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GERD 4: Acid Suppression -- PPIs, P-CABs, and the Vonoprazan RevolutionEpisode keywords: PPI mechanism of action, vonoprazan P-CAB GERD, omeprazole equivalents potency, parietal cell proton pump H+K+ATPase, PPI safety evidence, H2 blocker tachyphylaxis, nocturnal acid breakthrough, CYP2C19 PPI metabolism, Laine vonoprazan trial 2023Episode SummaryNot all PPIs are equal, and vonoprazan is a different class of drug rather than a stronger PPI. This episode traces acid secretion from parietal cell stimulus to proton pump activation, explains why PPIs require meal timing while vonoprazan does not, quantifies potency differences across PPIs using omeprazole equivalents, and covers the Laine 2023 trial showing vonoprazan's superiority in severe erosive esophagitis. PPI safety associations from observational data are contrasted with the randomized controlled trial evidence, which largely exonerates the class.Key TopicsParietal cell physiology and the final common pathway: Three stimulants activate the proton pump. Gastrin binds CCK-2 receptors and raises intracellular calcium. Histamine binds H2 receptors and raises cAMP. Acetylcholine binds M3 receptors and raises calcium. Both calcium and cAMP trigger fusion of tubulovesicles with the canalicular membrane, exposing active H+/K+-ATPase pumps. H2 blockers interrupt only one of three pathways. PPIs and vonoprazan block the pump directly, downstream of all three stimulants regardless of what is activating the cell.H2 receptor antagonists: Available agents are cimetidine, famotidine, and nizatidine. Ranitidine was withdrawn due to NDMA (N-nitrosodimethylamine) nitrosamine contamination. H2 blockers relieve symptoms in 50 to 67% of patients. Healing rates for esophagitis are poor compared to PPIs. Tachyphylaxis limits long-term utility. Best role is mild intermittent GERD or as a bedtime add-on for nocturnal acid breakthrough, though tachyphylaxis also limits that indication over time.PPI mechanism and meal timing: PPIs are acid-labile prodrugs requiring enteric coating. After duodenal absorption, they enter the parietal cell canalicular space, get protonated in the acidic environment, and form covalent disulfide bonds with cysteine residues on active proton pumps. Only actively secreting pumps are accessible; tubulovesicle-bound pumps are invisible to PPIs. Taking PPIs 30 to 60 minutes before a meal ensures the drug arrives when the meal is stimulating maximum pump activation. Plasma half-life is approximately 90 minutes. Full steady-state suppression requires 3 to 5 days of dosing as successive pumps are inactivated. PPIs are NOT effective for acute breakthrough symptoms -- this is a board trap.CYP2C19 metabolism: Most PPIs are metabolized by CYP2C19. Poor metabolizers achieve higher drug levels and better suppression. Rapid metabolizers may have subtherapeutic levels at standard doses. Rabeprazole is least affected by CYP2C19 polymorphisms due to more non-enzymatic conversion.Omeprazole equivalents (potency at standard doses): Setting omeprazole 20 mg as 1.00: lansoprazole 15 mg is 0.90; esomeprazole 20 mg is 1.60; rabeprazole 20 mg is 1.82 (most potent standard PPI); pantoprazole 20 mg is 0.23 (roughly one-quarter the acid suppression of omeprazole 20 mg). Pantoprazole's widespread use reflects formulary economics and IV availability, not pharmacologic superiority.Nocturnal acid breakthrough: 70 to 80% of patients on twice-daily PPI still have gastric pH below 4 for more than one hour overnight. Clinical significance is often unclear -- many are asymptomatic and healing well. A bedtime H2 blocker can help short-term but tachyphylaxis limits durability. Intervention is warranted primarily when associated with persistent symptoms or non-healing esophagitis.PPI safety -- RCT evidence: Moayyedi et al., Gastroenterology 2019, randomized 17,598 patients to pantoprazole versus placebo over 3 years. No significant differences in fractures, dementia, CKD, cardiovascular events, or pneumonia. Enteric infections were modestly higher (1.4% vs 1.0%, OR 1.33). The vast majority of observational safety signals disappear when patients are properly randomized, reflecting residual confounding in population studies. Hypomagnesemia has the strongest mechanistic basis and is a class effect; monitor magnesium in long-term PPI users with symptoms or risk factors.Vonoprazan mechanism: Acid-stable, active drug (not a prodrug). No enteric coating needed. Faster absorption. Binds H+/K+-ATPase through ionic interactions with very high affinity. Critically, binds both active AND inactive pumps -- does not require a secreting pump. Half-life 7 to 9 hours versus 90 minutes for PPIs. Not significantly affected by CYP2C19 polymorphisms. Does not require meal timing. Achieves acid suppression on day 1 rather than days 3 to 5.Laine et al., Gastroenterology 2023: 1,024 patients with erosive esophagitis randomized to vonoprazan 20 mg versus lansoprazole 30 mg over 8 weeks. Overall healing: 92.9% vs 84.6% (noninferior and superior). LA-C and D subgroup: 91.7% vs 72.0%, a 19.6 percentage point difference. Vonoprazan also superior for maintenance of healing. Potency context: vonoprazan 10 mg daily approximates omeprazole 60 mg; vonoprazan 20 mg approximates omeprazole 60 mg twice daily.Board PearlsBoard trap: A patient takes their PPI when they feel heartburn and says it does not work. Correct response -- PPIs are not designed for on-demand dosing. They require 3 to 5 days to reach steady state and must be taken before meals when parietal cells are being stimulated.High-yield: Vonoprazan's three mechanistic advantages over PPIs are meal-timing independence, CYP2C19 independence, and ability to bind inactive pumps. Each traces directly to its structure as an active drug with a long half-life.Board trap: Pantoprazole is the most common IV PPI but among the weakest oral PPIs. A patient not responding to pantoprazole orally is not on the most potent available therapy. Switching to rabeprazole or esomeprazole before escalating to twice-daily dosing is a reasonable step.