification mediated by hepatic mitochondrial enzyme Rhodanase by producing thiocyanate from thiosulphate.

Fe-cytochrome + cyanide -> CN-Fe-cytochrome

CN-Fe cytochrome + thiosulphate --*--> thiocyanate (* = rhodanase)

Inhalation of hydrogen cyanide gas – immediate effect
Ingestion of cyanide – symptomatic within minutes
Ingestion of plants and seeds - toxic component is amygdalin, requires hydrolysis by enzyme emulsin in the GIT to form cyanide hence may take hours for symptoms to develop.

Chelates cyanide directly to form cobalt cyanide
Small Vd-only binds to circulating cyanide
T1/2 – 1 hour
Dose - 300mg in 20mls dextrose over 1-5 min.
Repeat dose in 5 min. if necessary
Adverse effects – severe hypotension, cardiac dysrhythmias, convulsion and gross oedema.

Production of methaemoglobinaemia
Aim for level of 25-30% MetHb
MetHb has ferric ion available for binding cyanide
Clinical improvement in 5 minutes but MetHb takes 30 minutes to form
- Amyl nitrite perles – produces 5% MetHb
- Na nitrite – 300mg over 3 minutes produces 15-20% MetHb
- Na thiosulphate – 12.5g over 10 min provides substrate for detoxification
Adverse effects – production of up to 30% MtHb is well tolerated except in concurrent carbon-monoxide poisoning. Na thiosulphate is safe but can not use as first line antidote because of slow onset of action.

Cyanide poisoning from smoke inhalation
Self-poisoning with clinical signs and associated lactic acidosis
When there is suspicion that cyanide poisoning is the cause in unknown coma or cardiovascular instability

CH 14th Nov, 2001