pantoprazole

**Class/Mechanism:** Substituted benzimidazole PPI (-prazole). It is a prodrug, a weak base that accumulates in the acidic canaliculi of parietal cells. There it is converted to an active sulfenamide, which forms covalent disulfide bonds with cysteine residues on the H+/K+ ATPase (proton pump). This irreversibly inhibits the final common pathway of acid secretion (stimulated by histamine, ACh, and gastrin). Acid secretion returns only after new pump synthesis (about 24-48 h), so effect outlasts plasma half-life (~1 h). Pantoprazole is the most pH-stable of the PPIs and is available in IV form.

**Pharmacokinetics:** - Take 30-60 min before meals (ideally before breakfast), because pumps are most active when stimulated by food. Pumps must be actively secreting to be inhibited. - Delayed-release tablets are acid-labile, so they are enteric-coated. Do not crush them. - Hepatic metabolism via CYP2C19 (major) and CYP3A4. Pantoprazole has fewer CYP-mediated drug interactions than omeprazole. - Full effect takes about 3-5 days of dosing.

**Indications:** - GERD and erosive esophagitis - Peptic ulcer disease (gastric and duodenal) - Zollinger-Ellison syndrome (gastrinoma; high doses) - H. pylori eradication (triple/quadruple therapy: PPI + clarithromycin + amoxicillin or metronidazole; bismuth quadruple therapy) - NSAID-induced ulcer prevention or treatment - Stress ulcer prophylaxis (IV) - Upper GI bleed (high-dose IV after endoscopy)

**Adverse effects (high-yield):** - Increased risk of *C. difficile* infection (loss of gastric acid barrier) - Community-acquired pneumonia - Hypomagnesemia (can cause hypocalcemia and hypokalemia, arrhythmias, QT prolongation) - Vitamin B12 deficiency (needs acid to release B12 from food protein) and iron malabsorption - Decreased calcium absorption, with increased risk of osteoporosis and fractures (hip) - Acute interstitial nephritis and possible chronic kidney disease - Rebound acid hypersecretion after stopping (hypergastrinemia causes ECL/parietal cell hyperplasia) - Fundic gland polyps - Possible increased risk of enteric infections (Salmonella, Campylobacter)

**Drug interactions:** - Reduced absorption of drugs needing acid (ketoconazole, itraconazole, atazanavir, iron salts) - Clopidogrel is a CYP2C19-activated prodrug. Omeprazole and esomeprazole inhibit CYP2C19 and reduce its efficacy. Pantoprazole has the least effect, so it is preferred if a PPI is needed. - Methotrexate levels may rise (delayed clearance with high-dose methotrexate).

**Comparison to other acid-suppressing drugs:** - H2 blockers (ranitidine, famotidine, cimetidine) competitively block H2 receptors on parietal cells. They are less potent than PPIs. Cimetidine inhibits CYP450 and has antiandrogen effects. Tachyphylaxis can occur. - Antacids neutralize acid, with quick onset and short duration. - Sucralfate and misoprostol are mucosal protectants. Misoprostol is a PGE1 analog. - Potassium-competitive acid blockers (vonoprazan) are newer agents that reversibly block H+/K+ ATPase.

**Board pearls:** - PPIs are the most effective acid suppressors, and are first-line for GERD and PUD. - Alarm features (dysphagia, weight loss, GI bleed, anemia, age >60 with new symptoms) require endoscopy rather than empiric PPI. - Barrett esophagus is treated with long-term PPI. - Gastrin levels rise with PPI use, so hold PPIs before testing for gastrinoma, and before urea breath test or stool antigen testing for H. pylori (stop about 2 weeks before, to avoid false negatives). - Chronic PPI use can cause falsely elevated chromogranin A levels.