GI Pharmacology: Drugs for Peptic Ulcer

Introduction/Overview

Peptic ulcer disease (PUD) remains a significant gastrointestinal disorder worldwide, characterized by mucosal erosion in the stomach or duodenum. Historically, ulcerogenic factors such as Helicobacter pylori infection and non‑steroidal anti‑inflammatory drug (NSAID) use have been recognized, yet the pharmacologic management continues to evolve. This chapter provides a systematic examination of therapeutic agents employed in PUD, including their classification, pharmacodynamics, pharmacokinetics, clinical applications, safety profiles, and practical prescribing considerations.

Learning objectives:

• Identify the principal drug classes used in peptic ulcer therapy and their chemical features.
• Explain the mechanisms by which acid‑suppressive and mucosal protective agents mitigate ulcer formation and promote healing.
• Describe the pharmacokinetic properties that influence dosing strategies for each drug class.
• Recognize common adverse effects, contraindications, and drug interactions associated with peptic ulcer pharmacotherapy.
• Apply knowledge of special patient populations to optimize therapeutic outcomes.

Classification

Acid‑Suppressive Agents

Acid‑suppressive therapy constitutes the cornerstone of PUD treatment. Agents are grouped into four principal categories:

• Proton pump inhibitors (PPIs)
• Histamine‑2 receptor antagonists (H2RAs)
• Antacids and buffer agents
• Sucralfate, a mucosal protective compound

Chemical Classification of PPIs

PPIs share a common pharmacophore comprising a substituted benzene ring linked to a sulfinyl or sulfonyl moiety and a pyridine or pyrimidine group. Structural diversity arises from variations in the side chain attached to the sulfinyl group, influencing acid‑stability and metabolic pathways. Representative compounds include omeprazole, esomeprazole, lansoprazole, pantoprazole, and rabeprazole.

H2RAs Chemical Structure

H2RAs possess an imidazole core and a side chain containing a tertiary amine. Variations in the aromatic ring substituents affect receptor affinity and metabolic stability. Common H2RAs are ranitidine, famotidine, cimetidine, and nizatidine.

Antacids and Buffer Agents

Antacids are typically metal hydroxides (e.g., magnesium hydroxide, aluminum hydroxide) or carbonate salts that neutralize gastric acid. Buffer agents such as sodium bicarbonate provide transient pH elevation by forming bicarbonate ions.

Sucralfate

Sucralfate is an aluminum salt of a synthetic polysaccharide. It polymerizes upon contact with acidic pH, forming a viscous protective barrier over ulcerated mucosa.

Mechanism of Action

Proton Pump Inhibitors

PPIs irreversibly inhibit the H⁺/K⁺-ATPase (the gastric proton pump) located on parietal cell secretory membranes. Binding to a cysteine residue on the sulfhydryl group of the enzyme leads to covalent inhibition, resulting in a profound reduction of gastric acid secretion. The effect requires activation in the acidic environment of the parietal cell canaliculi; thus, therapeutic onset is delayed until the drug accumulates in the gastric lumen and reaches the parietal cell surface. Because the inhibition is irreversible, new proton pumps must be synthesized for acid secretion to resume, accounting for the sustained action lasting approximately 24 hours.

Histamine‑2 Receptor Antagonists

H2RAs competitively bind to H₂ receptors on parietal cells, blocking histamine‑mediated stimulation of the adenylate cyclase pathway. This inhibition reduces intracellular cyclic adenosine monophosphate (cAMP) levels, thereby decreasing activation of the H⁺/K⁺-ATPase and overall gastric acid output. H2RAs exhibit a dose‑dependent but reversible effect, with a shorter duration of action than PPIs.

Antacids and Buffer Agents

Antacids directly react with hydrochloric acid (HCl) in the stomach, forming water and corresponding salts (e.g., MgCl₂, AlCl₃). The neutralization raises gastric pH transiently, alleviating acid‑related symptoms. Buffer agents generate bicarbonate ions upon dissolution, which combine with HCl to produce carbon dioxide (CO₂) and water, thereby increasing luminal pH. These agents provide only symptomatic relief without influencing acid secretion pathways.

Sucralfate

Sucralfate’s mechanism involves adsorption to ulcerated mucosal surfaces in low pH environments, forming a viscous, adhesive barrier. This barrier protects the ulcer base from acid, pepsin, and bile salts, thereby facilitating epithelial regeneration. Additionally, sucralfate may stimulate prostaglandin synthesis, further promoting mucosal defense.

Pharmacokinetics

Absorption

PPIs are administered orally in enteric‑coated capsules to prevent premature dissolution in the acidic stomach. Upon reaching the small intestine, the coating dissolves, releasing the active drug. Bioavailability for most PPIs ranges from 20% to 40%, depending on formulation and food intake; co‑administration with food can enhance absorption for some agents. H2RAs exhibit high oral bioavailability, generally exceeding 80%. Antacids are poorly absorbed; their systemic exposure is minimal. Sucralfate is poorly absorbed (<1%) because of its high molecular weight and polymeric nature.

Distribution

PPIs are extensively protein‑bound (>90%) primarily to albumin. They distribute into the gastric mucosa, where they exert therapeutic activity. H2RAs are also highly protein‑bound (70–90%) and penetrate tissues, including the gastric mucosa. Antacids and sucralfate remain largely confined to the gastrointestinal tract due to low plasma concentrations.

Metabolism

PPIs undergo hepatic metabolism predominantly via cytochrome P450 (CYP) isoenzymes, chiefly CYP2C19 and CYP3A4. Genetic polymorphisms in CYP2C19 can lead to variable drug exposure; poor metabolizers may experience increased acid suppression. H2RAs are metabolized in the liver, with diverse pathways: cimetidine, for example, is eliminated via hepatic metabolism and renal excretion, whereas famotidine undergoes minimal hepatic metabolism and is largely renally cleared. Antacids are not significantly metabolized. Sucralfate is not metabolized and is excreted unchanged in the feces.

Excretion

PPIs are eliminated through biliary excretion and renal clearance. The terminal elimination half‑life (t_1/2) for most PPIs is approximately 1–2 hours, but the pharmacologic effect persists due to irreversible enzyme inhibition. H2RAs are primarily renally excreted; for example, famotidine’s t_1/2 is 3–4 hours. Antacids are excreted unchanged in the feces and urine. Sucralfate is excreted in the feces with negligible systemic absorption.

Dosing Considerations

PPIs are typically dosed once daily, ideally 30–60 minutes before a meal to allow drug accumulation in the parietal cell canaliculi. The standard dose for omeprazole is 20–40 mg daily; esomeprazole is 20 mg daily. H2RAs can be dosed twice daily; for instance, famotidine 20 mg twice daily. Antacids are taken symptomatically, often after meals or at bedtime. Sucralfate is administered 4–5 times daily, 30 minutes before meals and at bedtime, as its protective effect is maximized when applied to the ulcer surface without interference from gastric acid.

Therapeutic Uses/Clinical Applications

Peptic Ulcer Disease

PPIs are first‑line therapy for erosive gastritis, duodenal ulcers, and healing of gastric ulcers. H2RAs serve as alternative therapy in mild to moderate ulcers or in patients intolerant to PPIs. Antacids provide symptomatic relief for mild dyspepsia and are often combined with acid‑suppressive agents. Sucralfate is indicated for ulcer healing, particularly when mucosal protection is desired in the presence of NSAID therapy.

Helicobacter pylori Eradication

Combination therapy involving a PPI, clarithromycin, and amoxicillin or metronidazole constitutes standard first‑line eradication regimens. The PPI enhances bacterial eradication by raising gastric pH, thereby increasing antibiotic stability and bacterial susceptibility. H2RAs can also be used in triple therapy, but PPIs provide superior eradication rates. Sucralfate is generally avoided during eradication therapy due to potential interference with antibiotic absorption.

NSAID‑Induced Gastric Protection

PPIs are routinely prescribed for patients on chronic NSAID therapy to prevent gastric ulceration and bleeding. H2RAs may be considered for patients with mild NSAID‑related gastritis. Antacids offer temporary relief but are insufficient for prophylaxis. Sucralfate is occasionally used as an adjunct in high‑risk patients, though PPIs remain the preferred choice due to superior efficacy.

Reflux‑Related Disorders

PPIs are the mainstay for gastroesophageal reflux disease (GERD), providing potent acid suppression. H2RAs are used for mild GERD or as rescue therapy. Antacids provide rapid, short‑term symptom relief. Sucralfate is not typically employed for reflux disorders.

Other Indications

PPIs are increasingly used for the management of Zollinger‑Ellison syndrome, a gastrin‑secreting tumor that produces excessive acid. H2RAs may be used in pediatric populations for ulcer prevention. Antacids are indicated for acute gastric upset, including over‑the‑counter use for heartburn. Sucralfate is employed in patients requiring mucosal protection during chemotherapy or radiation therapy involving the upper GI tract.

Adverse Effects

Common Side Effects

• Headache
• Diarrhea or constipation
• Nausea and vomiting
• Abdominal pain and bloating
• Flatulence

Serious/ Rare Adverse Reactions

PPIs can be associated with Clostridioides difficile colitis due to altered gastric pH, potentially impairing host defense. Long‑term use has been linked to hypomagnesemia, particularly with high‑dose or chronic therapy. Osteoporotic fractures may increase in patients on prolonged PPIs, especially in the elderly. H2RAs carry a risk of drug interactions through CYP450 inhibition, notably with warfarin, leading to increased anticoagulant effects. Antacids containing aluminum or magnesium can cause constipation or diarrhea, respectively. Sucralfate may cause constipation due to its viscous nature and can interfere with the absorption of concurrently administered drugs.

Black Box Warnings

PPIs possess a black box warning regarding the risk of Clostridioides difficile infection, particularly in hospitalized patients or those on prolonged therapy. H2RAs have a warning about potential drug interaction with anticoagulants, especially warfarin. Antacids are cautionary for patients with renal insufficiency due to accumulation of aluminum or magnesium salts. Sucralfate carries a warning regarding the potential to alter the absorption of other medications when administered concurrently.

Drug Interactions

Proton Pump Inhibitors

• Clopidogrel: PPIs, especially omeprazole and esomeprazole, inhibit CYP2C19, potentially reducing clopidogrel activation and antiplatelet efficacy.
• Warfarin: PPIs may potentiate warfarin anticoagulant effects by inhibiting hepatic metabolism.
• Diazepam: PPIs can increase diazepam plasma concentrations due to CYP3A4 inhibition.
• Rifampin: Rifampin induces CYP3A4, decreasing PPI concentrations.

Histamine‑2 Receptor Antagonists

• Cimetidine: Inhibits CYP450 enzymes, affecting metabolism of numerous drugs such as warfarin, phenytoin, and theophylline.
• Famotidine: Minimal CYP450 interaction but may displace other drugs from albumin binding sites.

Antacids

• Calcium‑based antacids: Reduce absorption of oral iron, levothyroxine, and certain antibiotics (e.g., tetracyclines, fluoroquinolones).
• Magnesium hydroxide: Can increase plasma magnesium, especially in renal impairment.

Sucralfate

• Interferes with absorption of drugs such as methotrexate, levothyroxine, tetracyclines, and fluoroquinolones when administered concurrently due to its strong binding to mucosal surfaces.

Special Considerations

Pregnancy and Lactation

PPIs and H2RAs are generally considered category B drugs for pregnancy, indicating no evidence of risk in humans. However, the safety of long‑term use remains under investigation. Antacids are considered safe but may contain excipients that warrant caution. Sucralfate is available in a low‑dose formulation (1 g/5 mL) for use in pregnancy, though data are limited. Lactation is not contraindicated for PPIs, H2RAs, or antacids; however, sucralfate may pass into breast milk in small amounts. Clinical judgment should guide therapy in lactating mothers.

Pediatric Considerations

PPIs are approved for children over 6 months of age for the treatment of erosive gastritis and GERD. Dosage is weight‑based, typically 1 mg/kg per day. H2RAs are also used in pediatric populations for mild ulcer disease. Antacids are often employed for symptomatic relief in children with mild dyspepsia. Sucralfate is approved for pediatric ulcer therapy, with dosing adjusted for age and weight. Monitoring for growth suppression and nutrient malabsorption is advisable with long‑term therapy.

Geriatric Considerations

Elderly patients exhibit altered pharmacokinetics, including reduced hepatic clearance and increased risk of drug interactions. PPIs may increase the risk of falls due to hypomagnesemia, and bone density loss has been associated with prolonged use. H2RAs are generally better tolerated, but cimetidine’s CYP inhibition may precipitate drug interactions. Antacids can exacerbate constipation, a common geriatric complaint. Sucralfate may cause constipation and should be used cautiously in frail elderly patients.

Renal and Hepatic Impairment

In hepatic impairment, PPIs are metabolized more slowly; dose adjustments may be required. PPIs with minimal hepatic metabolism (e.g., pantoprazole) are preferable. H2RAs such as famotidine are primarily renally cleared; dose reduction is warranted in chronic kidney disease. Antacids containing magnesium or aluminum should be avoided in advanced renal failure due to accumulation. Sucralfate is not absorbed and is safe in hepatic impairment, but caution is advised in renal dysfunction due to potential fecal excretion overload.

Summary/Key Points

• PPIs provide the most potent and durable acid suppression, making them first‑line agents for peptic ulcer disease and NSAID‑related ulcer prophylaxis.
• H2RAs offer effective, reversible acid suppression suitable for mild ulcer disease and as rescue therapy; their CYP inhibition can lead to significant drug interactions.
• Antacids deliver rapid, transient symptom relief but lack ulcer‑healing properties; they may interfere with absorption of certain medications.
• Sucralfate acts as a mucosal protective barrier, beneficial in ulcer healing, particularly in the presence of NSAIDs or chemotherapy.
• Long‑term PPI therapy is associated with hypomagnesemia, bone density loss, and increased risk of opportunistic infections; monitoring and dose optimization are essential.
• Drug interactions are most pronounced with PPIs (clopidogrel, warfarin) and cimetidine (CYP inhibition); careful medication reconciliation is advisable.
• Special populations (pregnancy, pediatrics, geriatrics, renal/hepatic impairment) require dose adjustments and vigilant monitoring for adverse effects.

Consideration of pharmacologic principles, patient characteristics, and clinical context is paramount when selecting agents for peptic ulcer therapy. The therapeutic goal remains the promotion of ulcer healing while minimizing adverse outcomes and drug interactions.

References

1. Katzung BG, Vanderah TW. Basic & Clinical Pharmacology. 15th ed. New York: McGraw-Hill Education; 2021.
2. Golan DE, Armstrong EJ, Armstrong AW. Principles of Pharmacology: The Pathophysiologic Basis of Drug Therapy. 4th ed. Philadelphia: Wolters Kluwer; 2017.
3. Rang HP, Ritter JM, Flower RJ, Henderson G. Rang & Dale's Pharmacology. 9th ed. Edinburgh: Elsevier; 2020.
4. Brunton LL, Hilal-Dandan R, Knollmann BC. Goodman & Gilman's The Pharmacological Basis of Therapeutics. 14th ed. New York: McGraw-Hill Education; 2023.
5. Trevor AJ, Katzung BG, Kruidering-Hall M. Katzung & Trevor's Pharmacology: Examination & Board Review. 13th ed. New York: McGraw-Hill Education; 2022.
6. Whalen K, Finkel R, Panavelil TA. Lippincott Illustrated Reviews: Pharmacology. 7th ed. Philadelphia: Wolters Kluwer; 2019.
7. Golan DE, Armstrong EJ, Armstrong AW. Principles of Pharmacology: The Pathophysiologic Basis of Drug Therapy. 4th ed. Philadelphia: Wolters Kluwer; 2017.
8. Katzung BG, Vanderah TW. Basic & Clinical Pharmacology. 15th ed. New York: McGraw-Hill Education; 2021.