All of the following are true regarding proton pump inhibitors EXCEPT:

Explanation

## Mechanism of PPI Action **Key Point:** Proton pump inhibitors (PPIs) are prodrugs that require activation in the acidic parietal cell canaliculus, not rapid systemic absorption. ### PPI Pharmacokinetics | Property | Detail | |----------|--------| | **Prodrug status** | Inactive in neutral pH; activated only in acidic environment | | **Activation site** | Parietal cell canaliculus (not stomach lumen) | | **Metabolism** | Hepatic via CYP3A4 and CYP2C19 | | **Onset of action** | Delayed: 2–3 days for maximal effect | | **Target** | H+/K+-ATPase (irreversible inhibition) | **High-Yield:** PPIs have a **delayed onset of 2–3 days** for maximal acid suppression, not 30 minutes. This is because: 1. They must be absorbed intact (as prodrugs) 2. Hepatic activation via CYP enzymes is required 3. The irreversible binding means new parietal cells must be synthesized to restore acid secretion **Clinical Pearl:** Patients often require bridging with H₂ blockers or antacids for the first 24–48 hours because PPI effect is not immediate. **Warning:** The rapid onset myth is a common trap — PPIs are NOT fast-acting agents like H₂ blockers or antacids. ### Why the Other Statements Are Correct - **Irreversible inhibition of H+/K+-ATPase:** True — PPIs covalently bind the proton pump, requiring new enzyme synthesis for recovery. - **Prodrugs activated in acidic environment:** True — they are inactive at physiologic pH and only become active in the stomach's acidic milieu. - **Hepatic metabolism via CYP3A4/2C19:** True — this is why PPIs have significant drug interactions (e.g., with clopidogrel, warfarin).