Omeprazole is a proton pump inhibitor that requires acidic conditions in the secretory canaliculus of parietal cells for activation. The mechanism of activation is:

• A Omeprazole undergoes direct phosphorylation by the H+/K+ ATPase enzyme
• B Acidic conditions increase omeprazole's lipophilicity enabling membrane penetration to reach the ATPase
• C Low pH opens a pore in the proton pump that allows omeprazole to enter and block the ion channel
• D At acidic pH, omeprazole is converted to a tetracyclic sulfenamide that covalently binds cysteine residues on the H+/K+ ATPase ✓

Explanation

Omeprazole is a weak base (pKa 4.0) that accumulates in the acidic secretory canaliculus. Here, at pH <4, it is protonated and undergoes acid-catalyzed rearrangement first to a spiro intermediate, then to a tetracyclic sulfenamide (active form). This reactive sulfenamide forms irreversible covalent disulfide bonds with cysteine residues (Cys813, Cys892) on the luminal domain of the H+/K+ ATPase, permanently inactivating it. New acid secretion requires synthesis of new pump protein, explaining the prolonged effect despite short plasma half-life.

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

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Written and medically reviewed by the StethoPrep medical team.