🧪 Chapter 121: Organophosphate & Carbamate Poisoning

Acetylcholinesterase inhibition · Cholinergic toxidrome (SLUDGE, DUMBELS) · Nicotinic (muscle fasciculations, weakness) · CNS (seizures) · Atropine (muscarinic) · Pralidoxime (2-PAM) · Ageing · Intermediate syndrome · Carbamates (no oximes)

🔍 Core Concepts: Organophosphate & Carbamate Poisoning

📌 Mechanism
Irreversible (OP) or reversible (carbamate) inhibition of acetylcholinesterase → acetylcholine accumulation → cholinergic excess. Ageing: covalent binding within 24-48h makes OP resistant to oximes.
⚠️ Clinical Features (SLUDGE/DUMBELS)
Salivation, Lacrimation, Urination, Defecation, GI upset, Emesis; also miosis, bronchorrhoea, bronchospasm, bradycardia, muscle fasciculations, weakness, seizures.
💊 Atropine (Muscarinic Antidote)
Competitive antagonist at muscarinic receptors. Dose: 0.05 mg/kg IV q5-10 min, double dose until drying of secretions. No maximum dose. Tachycardia NOT a contraindication.
🔄 Pralidoxime (2-PAM, Nicotinic Antidote)
Reactivates acetylcholinesterase before ageing. Dose: 25-50 mg/kg bolus then 10 mg/kg/h infusion. For OP poisoning, NOT for carbamates (ineffective).
🧪 Carbamate Poisoning
Reversible cholinesterase inhibition. Atropine may be needed. Do NOT use pralidoxime (oximes not effective, may worsen toxicity).
📉 Intermediate Syndrome
1-4 days after acute OP poisoning: proximal muscle weakness, respiratory failure, cranial nerve palsies. Treat with respiratory support, continue oximes.

🩺 Stepwise Approach: Organophosphate Poisoning

1
Decontamination & PPE
Remove clothing, wash skin with soap and water. Healthcare providers must wear gloves, gown, mask (avoid secondary exposure). Avoid gastric lavage (risk of aspiration).
2
ABCs & airway protection
Excessive secretions → suction, intubate early if respiratory distress. Avoid succinylcholine (prolonged paralysis due to pseudocholinesterase inhibition). Use rocuronium if needed.
3
Atropine (life-saving antidote)
Start with 0.05 mg/kg IV. Double dose every 5-10 minutes until muscarinic signs resolve (drying of secretions, clear lungs, HR >80). No maximum dose. Continue infusion at 10-20% of total bolus dose per hour.
4
Pralidoxime (2-PAM, for OP only)
Give 25-50 mg/kg IV over 30 min, then 10 mg/kg/h infusion. Best within 24h (before ageing). NOT for carbamate poisoning. Continue until clinical recovery or 7 days.
5
Seizure management
Benzodiazepines (midazolam, lorazepam, diazepam) first-line. Seizures refractory to benzodiazepines may require phenobarbitone or propofol.
6
Monitor & treat complications
Intermediate syndrome (1-4d): respiratory weakness → ventilatory support. Watch for aspiration pneumonia, pancreatitis. RBC cholinesterase level <50% of baseline suggests significant exposure.