The management of patients with acute poisoning has become increasingly important in recent years. Acute poisoning is common in suicide cases, in children and due to consumption of illicit liquor and to a lesser extent due to accidental overdose of a drug. Nonspecific measures such as maintenance of vital functions and removal and elimination of poisons and specific measures as apply to individual drugs form the treatment of poisoning.
Nonspecific Measures for the Treatment of Poisoning:
Depression of respiration in unconscious patients is a common cause of death in poisoning. Respiratory stimulants do not help and are potentially dangerous. Unobstructed airway, assisted ventilation and oxygen therapy (high concentration, particularly in carbon monoxide and irritant gases poisoning) are the mainstay for maintenance of ventilation. Many CNS depressants cause circulatory failure. A systolic blood pressure of less than 70 mm Hg may cause irreversible damage to the vital organs such as brain and kidney. Treatment should consist of oxygen therapy and IV fluids. Vasopressor drugs are contraindicated.
Removal and Elimination of the Poison:
Removal of poison from the gut by gastric lavage is not necessary, if the risk of toxicity is small or if the poison has been taken for more than 1 hour. Gastric lavage is contraindicated in corrosive poisoning, poisoning due to petroleum products and in comatose patients, unless a cuffed endotracheal tube protects the danger of inhalation of stomach contents.
Emetics have a very limited role, though ipecacuanha has been used for induction of emesis in conscious patients, when the poison ingested is neither corrosive nor a petroleum distillate, and when gastric lavage is inadvisable or refused or when the poison is not adsorbed by activated charcoal. Salt solutions, copper sulphate, apomorphine and mustard are dangerous and should not be used as emetics.
In general, gastric lavage or emetics do not empty the stomach completely and because of the danger of inhalation of stomach contents, emetics are best avoided in the treatment of poisoning. Prevention of the absorption by giving activated charcoal (50 g) through a nasogastric tube is relatively safe and more effective even though the poison was taken earlier than 1 hour.
Specific Drugs for the Treatment of Poisoning:
Poisoning can occur with any drug when taken in excessive (toxic) doses. Some of the common drugs, symptoms of poisoning and their antidotes are given in Table 20.1.
Chelating Agents for the Treatment of Poisoning:
These substances render an ion (generally a metal) biologically inactive by incorporating it into inner ring structure of the molecule. They are used in the treatment of cyanide and heavy metal poisoning. Dicobalt edetate chelates cyanide ion in the blood. Cyanide causes cellular anoxia by chelating the metallic (Fe+++) part of the intracellular respiratory enzyme, cytochrome P 450 oxidase.
Specific therapy consist of dicobalt edetate which is to be used only when patient is tending to loose, or has lost consciousness. Side effects of dicobalt edetate include vomiting, chest pain and anaphylactic shock. If dicobalt edetate is not available or is ineffective, sodium nitrite followed by sodium thiosulphate is given to convert the cyanide released from methemoglobin to the inactive thiocyanate. Oxygen at high pressure (hyperbaric) is given to overcome cellular anoxia.
Dimercaprol (BAL) contains SH groups which combine with heavy metals and thus spares SH groups of the body. It is used in poisoning by heavy metals antimony, arsenic, bismuth, gold, mercury and possibly thallium. It is also used an adjunct to sodium calcium edetate in lead poisoning. BAL is contraindicated in iron, cadmium or selenium poisoning and hepatic impairment.
Penicillamine chelates toxic metals particularly copper and lead. It is a metabolite of penicillin that contains SH groups so that it is similar to dimercaprol in action. It is used in Wilson’s disease, which is due to excessive deposition of copper in the brain and liver. It was also used in rheumatoid arthritis.
Sodium calcium edetate (EDTA) is the chelating agent that combines more avidly with lead than with calcium. Adverse effects with EDTA are fairly common and include lachrymation, nasal stuffiness, chills, myalgia, hypotension and renal damage. Desferrioxamine is the iron chelating agent used in iron poisoning which may occur as a result of repeated blood transfusion or accidental poisoning in children. Adverse effects are common and include GIT disturbances, arrhythmias, anaphylaxis and convulsions.