## Enzyme Aging in Organophosphate Poisoning ### Definition and Mechanism **Key Point:** Aging is the loss of an alkyl group from the phosphorylated acetylcholinesterase complex, converting it from a reversible to an irreversible inhibition state. ### Timeline and Clinical Significance 1. **Initial phosphorylation:** Organophosphate binds to AChE active site (reversible) 2. **Dealkylation (aging):** One alkyl group is spontaneously lost from the phosphoryl-enzyme complex 3. **Result:** The remaining monoalkyl phosphate-enzyme complex is extremely stable and cannot be reactivated by pralidoxime ### Pralidoxime Efficacy Window - **Before aging:** Pralidoxime can reactivate AChE by removing the entire phosphoryl group - **After aging:** Pralidoxime is ineffective because the alkyl group is already lost - **Clinical window:** Typically 24–48 hours, but varies by organophosphate compound **High-Yield:** The concept of aging explains why early administration of pralidoxime (within 24–48 hours) is critical in organophosphate poisoning management. Once aging occurs, only supportive care and atropine remain effective. **Mnemonic:** **AGING = ALkyl Group Is Irreversibly Negated** — once the alkyl is gone, the enzyme cannot be reactivated. **Clinical Pearl:** Different organophosphates age at different rates. Parathion ages rapidly (hours), while malathion ages slowly (days), affecting the window for pralidoxime efficacy. [cite:Forensic Medicine & Toxicology, Reddy, Ch. Organophosphate Poisoning] 
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