Management of Organophosphate Poisoning
Department of Internal Medicine PMHC
Introduction
Organophosphate pesticides are commonly used in South Africa, accidental or intentional exposure has a
mortality rate up to 25%. Organophosphates work by inhibiting acetylcholinesterse thereby leading to an
accumulation of acetylcholine and over stimulation of muscarinic and nicotinic receptors. Common
organophosphate pesticides include malathion, dichlorvos, trichlorfon, and fenitrothion/malathion.
Clinical Findings
Signs and symptoms can be divided into muscarinic, nicotinic and central nervous system effects.
Muscarinic effects (over stimulation acetylcholine receptors of the parasympathetic system.)
Bronchospasm, bronchorrhoea, salivation, urinatation, diarrhoea, miosis, hypotension, bradycardia and
vomiting.
Nicotinic effects (over stimulation acetylcholine receptors of the sympathetic system.)
Hypertension, mydriais, tachycardia and sweating.
Nicotinic effects at neuromuscular junction.
Confusion, agitation, coma, respiratory failure.
Central nervous system effects
Muscle weakness, fasciculations and paralysis (seizures may occur secondary to hypoxia or due to nerve
agents)
Investigation – Consider other substances may have also been ingested. Routine bloods, ECG and chest xray should be performed when patient has been stabilised.
Management
1. Ensure adequate airways protection –If the patient has respiratory distress intubate early (avoid
succinylcholine!)
2. Ensure adequate oxygenation – give high flow oxygen via a face mask.
3. Ensure adequate circulation – insert cannula and give ivi fluids
4. Give atropine until patient is fully atropinised. Start with 0.05mg/Kg of atropine ivi (2-4mg
depending on patient weight). Repeat every 15 mins until full atropinisation. Aim for pulse rate
>80 beats per minute and systolic blood pressure >80mm/Hg. Increase atropine bolus dose until
response occurs.
5. Start atropine infusion when atropinisation achieved – 0.05mg/kg/hour. E.g. for a 70kg patient
give 3.5 mg of atropine per hour as an infusion. Put 10mg of atropine in 200mLs of fluid run at 40
– 80mLs per hour (2-4mg/hr) depending on response.
6. Monitor patient ever 15 minutes. If the dose of atropine is too low cholinergic features will re
occur. If the dose of atropine is too high agitation, pyrexia, reduced bowel sounds and urinary
retention will occur – then reduce atropine infusion.
7. If patient presents within 24 hours of exposure and has signs of moderate to severe
organophosphate poisoning give obidoxime 250mg ivi – repeat after 2 hours. Note give obidoxime
after initial atropine bolus. Obidoxime is contraindicated in carbamate poisoning.
8. Perform a 12 lead ECG – treat arrhythmias as necessary, intravenous magnesium maybe helpful.
9. Monitor patient for secretions, pulse rate (use cardiac monitor), pupil size, blood pressure, oxygen
saturation and pulse. Ideally serial vital capacity should be measured along with plasma
cholinesterase levels. The aim of treatment is to excessive oral and respiratory secretions and
prevent respiratory failure. Adequate atropinisation is indicated by reduction of secretions.
10. Control fits with boluses of diazepam – give 10mg ivi. Diazepam is also useful for delirium and
agitation in these patients. If patient continues to fit consider midazolam infusion but patient must
be intubated. Note agitation may be due to excess atropine.
11. There is no evidence to support the use of activated charcoal or gastric lavage.
12. Remove contaminated clothing (wear gloves) and dispose of as hazardous material. Wash the
patient thoroughly with soap and water.
13. As soon as patient is stable start to reduce atropine infusion slowly over 24 hours. Infusion may
need to be increased if symptoms and signs recur.
14. Patients with minor exposure to organophosphates can be discharged if asymptomatic after 12
hours of observation.
Sources
1.
2.
South African Medical Formulary. 7th Edition.
Eddleston M, Buckely NA, Eyer P, Dawson AH. Management of acute organophosphate pesticide poisoning. Lancet.
2008;371:597-607
Approved 21st December 2008.
Review December 2009
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