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Here is a comprehensive overview of Proton Pump Inhibitors (PPIs) drawn from Goodman & Gilman's Pharmacological Basis of Therapeutics, Goldman-Cecil Medicine, and Yamada's Textbook of Gastroenterology.
Proton Pump Inhibitors (PPIs)
Overview
PPIs are the most potent suppressors of gastric acid secretion available. They inhibit the gastric H+/K+-ATPase (the proton pump) and reduce daily acid production (basal and stimulated) by 80-95%.
Available Agents and Doses
| Drug | Standard Dose | Maintenance Dose |
|---|---|---|
| Omeprazole | 20-40 mg/day | 20 mg/day |
| Lansoprazole | 15-30 mg/day | 15 mg/day |
| Pantoprazole | 40 mg/day | 40 mg/day |
| Rabeprazole | 20 mg/day | 10-20 mg/day |
| Esomeprazole (S-isomer of omeprazole) | 20-40 mg/day | 20 mg/day |
| Dexlansoprazole (R-enantiomer of lansoprazole) | 30-60 mg/day | 30 mg/day |
All PPIs have equivalent efficacy at comparable doses.
Mechanism of Action
PPIs are prodrugs that require activation in an acid environment. Here is the step-by-step mechanism:
- Oral PPI is absorbed in the small bowel and enters systemic circulation
- It diffuses into gastric parietal cells and concentrates in the acidic secretory canaliculi
- Proton-catalyzed conversion forms a tetracyclic sulfenamide (active form), trapping the drug in the canaliculus
- The activated sulfenamide binds covalently to sulfhydryl groups of cysteines on the H+/K+-ATPase
- This irreversibly inactivates the pump - acid secretion resumes only when new pumps are synthesized (24-48 hours)
Because PPIs block the final common step in acid production, they suppress all stimulated acid (histamine, gastrin, acetylcholine pathways) as well as basal secretion.
Activation of a PPI (omeprazole) from its prodrug form. The sulfenamide reacts covalently with sulfhydryl groups on the proton pump, irreversibly inhibiting it. - Goodman & Gilman's, Fig. 53-2
Pharmacokinetics (ADME)
- Take 30 min before a meal - food stimulates acid production, which activates the prodrug in the canaliculus
- Rapidly absorbed in the small bowel; highly protein bound
- Extensively metabolized by CYP2C19 and CYP3A4
- Plasma t½ is short (~0.5-3 h), but acid suppression lasts 24-48 h due to irreversible pump binding
- Full effect takes 2-5 days (not all pumps are active simultaneously; once-daily dosing takes time to reach steady-state ~70% inhibition)
- Formulations protect against acid degradation in the stomach:
- Enteric-coated pellets (e.g., rabeprazole)
- Delayed-release tablets (lansoprazole, pantoprazole, rabeprazole)
- Delayed-release capsules (dexlansoprazole, esomeprazole, omeprazole, lansoprazole)
- IV forms available: esomeprazole sodium, omeprazole sodium, pantoprazole
CYP2C19 polymorphisms: Asians (25-30%) and Oceanians (~60%) are more likely to be poor metabolizers of PPIs vs. ~15% of Caucasians or Africans. Poor metabolizers achieve higher plasma levels - may require dose reduction for chronic use.
Clinical Indications
| Indication | Notes |
|---|---|
| GERD / Erosive esophagitis | First-line; superior to H2 blockers |
| Peptic ulcer disease (gastric & duodenal) | Promotes healing |
| H. pylori eradication | Used alongside antibiotics (triple/quadruple therapy) |
| Zollinger-Ellison syndrome | Drug of choice; controls hypersecretion in >95% |
| NSAID-associated ulcers | Prevention and treatment (lansoprazole, pantoprazole, esomeprazole approved) |
| GI bleeding (peptic ulcer) | High-dose IV PPI post-endoscopy reduces rebleeding and need for surgery |
For upper GI bleeding: IV esomeprazole 80 mg bolus then 8 mg/h for ~72 h after endoscopic hemostasis reduces rebleeding from 10.3% to 5.9%.
Drug Interactions
- Clopidogrel: PPIs (especially omeprazole) inhibit CYP2C19 conversion of clopidogrel to its active form. Pantoprazole is least likely to cause this interaction. Concurrent PPI + clopidogrel use significantly reduces GI bleeding without increasing adverse cardiac events.
- Warfarin: Interaction with esomeprazole, lansoprazole, omeprazole, rabeprazole
- Diazepam: Esomeprazole, omeprazole (increased levels)
- Atazanavir/Nelfinavir: Reduced absorption with all PPIs (avoid co-use with HIV antiretrovirals)
- Methotrexate: PPIs inhibit methotrexate elimination → elevated MTX levels (toxicity risk)
- Omeprazole specifically: Inhibits CYP2C19 (raises phenytoin, disulfiram levels) and induces CYP1A2 (increases clearance of theophylline, imipramine, antipsychotics)
Adverse Effects
Common (generally well-tolerated):
- Headache, nausea, abdominal pain, flatulence, constipation, diarrhea
Long-term / serious concerns:
- Hypomagnesemia (chronic use)
- Vitamin B12 deficiency (decreased absorption; clinical relevance not fully established)
- Fracture risk - decreased calcium absorption may reduce bone density
- Hypergastrinemia - secondary to acid suppression; may promote gastric polyposis and atrophic gastritis
- Rebound acid hypersecretion on discontinuation (can cause dyspepsia)
- Clostridium difficile and other GI infections (higher gastric pH reduces barrier)
- Small intestinal bacterial overgrowth (SIBO)
- Possible associations (not yet confirmed by prospective trials): chronic kidney disease, dementia
- COVID-19: Dose-dependent relationship between PPI use and more severe infection/secondary infections
Key Clinical Pearls
- Take 30-60 min before the first meal for optimal activation
- Pantoprazole is preferred when co-prescribing with clopidogrel
- Asian patients may need lower doses chronically due to CYP2C19 polymorphisms
- Don't use alongside atazanavir (reduced HIV drug absorption)
- Discontinuation after prolonged use should be gradual to avoid rebound hypersecretion
- PPI use should be limited to the lowest effective dose and only when clinically indicated
Sources: Goodman & Gilman's The Pharmacological Basis of Therapeutics, Chapter 53; Goldman-Cecil Medicine, Chapter 124-125; Yamada's Textbook of Gastroenterology
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