## Mechanism of PPI Action **Key Point:** PPIs are prodrugs that require activation in the acidic parietal cell canaliculus. They do NOT achieve maximal suppression within 24 hours — this is a common misconception. ### Pharmacokinetics of PPIs | Feature | Detail | | --- | --- | | **Activation site** | Acidic parietal cell canaliculus (pH < 4) | | **Active form** | Sulfenamide (formed after protonation) | | **Binding** | Irreversible to H+/K+-ATPase | | **Onset of action** | 2–3 days for maximal effect | | **Steady state** | Achieved after 3–5 days of daily dosing | | **Duration** | 24–48 hours (longer than half-life due to irreversible binding) | **High-Yield:** The delay in maximal acid suppression occurs because: 1. PPIs only affect actively secreting parietal cells 2. New parietal cells with newly synthesized pumps are not yet inhibited 3. Repeated daily dosing is needed to inhibit the entire population of pumps 4. Maximal suppression is typically achieved by day 3–5, NOT within 24 hours **Clinical Pearl:** This is why PPIs are often given for 3–5 days before assessing therapeutic efficacy in conditions like GERD or peptic ulcer disease. Patients expecting immediate relief are at risk of non-compliance. **Warning:** ~~PPIs work immediately~~ — they require 2–3 days to reach steady state and maximal effect. This is frequently tested in NEET PG. ### Why the Other Options Are Correct - **Irreversible inhibition:** PPIs covalently bind to cysteine residues on the H+/K+-ATPase, making inhibition irreversible [cite:KD Tripathi 8e Ch 50] - **Activation in acidic environment:** PPIs are weak bases that accumulate in the acidic canaliculus and are protonated to form the active sulfenamide - **Prodrug conversion:** All PPIs (omeprazole, lansoprazole, pantoprazole, rabeprazole, esomeprazole) are prodrugs requiring gastric acid for activation
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