A 32-year-old farmer from Punjab is brought to the emergency department 45 minutes after accidental exposure to an organophosphate pesticide during crop spraying. He is conscious but severely distressed. Vital signs: HR 52/min, BP 140/90 mmHg, RR 28/min, SpO₂ 88% on room air. Physical examination reveals pinpoint pupils, profuse salivation, bronchospasm with audible crackles bilaterally, muscle fasciculations, and urinary incontinence. Serum cholinesterase level is 25% of normal. What is the immediate pharmacological management priority?

Explanation

## Immediate Management of Organophosphate Poisoning **Key Point:** Atropine is the first-line antidote in organophosphate poisoning and must be given aggressively and early, before pralidoxime. ### Mechanism of Organophosphate Toxicity Organophosphates irreversibly inhibit acetylcholinesterase, causing accumulation of acetylcholine at muscarinic and nicotinic receptors, leading to a cholinergic crisis. ### Atropine: Why First? 1. **Muscarinic antagonist** — blocks excessive acetylcholine at muscarinic receptors (salivation, bronchospasm, bradycardia, miosis) 2. **Rapid onset** — works within minutes 3. **Life-saving** — reverses respiratory depression and bronchospasm immediately 4. **Titration** — given in repeated boluses (2–5 mg IV every 5–10 minutes) until signs of atropinization appear (dry mouth, dilated pupils, tachycardia) **High-Yield:** Atropine does NOT reverse nicotinic effects (muscle fasciculations, paralysis, weakness) — that is the role of pralidoxime. ### Pralidoxime (2-PAM): Why Second? - **Oxime reactivator** — reactivates acetylcholinesterase by removing the phosphoryl group (only effective if given early, before "aging" of the enzyme) - **Nicotinic antagonist** — reverses muscle weakness and fasciculations - **Timing** — should be given after atropine has stabilized the airway and breathing, typically within 24–48 hours of exposure (efficacy decreases with time) - **Dose** — 1 g IV over 5–30 minutes, then 500 mg every 4–6 hours ### Clinical Pearl The patient's SpO₂ of 88% with bronchospasm is a medical emergency. Atropine must be given immediately to reverse bronchospasm and allow adequate oxygenation. Pralidoxime is important but secondary in the acute phase. ### Mnemonic: SLUDGE (Muscarinic Signs) **S** — Salivation **L** — Lacrimation **U** — Urination **D** — Defecation **G** — GI upset **E** — Emesis All reversed by atropine. ### Supportive Care - Airway management and mechanical ventilation if needed - Oxygen supplementation - Seizure prophylaxis with benzodiazepines (diazepam or lorazepam) if indicated - Decontamination (remove clothing, wash skin) - Avoid depolarizing muscle relaxants (succinylcholine) — use non-depolarizing agents if intubation required