## Enzyme Aging in Organophosphate Poisoning ### Definition of Aging Aging is the process by which the phosphorylated acetylcholinesterase complex undergoes a conformational change, losing an alkyl group and becoming **irreversibly** bound to the enzyme. Once aged, the enzyme cannot be reactivated by pralidoxime. ### Timeline of Aging | Organophosphate Class | Time to Aging | Clinical Implication | | --- | --- | --- | | Malathion, parathion | 6–12 hours | Pralidoxime effective if given early | | Sarin (nerve agent) | 1–2 minutes | Extremely rapid aging | | Chlorpyrifos | 12–24 hours | Longer window for reactivation | **Key Point:** For **most agricultural organophosphates** (malathion, parathion, monocrotophos), aging occurs within **6–12 hours**. This is the critical window for pralidoxime administration. **High-Yield:** Pralidoxime is only effective **before** aging occurs. Once aging is complete, atropine becomes the sole symptomatic treatment. **Clinical Pearl:** In practice, pralidoxime should be given as soon as possible (ideally within 2–4 hours) to maximize reactivation before aging progresses. Delayed presentation (>12 hours) may result in a poor prognosis despite antidote therapy. **Mnemonic:** **AGING = Alkyl loss + Irreversible binding** — remember that aging is a one-way process. 
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