Toxicology · Short notes

Pesticide and Household Poisoning: Short Notes & Cheat Sheet

Organophosphates, aluminium phosphide, paraquat and rodenticides, plus kerosene, corrosives, carbon monoxide, methanol and snake bite.

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Short notes

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Common poisonings in Pakistan

Agricultural poisons dominate in rural areas; kerosene, corrosives and medicines dominate in children at home.

Pesticides

Organophosphates are the most common agricultural poisoning in Pakistan. They cause muscarinic effects (secretions, miosis, bradycardia), nicotinic effects (fasciculations, weakness) and CNS effects.
Treatment: remove clothing and wash the skin, give atropine and increase the dose until the chest is dry, give pralidoxime early, and use benzodiazepines for seizures.
An intermediate syndrome (proximal weakness and respiratory failure) can follow at 1–4 days, and a delayed neuropathy at 2–3 weeks.
Carbamates are reversible cholinesterase inhibitors with a shorter course.
Aluminium phosphide ('wheat pill') releases phosphine gas. It causes severe shock, arrhythmias and acidosis with a garlic or rotten-fish odour, has a high death rate and no specific antidote; treatment is supportive.
Paraquat is corrosive and causes progressive lung fibrosis. Avoid extra oxygen unless the patient is hypoxic.
Superwarfarin rat poisons (brodifacoum) cause bleeding for weeks and need prolonged high-dose vitamin K. Strychnine causes convulsions with a clear mind; treat with benzodiazepines.

Household poisons

Kerosene and other hydrocarbons: the danger is aspiration pneumonitis. Never induce vomiting or perform gastric lavage.
Corrosives (toilet acids, caustic soda): no vomiting, no neutralisation and no charcoal; arrange early endoscopy. Alkalis cause deeper (liquefactive) injury.
Carbon monoxide (heaters and gas geysers in winter) causes headache, confusion and coma. Give 100% oxygen: it shortens carboxyhaemoglobin half-life from about 4–6 hours on air to about 1 hour.
Methanol (adulterated liquor) causes blurred 'snowfield' vision and severe acidosis. Treat with fomepizole or ethanol, bicarbonate, folinic acid and haemodialysis.
Button batteries lodged in the oesophagus need urgent removal.

Bites and stings

Pakistan's important venomous snakes include cobra and common krait (neurotoxic) and Russell's viper and saw-scaled viper (haemotoxic).
Treatment: immobilise the limb, avoid tight tourniquets and cutting, and give polyvalent antivenom when there are signs of envenoming.
The 20-minute whole-blood clotting test detects the clotting defect of viper bites.
Severe scorpion stings with high blood pressure and cardiac effects are treated with prazosin.

Cheat sheet

High-yield facts in one place. Cover the right-hand column and test yourself.

Poison → key management

Poison	Management
Organophosphate	Decontaminate, atropine to dry chest, pralidoxime
Aluminium phosphide	Supportive; no antidote
Paraquat	Early charcoal/Fuller's earth; limit oxygen
Superwarfarin	High-dose vitamin K for weeks
Kerosene	No vomiting or lavage; watch lungs
Corrosives	No emesis, no neutralising; endoscopy
Carbon monoxide	100% oxygen; hyperbaric if severe
Methanol	Fomepizole/ethanol, bicarbonate, dialysis
Snake bite	Immobilise, polyvalent antivenom
Scorpion sting	Prazosin

Memory aids

Atropinise until the chest is dry: In organophosphate poisoning, titrate atropine to clear bronchial secretions, not to pupil size.

Exam traps

Pupil size is not the target for atropine dosing; dry lung secretions are.
Gastric lavage and induced vomiting are contraindicated in kerosene and corrosive ingestion.
Pulse oximetry can look normal in carbon monoxide poisoning.
High-flow oxygen can worsen paraquat lung injury.

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