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Organophosphate pesticide poisoning
Organophosphates inhibit acetylcholinesterase, so acetylcholine accumulates and over-stimulates muscarinic and nicotinic receptors; the life-saving treatment is atropine in escalating doses until the lung secretions dry, together with decontamination, respiratory support and consideration of an oxime.
Why it matters in the exam
The classic question describes a farmer or a patient who swallowed a pesticide, with small pupils, salivation, sweating, vomiting, diarrhoea, wheeze with copious bronchial secretions and bradycardia, sometimes with muscle fasciculations and weakness. The correct step is early IV atropine, and the marker of adequate treatment is "dry" lungs — not the size of the pupils.
Treatment details are also tested: atropine 1–2 mg in an adult, doubling the dose every 5 minutes until the secretions dry, the heart rate is above 80 and the systolic pressure above 80; an oxime (pralidoxime) early, before "ageing" of the bond between the compound and the enzyme; and benzodiazepines for seizures. Staff protect themselves with gloves and gowns, and the patient's clothes are removed and the skin washed.
Know the late complications too: the "intermediate syndrome" usually appears one to four days after the poisoning, with proximal muscle weakness, weak neck flexors, cranial nerve palsies and respiratory failure — even after the cholinergic signs have resolved. A delayed neuropathy can appear after weeks. Carbamates cause a similar but shorter picture because their bond to the enzyme is reversible. Suxamethonium is forbidden for intubation in this poisoning because of prolonged paralysis.
Key points
- Acetylcholinesterase inhibition: muscarinic, nicotinic and central signs.
- The main danger — bronchial secretions, bronchospasm and respiratory failure.
- Atropine 1–2 mg, doubling every 5 minutes until the lungs are dry.
- Early oxime; benzodiazepines for seizures; no suxamethonium.
- Intermediate syndrome after 1–4 days — respiratory monitoring.
Summary table
| Effect group | Signs | Meaning | Treatment |
|---|---|---|---|
| Muscarinic | Salivation, lacrimation, sweating, diarrhoea, vomiting, bronchial secretions, bronchospasm, bradycardia, small pupils | The main danger — drowning in secretions | Atropine until the lungs are dry |
| Nicotinic | Fasciculations, weakness, paralysis, tachycardia, hypertension | Respiratory muscle failure | Oxime, ventilation |
| Central | Confusion, seizures, coma | Brain injury | Benzodiazepines, support |
| Late | Neck and proximal weakness after 1–4 days | Intermediate syndrome | Respiratory monitoring, ventilation |
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Sources
- Eddleston M et al., Management of acute organophosphorus pesticide poisoning (The Lancet), 2008 — Clinical management
- Goldfrank's Toxicologic Emergencies, 11th edition (2019) — Insecticides: organic phosphorus compounds and carbamates
- Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 9th edition (2020) — Pesticides
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.