---

1. DEFINITION & SPECTRUM

---

2. NORMAL MUCOSAL DEFENSE vs. AGGRESSIVE FACTORS

• Hydrochloric acid (HCl) and pepsin
• Helicobacter pylori infection
• NSAIDs and aspirin (COX inhibition → ↓ prostaglandin → ↓ mucus, ↓ bicarbonate, ↓ mucosal blood flow)
• Bile reflux, alcohol, cigarette smoking

• Mucus-bicarbonate barrier (pH gradient 7 at surface → 1–2 at lumen)
• Tight junctions between epithelial cells
• Mucosal blood flow (delivers O₂, bicarbonate, removes acid)
• Prostaglandins (PGE₂, PGI₂) → stimulate mucus and bicarbonate secretion
• Rapid epithelial restitution after injury

A peptic ulcer forms when either excess acid/pepsin production overwhelms normal defenses, or mucosal defenses are impaired — or both. — Guyton & Hall Medical Physiology

---

3. PEPTIC ULCER DISEASE (PUD)

Epidemiology

• Affects >4 million individuals/year in the United States
• Lifetime risk: ~10% in males, ~4% in females
• Most common sites: gastric antrum and first portion of the duodenum

Pathogenesis

• Found in >75% of PUD cases; >70% of all PUD associated with it
• H. pylori physically burrows through the mucous barrier, releases urease (producing ammonium → liquefies mucus), stimulates gastric acid secretion, triggers chronic inflammation
• Only 5–10% of infected individuals develop ulcers — host factors and strain virulence (CagA, VacA) matter

• Inhibit COX-1 → suppress prostaglandin synthesis → ↓ mucus, ↓ bicarbonate, ↓ mucosal blood flow
• Becoming the leading cause of gastric ulcers in the US as H. pylori rates fall
• Risk amplified by: concurrent anticoagulant use, age >65, prior ulcer history

• Zollinger-Ellison syndrome: gastrin-secreting tumors → massive acid → multiple ulcers in stomach, duodenum, and jejunum
• Parietal cell hyperplasia, excessive secretory responses

• Cigarette smoking (↓ mucosal blood flow, ↓ healing)
• High-dose corticosteroids (suppress prostaglandin synthesis)
• Alcohol-related cirrhosis, chronic renal failure, hyperparathyroidism (↑ Ca²⁺ → ↑ gastrin → ↑ acid)

Clinical Features of PUD

Complications

Diagnosis

• Endoscopy (EGD): gold standard; biopsy for H. pylori and malignancy
• Urea breath test: non-invasive H. pylori detection (urease-based)
• Stool antigen test: H. pylori detection, also useful for post-treatment confirmation
• Serology: detects anti-H. pylori IgG (less useful — cannot distinguish active vs past infection)
• Barium upper GI series: "crater" or niche sign

---

4. GASTROESOPHAGEAL REFLUX DISEASE (GERD)

• Retrograde passage of gastric contents → esophageal mucosal damage
• Core mechanism: transient lower esophageal sphincter (LES) relaxations; exacerbated by ↑ intra-abdominal pressure, hiatus hernia, ↓ esophageal clearance
• Symptoms: heartburn, regurgitation, dysphagia, atypical features (hoarseness, chronic cough, asthma)
• Complications: erosive esophagitis, Barrett's esophagus, esophageal adenocarcinoma
• Management: lifestyle modification → step-up to H2 blockers → PPIs → antireflux surgery (Nissen fundoplication)

---

5. PHARMACOLOGY OF ACID PEPTIC DISORDERS

5A. ANTACIDS

---

5B. H₂-RECEPTOR ANTAGONISTS (H2RAs)

• Well-absorbed orally; cimetidine & famotidine ~50% bioavailability (first-pass)
• Cleared by hepatic metabolism + renal excretion; dose reduce in renal failure
• Half-lives: 1.1–4 hours; duration of action dose-dependent

1. Mild-moderate GERD (infrequent heartburn)
2. Acute peptic ulcer (largely superseded by PPIs)
3. Non-ulcer dyspepsia
4. Prevention of stress-related gastritis in ICU patients
5. Prophylaxis before procedures, OTC heartburn relief

• Very safe overall (<3% adverse events): diarrhea, headache, fatigue, myalgias
• Cimetidine-specific: gynecomastia, impotence, galactorrhea (anti-androgenic; inhibits androgen receptors and estradiol metabolism); mental confusion in elderly/ICU; inhibits CYP1A2, 2C9, 2D6, 3A4 — many drug interactions
• Rapid IV infusion → bradycardia, hypotension (cardiac H₂ blockade) — infuse over 30 min
• Cross placenta, secreted in breast milk

---

5C. PROTON PUMP INHIBITORS (PPIs)

"Since their introduction in the late 1980s, these efficacious acid inhibitory agents have assumed the major role for the treatment of acid-peptic disorders. PPIs are now among the most widely prescribed drugs worldwide." — Katzung's, 16th ed

1. PPIs are inactive prodrugs — substituted benzimidazoles
2. Acid-resistant enteric-coated formulations absorbed in the small intestine
3. After absorption, as lipophilic weak bases (pKa 4–5), they diffuse across membranes and accumulate in the acidic parietal cell canaliculus (>1000-fold concentration by Henderson-Hasselbalch trapping)
4. Protonation → rapid conversion to sulfenamide cation (active form)
5. Covalent disulfide bond with H⁺/K⁺-ATPase (proton pump) → irreversible inhibition
6. Acid secretion resumes only when new pump molecules are synthesized (t½ ~18 h)

1. GERD (first-line for erosive esophagitis, superior to H2RAs)
2. PUD — 4–8 weeks; superior ulcer healing vs H2RAs
3. H. pylori eradication (component of triple/quadruple therapy)
4. Zollinger-Ellison syndrome (high-dose, long-term)
5. NSAID-induced ulcer prevention (when NSAID cannot be discontinued)
6. Stress ulcer prophylaxis in critically ill patients

• Generally very safe short-term
• Long-term concerns:
  • ↑ Serum gastrin (1.5–2× normal; ECL hyperplasia; rebound acid secretion on abrupt discontinuation)
  • Hypomagnesemia (with >1 year use)
  • ↓ Bone density → ↑ hip/spine fracture risk
  • Clostridium difficile infection (↑ with acid suppression)
  • Community-acquired pneumonia (slightly ↑ risk)
  • Vitamin B12 and iron malabsorption (requires gastric acid for absorption)
  • Benign gastric fundic-gland polyps

• Clopidogrel + PPIs (especially omeprazole/esomeprazole): PPIs inhibit CYP2C19 → ↓ clopidogrel activation → ↓ antiplatelet effect. Use pantoprazole or rabeprazole if needed.
• ↓ Absorption of ketoconazole, itraconazole, atazanavir (need acidic environment)
• Omeprazole: inhibits warfarin, diazepam, phenytoin metabolism
• All food reduces bioavailability ~50% — take on empty stomach

---

5D. MUCOSAL PROTECTIVE AGENTS

Sucralfate

• Mechanism: Sucrose complexed to sulfated aluminum hydroxide; in acidic conditions forms a viscous paste that binds selectively to ulcer bases (positively charged proteins in ulcer base), forming a physical protective barrier for up to 6 hours. Also stimulates mucosal prostaglandin and bicarbonate secretion.
• Dose: 1 g four times daily on empty stomach
• Use: Stress ulcer prophylaxis in ICU; useful when avoiding acid-inhibitory therapy
• Adverse effects: Constipation (2%); avoid in renal failure (aluminum accumulation)
• Interactions: Can bind and reduce absorption of other drugs — space administration

Misoprostol (PGE₁ analog)

• Mechanism: Binds mucosal prostaglandin receptors → ↑ mucus, ↑ bicarbonate, ↑ mucosal blood flow + inhibits acid secretion (↓ cAMP in parietal cells)
• Use: Prevention of NSAID-induced gastric ulcers (indicated when NSAIDs cannot be stopped in high-risk patients)
• Dose: 200 µg four times daily
• Adverse effects: Dose-dependent diarrhea and cramping (limits use); contraindicated in pregnancy (uterotonic — induces contractions)
• Half-life: <30 minutes; must dose 3–4 times daily

Bismuth subsalicylate

• Mechanism: Coating agent; forms a protective layer; has direct anti-H. pylori bactericidal activity (disrupts bacterial cell wall)
• Use: Component of bismuth quadruple therapy for H. pylori; traveler's diarrhea
• Adverse effects: Black discoloration of stool and tongue (bismuth sulfide), tinnitus (salicylate toxicity in high doses)

---

5E. H. PYLORI ERADICATION THERAPY

• In areas of clarithromycin resistance >15% or unknown: use bismuth quadruple therapy
• Avoid clarithromycin in patients with prior macrolide exposure

• Levofloxacin-based triple: PPI + Levofloxacin + Amoxicillin × 10 days
• Rifabutin-based: PPI + Rifabutin + Amoxicillin × 10 days (~86% cure in resistant strains)
• Culture & sensitivity testing if two courses fail

1. Antibiotic-resistant strains (clarithromycin resistance ~13–16% in US)
2. Inadequate acid suppression
3. Non-adherence

---

5F. POTASSIUM-COMPETITIVE ACID BLOCKERS (P-CABs)

• Binds to the potassium-binding site of H⁺/K⁺-ATPase competitively and reversibly
• Does not require acid activation (unlike PPIs) → faster, more consistent acid suppression
• Not pH-dependent for activation → can be taken with or without food
• Used in H. pylori eradication regimens and PUD

---

6. SUMMARY COMPARISON TABLE

---

• Katzung's Basic and Clinical Pharmacology, 16th Edition — Chapter 62
• Guyton and Hall Textbook of Medical Physiology, 14th Edition — Chapter 67
• Robbins & Kumar Basic Pathology — Chapter 13
• Harrison's Principles of Internal Medicine, 22nd Edition — Chapter 335
• Yamada's Textbook of Gastroenterology, 7th Edition — Chapters 49, 50
• Sleisenger and Fordtran's Gastrointestinal and Liver DiseaseThe above is a comprehensive, textbook-sourced reference on acid peptic disorders. Here's a quick orientation to the sections:

1. Spectrum of APD — PUD, GERD, stress ulcers, Zollinger-Ellison, dyspepsia
2. Pathophysiology — the offensive vs. defensive balance, how H. pylori destroys the mucosal barrier, how NSAIDs inhibit prostaglandin protection
3. Clinical features — classic symptom patterns of duodenal vs. gastric ulcers, plus complications (hemorrhage, perforation, obstruction, malignancy)
4. Diagnosis — endoscopy, urea breath test, stool antigen, barium studies

• Antacids — types (NaHCO₃, CaCO₃, Mg/Al hydroxides), mechanisms, adverse effects, interactions
• H2-receptor antagonists — cimetidine, famotidine, nizatidine; mechanism, dosing table, CYP interactions, cimetidine-specific effects (gynecomastia, multiple drug interactions)
• PPIs — all 6 agents; irreversible H⁺/K⁺-ATPase blockade mechanism; pharmacokinetics table; clinical uses; long-term risks (hypomagnesemia, fractures, C. diff, B12 deficiency); clopidogrel interaction warning
• Mucosal protective agents — sucralfate (physical barrier + prostaglandin stimulation), misoprostol (PGE₁ analog), bismuth
• H. pylori eradication — triple therapy, bismuth quadruple, clarithromycin resistance guidance, salvage regimens
• P-CABs (Vonoprazan) — newer class with advantages over PPIs