Proton pump inhibitors (PPIs) like omeprazole require acid environment for activation. Which pharmacokinetic property explains why PPIs must be taken before meals?

• A Meal-induced bile flow increases duodenal pH, improving PPI absorption from the small intestine
• B PPIs are prodrugs that accumulate in the acidic canalicular space of parietal cells only when H+/K+-ATPase proton pumps are actively secreting acid; meal stimulation activates pumps and recruits them to the canalicular surface, maximizing drug activation and irreversible enzyme binding ✓
• C Food delays gastric emptying, prolonging PPI contact time with gastric mucosa for local effect
• D PPIs require pre-activation by pepsin secreted during meals before they can inhibit H+/K+-ATPase

Explanation

PPIs are acid-labile prodrugs that are enteric-coated to avoid premature activation in the stomach. After absorption, they selectively concentrate in the highly acidic secretory canaliculus of the parietal cell, where low pH protonates and converts them to the active sulfenamide (or sulfenic acid) form that irreversibly alkylates cysteine residues (Cys813, Cys892) on H+/K+-ATPase. H+/K+-ATPase pumps are only inserted into the canalicular membrane and actively pumping when stimulated by meals (gastrin, histamine, acetylcholine); therefore taking a PPI 30–60 minutes before the first meal of the day maximizes the pool of active pumps available for drug inhibition.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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