Pharmacology of GI Drugs: Gastric Acid Reducers

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Questions and Answers

Which drug class physically neutralizes gastric acid?

Potassium-competitive acid blockers

Antacids (correct)

H2 receptor antagonists

Proton pump inhibitors

What is a common adverse effect of Calcium Carbonate?

Diarrhea

Dizziness

Cramps

Flatulence (correct)

Which of the following drugs is an antacid that may induce rebound acid secretion?

Magnesium hydroxide

Sodium bicarbonate

Calcium carbonate (correct)

Aluminum hydroxide

What caution is advised when using Magnesium Hydroxide?

Renal impairment Signup and view all the answers

Which drug is combined with Aluminum Hydroxide to provide faster acid neutralization?

Magnesium hydroxide Signup and view all the answers

What is the primary therapeutic action of Proton Pump Inhibitors (PPIs)?

Reducing gastric acid secretion Signup and view all the answers

Which antacid is known for being a strong osmotic agent?

Magnesium hydroxide Signup and view all the answers

What is a potential serious effect of Aluminum Hydroxide particularly in patients with renal impairment?

Aluminum toxicity Signup and view all the answers

What is the primary mechanism of action of H2 receptor antagonists?

They compete with histamine for H2 receptor binding. Signup and view all the answers

Which adverse effect is commonly associated with the use of H2 receptor antagonists?

Headache Signup and view all the answers

What effect do antacids have on the absorption of certain medications?

Decrease absorption of iron and some antifungals. Signup and view all the answers

When should antacids be administered in relation to other medications?

2 hours before or after other medications. Signup and view all the answers

Which of the following is a known drug interaction with cimetidine?

Increased INR with warfarin. Signup and view all the answers

What percentage of acid secretion do proton pump inhibitors typically reduce?

80-95% Signup and view all the answers

What is a rare adverse effect of H2 receptor antagonists?

Thrombocytopenia Signup and view all the answers

In what condition might H2 receptor antagonists be prescribed?

Stress ulcers Signup and view all the answers

What is the mechanism of action of proton pump inhibitors (PPIs)?

Irreversibly inhibits H+/K+-ATPase by binding to sulfhydryl groups Signup and view all the answers

Which side effect is commonly associated with the use of proton pump inhibitors?

Diarrhea Signup and view all the answers

How does vonoprazan, a potassium-competitive acid blocker (PCAB), differ from PPIs?

It can be taken without regard to food Signup and view all the answers

What condition is a common indication for the use of misoprostol?

NSAID-induced ulcers Signup and view all the answers

What interaction should be closely monitored when using omeprazole?

Increased levels of warfarin Signup and view all the answers

What is a key advantage of potassium-competitive acid blockers over proton pump inhibitors?

They have rapid onset and prolonged duration of action Signup and view all the answers

Which condition is NOT typically treated with proton pump inhibitors?

Chronic hypertension Signup and view all the answers

What action do proton pump inhibitors perform to enhance gastric mucosal defense?

Inhibits gastric acid secretion Signup and view all the answers

Signup and view all the answers

Study Notes

Pharmacology of GI Drugs 1: Gastric Acid Reducing Drugs

This presentation covers gastric acid-reducing drugs, specifically antacids, H2 receptor antagonists (H2RAs), proton pump inhibitors (PPIs), potassium-competitive acid blockers (PCABs), and mucosal defense-enhancing drugs.
Learning Objectives: Compare and contrast the therapeutic and adverse effects of different drug classes, identify pharmacokinetic characteristics, and recognize common drug interactions, precautions, and contraindications.

Antacids

Mechanism of Action (MOA): Physically neutralize gastric acid.
Agents: Calcium carbonate, magnesium hydroxide, aluminum hydroxide, and sodium bicarbonate (not recommended).

Calcium Carbonate

Brand Names: Tums®, Rolaids®.
Neutralizing Ability: Moderate.
Adverse Effects: Belching, flatulence, nausea, constipation, and potential for rebound acid secretion. Short-term hypercalcemia is possible due to absorption. Should be used with caution in renal disease or kidney stones.
Dosage: Take 1 hour after meals and at bedtime.

Magnesium Hydroxide

Neutralizing Ability: Rapid.
Adverse Effects: Antacid-laxative effect when used alone (Phillips® Milk of Magnesia). Combining with aluminum hydroxide reduces the laxative properties (Maalox®, Mylanta®.) May cause chelation of other GI tract drugs. Cautious use in renal impairment and geriatric patients.
Use with Caution: Renal impairment, geriatric patients

Aluminum Hydroxide

Neutralization: Takes time/slow.
Treatment for: Hyperphosphatemia
Side Effects: May cause constipation. Caution in renal impairment. Aluminum toxicity, encephalopathy, and chelation of other drugs. Increased bone resorption and osteoporosis with prolonged use.
Brand name: Amphojel®

Antacids- Considerations For Use

Dosage: Best results 1 hour after meals and at bedtime. Liquids preferred over tablets. Chew tablets thoroughly and take with water.
Drug Interactions: Antacids may cause chelation of some drugs (e.g., quinolones, tetracyclines, levothyroxine). Administer antacids 2 hours before or after other medications. Levothyroxine should be administered at least 4 hours before or after antacids. May affect absorption of iron, or certain HIV medications, and some azole antifungals.

H2 Receptor Antagonists (H2RAs)

Mechanism of Action (MOA): Competitive antagonists of histamine at H2 receptors on parietal cells, inhibiting acid secretion.
Available Agents: Cimetidine, famotidine, and nizatidine.
Adverse Effects (Common): Diarrhea, constipation, drowsiness, headache, dizziness.
Adverse Effects (Rare): Thrombocytopenia, vitamin B12 deficiency, confusion, delirium, hallucinations (CNS effects), and gynecomastia (with cimetidine); IV formulations can be used for elderly patients who need quicker onset.
Drug Interactions: Some H2RAs, especially cimetidine, inhibit cytochrome P450 enzymes, potentially impacting metabolism of other drugs (e.g., warfarin). Eletriptan should not be administered within 72 hours of cimetidine. Avoiding concomitant use of phenytoin with some H2RAs due to toxicity concerns. Drugs affected by increased gastric pH.

Proton Pump Inhibitors (PPIs)

Mechanism of Action (MOA): Irreversibly inhibit gastric H+/K+-ATPase (proton pump), reducing acid secretion.
Prodrugs: Require acid activation.
Agents: Dexlansoprazole, esomeprazole, lansoprazole, omeprazole, pantoprazole, rabeprazole.
Adverse Effects: Diarrhea, headache, nausea, constipation, flatulence, abdominal pain.
Drug Interactions: Omeprazole, and esomeprazole inhibit the metabolism of certain drugs through CYP inhibition, including clopidogrel, ketoconazole, warfarin, and diazepam.

Potassium-Competitive Acid Blockers (PCABs)

Mechanism of Action: Inhibits H+/K+-ATPase in a potassium-dependent manner.
Agent: Vonoprazan
Adverse Effects: Nasopharyngitis, diarrhea, constipation, flatulence, abdominal pain, dyspepsia, headache.
Drug Interactions: CYP3A4 inducers and drugs with pH dependent absorption.

Misoprostol (Cytotec®)

Mechanism of Action: Prostaglandin E1 analog, acting on gastric mucosa to increase mucus and bicarbonate production, and reduce acid secretion.
Indication: Usually used to prevent NSAID-induced ulcers.
Adverse Effects: Multiple daily doses, diarrhea, abdominal cramps, potential exacerbation of inflammatory bowel disease. Must be used with caution, due to pregnancy contraindications.

Sucralfate (Carafate®)

Mechanism of Action: Forms a protective coating over ulcer areas.
Adverse Effects: Constipation.
Avoid in: Severe renal impairment.
Drug-Interactions: Inhibits absorption of phenytoin, digoxin, fluoroquinolones, and ketoconazole.

Bismuth Subsalicylate

Mechanism of Action: Direct mucosal protective effect and antimicrobial action against H. pylori.
Adverse Effects: Black stools, discoloration of oral cavity and tongue, constipation.
Cautious Use: Salicylate allergy, children under 12(risk of Reye's syndrome), increases bleeding risk

Principles of Therapy

Basis of Therapy: Neutralize excess acid, reduce gastric acid secretion, enhance gastric mucous defense. Different disease states (GERD, PUD, stress ulcers, Zollinger-Ellison syndrome) drive the need for different therapies.

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Description

This quiz explores the pharmacology of gastric acid-reducing drugs, including antacids, H2 receptor antagonists, proton pump inhibitors, and more. You'll learn about their therapeutic effects, adverse reactions, and pharmacokinetic characteristics. Test your knowledge on the mechanisms of these drugs and their impact on gastrointestinal health.