A 45-year-old farmer presents to the emergency department 2 hours after accidental exposure to parathion during pesticide spraying. He exhibits severe salivation, bronchospasm, miosis, muscle fasciculations, and bradycardia. The structure marked **D** in the diagram is the site of irreversible inhibition by the organophosphate compound. Which of the following is the MOST appropriate FIRST-LINE pharmacological intervention to manage his acute muscarinic symptoms?

Explanation

## Why Atropine is right Atropine is the FIRST-LINE agent in organophosphate poisoning because it immediately blocks muscarinic receptors, counteracting the excessive acetylcholine accumulation caused by irreversible inhibition of AChE (the structure marked **D**). It rapidly controls life-threatening muscarinic symptoms (bronchospasm, bronchorrhea, salivation, bradycardia, miosis) while pralidoxime is prepared and administered. Atropine is given in repeated doses until secretions dry and signs of atropinization appear (KD Tripathi 9e, Ch 8: Anticholinergic agents and organophosphate management). ## Why each distractor is wrong - **Pralidoxime (2-PAM)**: While essential and given concurrently with atropine, it is NOT first-line because it requires time to regenerate AChE at the synaptic cleft and is only effective if given within hours before the OP-AChE bond "ages." Atropine's immediate symptomatic relief takes priority in acute management. - **Benzodiazepines**: These are reserved for seizure control and CNS manifestations (tertiary intervention), not for initial muscarinic symptom management. They are given AFTER atropine and pralidoxime are established. - **Neostigmine**: This would FURTHER inhibit AChE (the structure marked D), worsening acetylcholine accumulation and exacerbating toxicity. It is contraindicated in organophosphate poisoning. **High-Yield:** In organophosphate poisoning: **Atropine first** (symptomatic relief of muscarinic excess) → **Pralidoxime second** (enzyme regeneration) → **Benzodiazepines third** (seizure control). [cite: KD Tripathi 9e, Ch 7–8: Cholinergic agents, anticholinergic agents, and management of organophosphate poisoning]