Blood cyanide levels in mice after administration of amygdalin

Oral doses of amygdalin and intraperitoneal (i.p.) doses of potassium cyanide (KCN) in the near-lethal range were administered to CD2F1 female mice. Blood cyanide levels were then measured as a function of time. The maximum cyanide level after amygdalin administration was reached at about 11/2 to 2 h and was within the range of values seen after KCN administration. Behaviour of mice correlated with the time of maximum blood cyanide level. Acute distress was observed at times when the cyanide level was highest. There was great variability in the nature and magnitude of the response in individual mice. The ability of the contents of various regions of the gastrointestinal tract and of tumour tissue to release cyanide from amygdalin was assessed. Stomach and upper intestine had little activity while the lower end and the faeces released large amounts. Again, there was a large variation between mice. These results are interpreted to mean that enteric contents are primarily responsible for the release of cyanide from ingested amygdalin. Freshly minced tumour tissue released negligible amounts of cyanide. Ten-fold higher doses of amygdalin administered i.p. produced very small increases in blood cyanide levels and no toxic behaviour. The doses used are comparable to doses which might be ingested by patients receiving oral amygdalin or Laetrile and indicate that oral amygdalin is potentially extremely dangerous.