Proton Pump Inhibitors (PPIs)

Mechanism of Action

PPIs bind irreversibly to the H+/K+-ATPase (the "proton pump") on the luminal surface of gastric parietal cells, blocking the final common pathway of acid secretion regardless of the stimulus (histamine, gastrin, or acetylcholine). Because PPIs only block active pumps, they are most effective when given 30-60 minutes before a meal, when the pumps are maximally stimulated. As their binding is irreversible, acid suppression persists until new pump protein is synthesized (typically 24-48 hours). Full effect usually takes 3-4 days of regular dosing to reach steady state. - Tintinalli's Emergency Medicine, p. 3552; Morgan & Mikhail's Clinical Anesthesiology, p. 3870

Available Agents and Standard Doses

Drug	Treatment Dose	Maintenance Dose
Omeprazole (Prilosec)	20-40 mg/day	20 mg/day
Lansoprazole (Prevacid)	15-30 mg/day	15 mg/day
Pantoprazole (Protonix)	40 mg/day	40 mg/day
Rabeprazole (Aciphex)	20 mg/day	10-20 mg/day
Esomeprazole (Nexium)	20-40 mg/day	20 mg/day
Dexlansoprazole (Dexilant)	30-60 mg/day	30 mg/day

For H. pylori eradication regimens, all PPIs are used at double-dose (twice daily). - Goldman-Cecil Medicine, p. 3169-3180; Washington Manual of Medical Therapeutics, p. 3675

Clinical Indications

GERD / erosive esophagitis - PPIs are first-line; they heal esophagitis faster and more completely than H2-receptor antagonists.
Peptic ulcer disease (PUD) - Both duodenal and gastric ulcers; used alone or combined with antibiotics for H. pylori eradication (triple therapy: PPI + clarithromycin + amoxicillin; quadruple therapy adds bismuth).
Zollinger-Ellison syndrome - High-dose PPIs are the cornerstone of medical management; conventional H2 blockers often fail.
Barrett's esophagus - Long-term PPI therapy with aspirin reduces progression to high-grade dysplasia or adenocarcinoma.
NSAID-induced ulcers - PPIs are the treatment of choice when NSAIDs must be continued.
Upper GI bleeding - Pre-endoscopy PPI therapy reduces high-risk stigmata (OR 0.67) and need for endoscopic intervention (OR 0.68); high-dose IV PPI post-endoscopy reduces rebleeding (OR 0.46, NNT 12) and need for surgery.
Stress ulcer prophylaxis - In critically ill patients.

Tintinalli's Emergency Medicine, p. 3552; Yamada's Gastroenterology; Goldman-Cecil Medicine

Pharmacokinetics

Absorption: Oral bioavailability is moderate (30-40% for omeprazole), increases with repeated dosing. Take on an empty stomach, 30-60 minutes before eating.
Metabolism: Hepatic, via cytochrome P450 (primarily CYP2C19 and CYP3A4). Dose reduction needed in severe liver impairment. Genetic polymorphisms in CYP2C19 explain significant variability in response between individuals and across ethnic populations (notably, Asian populations are often poor metabolizers, achieving higher drug levels with standard doses).
Elimination: Predominantly hepatic; renal dose adjustment is not generally needed.

Adverse Effects and Long-Term Risks

PPIs are generally well tolerated for short-term use. The main adverse effects with long-term use are:

Adverse Effect	Notes
Hypomagnesemia	PPIs impair intestinal Mg2+ absorption; recognized cause of refractory hypomagnesemia
C. difficile infection	Altered gastric pH promotes colonization; PPI use is an independent risk factor
Community-acquired pneumonia	Higher gastric pH allows bacterial overgrowth and aspiration
Bone fractures	Possibly related to impaired Ca2+ absorption in achlorhydric environment
Chronic kidney disease	Associated in observational studies; mechanism unclear
Vitamin B12 deficiency	Impaired cleavage of protein-bound B12 in achlorhydria
Enterochromaffin-like (ECL) cell hyperplasia	From elevated gastrin due to acid suppression; significance uncertain
Rebound acid hypersecretion	On abrupt discontinuation; taper over weeks, replacing with H2RA or antacids

Tintinalli's Emergency Medicine, p. 3552; Morgan & Mikhail, p. 3880; National Kidney Foundation Primer

Drug Interactions

Clopidogrel: All PPIs (especially omeprazole, esomeprazole) inhibit CYP2C19, reducing conversion of clopidogrel to its active metabolite - potentially blunting antiplatelet effect. This is an important cardiology consideration. A recent 2025 meta-analysis (PMID 40685887) found clopidogrel + PPI combination remains clinically acceptable with attention to GI bleeding risk.
Warfarin, diazepam, phenytoin: PPIs can decrease hepatic clearance via P450 inhibition, leading to drug accumulation.
Drugs requiring acid for absorption: Ketoconazole, itraconazole, iron salts, atazanavir - their absorption is reduced in the higher-pH environment.

Dosing Pearls

Take 30-60 minutes before the first meal of the day for maximum efficacy.
For H. pylori eradication: Standard PPI doses are omeprazole 20 mg, lansoprazole 30 mg, pantoprazole 40 mg - all given twice daily.
High-dose IV PPI for upper GI bleed: 80 mg bolus then 8 mg/hour for 72 hours post-endoscopy, per ACG and International Consensus guidelines.
Zollinger-Ellison syndrome may require doses 3-10x standard.

Comparison With H2 Receptor Antagonists

Feature	PPIs	H2RAs
Mechanism	Irreversible H+/K+-ATPase block	Competitive histamine-H2 receptor block
Onset	30-60 min (full effect 3-4 days)	1-3 hours
Acid suppression	~90-95% reduction	~70% reduction
Ulcer healing	Faster	Slower
Tolerance	Not significant	Develops with chronic use
Rebound	Yes, on discontinuation	Yes

Emerging Alternative: Potassium-Competitive Acid Blockers (P-CABs)

Vonoprazan (and revaprazan, tegoprazan) are a newer class that competitively block the potassium-binding site of H+/K+-ATPase, unlike PPIs which require acid activation. P-CABs are acid-stable, have a faster onset (day 1 effect), higher bioavailability unaffected by food, and are approved in Japan, Korea, and increasingly elsewhere. Vonoprazan has been approved in the US and shows non-inferiority to PPIs for healing erosive GERD and peptic ulcers. - Sleisenger & Fordtran's GI and Liver Disease; Harrison's Principles of Internal Medicine 22E (2025)

Recent evidence note: A 2025 Cochrane review (PMID 40066936) found insufficient evidence to support PPI use for GERD in preterm infants - caution is warranted in pediatric populations.

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