Organophosphorus (OP) Poisoning
Forensic Toxicology: Cholinesterase Inhibitors
1. Mechanism of Action
OP compounds act as irreversible inhibitors of acetylcholinesterase (AChE). This leads to the accumulation of acetylcholine at muscarinic, nicotinic, and central nervous system synapses, causing a “cholinergic crisis.”
2. Clinical Manifestations (The Cholinergic Toxidrome)
| System | Clinical Findings (DUMBELS) |
|---|---|
| Muscarinic | Diarrhea, Urination, Miosis (pinpoint pupils), Bronchospasm/Bradycardia, Emesis, Lacrimation, Salivation. |
| Nicotinic | Muscle fasciculations, tremors, weakness, and respiratory failure (paralysis of the diaphragm). |
3. Management & Antidotes
- Atropine: Competitive antagonist at muscarinic receptors. Titrate until “atropinization” (clear lungs, dry secretions).
- Oximes (e.g., Pralidoxime): Regenerate the enzyme AChE. Must be administered before “aging” of the OP-AChE complex occurs.
- Decontamination: Essential for dermal exposure (remove clothing, wash skin).
4. Forensic Pearls
- Odor: Often have a characteristic “garlic-like” odor due to impurities in the manufacturing process.
- Intermediate Syndrome: A delayed onset of respiratory muscle paralysis occurring 24–96 hours after poisoning, despite initial improvement.
- Resources: For detailed clinical algorithms and board-style questions on OP poisoning management, visit mymedschool.org.