Organophosphate

Poisoning

Sunil Kumar Daha

Janakpur, Nepal

Organophosphorus compounds• Nerve agents:

• G agents: sarin, tabun, somanV agents: VX,VE

• Insecticides:Dimethyl compounds Diethyl

compounds • Dichlorvos• Fenthion• Malathion• Methamidophos

Diethyl compounds• Chlorpyrifos

• Diazinon

• Parathion-ethyl

• Quinalphos

Intoxication may follow ingestion, inhalation or dermal absorption.

Mechanism of toxicity

Inhibit acetyl cholinesterase causing accumulation of acetylcholine at central and peripheral cholinergic nerve endings, including neuromuscular junctions

Clinical features• onset, severity and duration of poisoning depend on the route of

exposure and agent involved

• causes an acute cholinergic phase, which may occasionally be followed by the intermediate syndrome or organophosphate-induced delayed polyneuropathy (OPIDN

• muscarinic features such as nausea, vomiting, abdominal colic, diarrhoea, sweating, hypersalivation, miosis, bronchospasm, bronchorrhea, bradycardia, urinary incontinence

• Nicotinic features such as muscle fasciculation and flaccid paresis of limb, respiratory, and occasionally, extraocular muscles

• CNS features is characterized by anxiety, slurred speech, mental status changes (e.g., delirium, coma, and seizures), and respiratory depression

Intermediate syndrome

• Occur in 20% case of OP poisoning

• Development of weakness of muscle rapidly• Spreading from ocular muscle to head and neck, proximal limbs and

muscle of respiration may leads of ventilatory failure

• May appear after 1-4 days after exposure when symptomps/signs of acute cholinergic syndrome are no longer obvious

• May last 2-3 weeks

• no specific treatment but supportive care, including maintenance of airway and ventilation,

Organophosphate-induced delayed polyneuropathy

•Rare complication

•Occur 2-3 weeks after exposure

• Mixed sensory/motor polyneuropathy

• C/F :muscle cramps followed by• numbness and paraesthesis flaccid paralysis of lower

limbs and subsequently upper limbs

General management• Maintenance of ABC

◦ Airway should be cleared of secretion◦ High flow O2◦ IV access

• Decontamination of skin◦ To prevent further absorption◦ Contaminated clothing and contact lenses removed◦ Skin washed with soap and water and eye irrigated

• Gastric lavage and activated charcoal if within 1hours

Antidotes - Atropine

• 2mg IV,repeated every 10-25 minutes until atropinization (as manifested by drying of secretions, tachycardia, flushing,dry mouth, and dilated pupils) occurs

Pralidoxime

• Dose:1-2 g for adults and 20-40 mg up to 1 g in children ,infused in NS over 5-10 minutes

• reactivates the cholinesterase and counteracts weakness, muscle fasciculations, and respiratory depression

• Treat seizures with a benzodiazepine and phenytoin; if severe seizures require muscle relaxants

References

• Davidson's Principles and Practice of Medicine 21 Edition

• Kumar and Clark 7th Edition (2009)

• Emergency Medicine,Tintinalli

Thank You