Chemicals covered in this section
This section covers cyanide, hydrogen cyanide (also called hydrocyanic acid or prussic acid), sodium cyanide, and potassium cyanide.
Cyanide-releasing substances are found naturally in many plants, the stones of apricots and peaches, bitter almonds, cassava and tapioca. Cassava (also called manihot or manioc) is grown throughout the tropics and is a basic food in parts of Africa and South America. It is a bush or tree with green flowers and nuts. The root is solid and white. cyanide when they burn. When people are overcome by breathing smoke from fires, some of the effects may be due to cyanide poisoning.
Cyanide is used in industry and for pest control. Hydrogen cyanide is used to fumigate buildings, ships and aircraft infested with rodents or insects. Sodium cyanide and potassium cyanide are used in metal cleaning, ore extraction in mines, electroplating and the manufacture of synthetic fibres.
A preparation called Laetrile, made from peach stones, has been used to treat cancer, but there is no evidence that it does any good and it can cause cyanide poisoning.
How they cause harm
These chemicals stop living cells taking up oxygen and so the brain and heart are damaged by lack of oxygen. They are poisonous if swallowed, breathed in or spilt on the skin or in the eye. Chronic poisoning, from eating cassava as a major part of the diet, may damage the nervous system and thyroid gland.
How poisonous they are
These chemicals are highly poisonous and work very fast.
The toxicity of plants containing cyanide varies widely depending on where they grow and whether fertilizers are used. Some parts of the same plant may be more poisonous than others. All parts of the cassava plant are poisonous, but the leaves and skin of the root are the most poisonous parts. The poison is removed by washing and boiling.
It is important for people who use cyanide at work to use safe work practices to avoid being poisoned.
Cassava poisoning can happen if the root is not properly prepared and cooked. Mild cases of poisoning are common in poor areas, especially in undernourished children.
Signs and symptoms
* If swallowed, breathed in or spilt on the skin
Symptoms appear within seconds or minutes, but may be delayed by 1-2 hours if cyanide is swallowed with food.
- burning tongue and mouth (if cyanide is swallowed),
- throbbing headache,
- fast breathing,
These may be the only signs and symptoms in cases of mild poisoning.
In moderate poisoning:
- difficulty in breathing,
- chest pain,
- short periods of unconsciousness,
In severe poisoning:
- deep coma,
- slow pulse,
- low blood pressure,
- large pupils,
- breathing stops.
Death may occur within minutes. After a very large dose, the patient falls to the ground, wheezing, with violent fits and dies almost immediately.
* In the eyes:
- same effects as if swallowed, breathed in or spilt on the skin.
Weakness of the legs with pain or numbness, loss of sight, difficulty in coordination, swollen thyroid gland (in front of the neck).
What to do
Do not go into an area thought to be contaminated by cyanide gas unless you have breathing equipment approved for cyanide exposure, and protective clothing. Put on gloves and overalls before touching the patient.
Move the patient away from any poisonous gases into fresh air or away from spilt liquids or solids.
Give first aid. If the patient stops breathing open the airway, wash chemical off the patient's lips and mouth, then give mouth-to- mouth or mouth-to-nose respiration. Give heart massage if the heart stops. Keep on giving mouth-to-mouth respiration and heart massage for at least 30 minutes, even if the patient seems dead.
If the patient is unconscious or drowsy, lay him or her on one side in the recovery position. Check breathing and pulse every 3 minutes.
In the eye
Gently brush or dab away any liquid or powder from the face. Wash the eyes with water for at least 15-20 minutes. Check that there are no solid bits of chemical on the lashes and eyebrows, or in the folds of skin round the eyes.
On the skin
Immediately remove contaminated clothing, shoes, socks and jewellery, cutting them off if necessary. A delay of only seconds may make the poisoning worse. Wash the skin thoroughly with soap and water for 15 minutes, using running water if possible. If you have breathing equipment approved for cyanide exposure, wear this while you wash the patient, and wear protective clothing and rubber gloves so that none of the chemical gets on your own skin or clothes.
Take all patients with symptoms to hospital as quickly as possible.
What to do if there is a delay in getting to hospital
If the chemical was swallowed: if the patient is fully awake, breathing normally and has not had muscle twitching or fits, make the patient vomit.
Information for doctors outside hospital
* Severe poisoning
Continue cardiopulmonary resuscitation for at least 30 minutes or until the patient recovers.
General supportive care may be life-saving. Always give oxygen to patients with cyanide poisoning. If an antidote is not available, serious poisoning can sometimes be successfully treated with supportive care and oxygen alone.
Low blood pressure should be treated with intravenous fluids and dopamine.
Antidotes: There are four antidotes. They can be harmful if too much is given or if they are given to people who have not been poisoned with cyanide.
Give an antidote only if the patient is losing consciousness or is already deeply unconscious and you are sure of the diagnosis. Give 50 ml (12.5 g) of sodium thiosulfate 25% intravenously over 10 minutes. Then give one of the following:
1. Dicobalt edetate solution 1.5%: give 20 ml (300 mg) intravenously over one minute.
2. Sodium nitrite solution 3%: give 10 ml (300 mg) intravenously over 20 minutes.
3. 4-Dimethylaminophenol (4-DMAP) 5%: give 5 ml (250 mg) intravenously over one minute.
4. Hydroxocobalamin solution 40%: give 10 ml (4 g) intravenously over 20 minutes.
Some severely poisoned patients may fail to respond to the first dose of antidote. While repeat doses of hydroxocobalamin or sodium thiosulfate are unlikely to cause harm, any other specific antidote may itself be poisonous if too much is given or if it is given to someone who has not been poisoned with cyanide, if the patient does not respond, seek expert advice from a poisons centre before giving a repeat dose of any specific antidote other than sodium thiosulfate or hydroxocobalamin.
* Moderate poisoning
- Give 50 ml (12.5 g) of sodium thiosulfate 25%, intravenously over 10 minutes.
- Give 100% oxygen for 12-24 hours, but no longer.
* Mild poisoning
No antidote is needed. Give supportive care, including oxygen, and bed rest.
Chronic poisoning from cassava is not reversible. It may be due to poor preparation of the cassava or to too little protein in the diet. Education is necessary to prevent cases occurring