Cherry laurel (Prunus laurocerasus) and many other Prunus species, including peaches, cherries, apricots, plums and nectarines contain cyanogenic glycosides. These compounds are hydrolysed by an enzyme to produce hydrogen cyanide (HCN, hydrocyanic or prussic acid). In intact plant material the cyanogenic glycosides are separated from the enzyme, and it is only when they come into contact as a result of grinding, chewing, crushing, wilting, freezing or digestion of the plant that hydrolysis occurs.
The risk of cyanide poisoning in cats and dogs is small from ingestion of these plants; ruminants in contrast are much more efficient at breaking down plant material and numerous cases of cyanogenic glycoside poisoning are reported.
Most dogs and cats that ingest plants containing cyanogenic glycoside develop gastrointestinal signs with vomiting, diarrhoea and abdominal discomfort. There may also be constipation and there is risk of gastrointestinal obstruction depending on the quantity and size of the fruit eaten. Management is supportive.
Signs of cyanide poisoning are uncommon in cats and dogs. These signs include dilated pupils, hyperventilation, dyspnoea, weakness, tremors, hypotension and collapse. In severe cases there may be coma, convulsions, lactic acidosis, cardiac arrhythmias and pulmonary oedema.
You may see on the Internet that vitamin B12 is the antidote to cyanide, however, hydroxocobalamin is vitamin B12a, the precursor to cobalamin (vitamin B12). It acts by binding to cyanide to form cyanocobalamin which is excreted in the urine. Vitamin preparations containing vitamin B12 or vitamin B12a are of too low a dose to be practical in the management of cyanide poisoning. A specific high-dose hydroxocobalamin cyanide antidote product is available for use in humans with cyanide poisoning (usually from smoke inhalation) but it is very expensive and not readily available.