GI Medications Lecture Notes

GI Medications

Acid-Controlling Drugs
Chapter 50
Pathophysiology of Acid-Related Disorders

  • Hydrochloric Acid (HCl): A strong acid produced by the stomach, essential for digestion.

  • Bicarbonate: A base produced by the pancreas that neutralizes stomach acid.

  • Pepsinogen: An inactive enzyme that converts to pepsin in the presence of HCl, aiding protein digestion.

  • Intrinsic Factor: A glycoprotein essential for vitamin B12 absorption in the intestines.

  • Mucus: A protective secretion that coats the stomach lining, preventing damage from acid.

  • Prostaglandins: Hormone-like substances that protect the stomach lining and stimulate mucus/bicarbonate secretion.

Acid-Related Diseases

  • Gastroesophageal Reflux Disease (GERD): A chronic condition where stomach acid flows back into the esophagus.

  • Peptic Ulcer Disease (PUD): Sores developed on the lining of the stomach, small intestine, or large intestine.

  • Helicobacter pylori (H. pylori): A bacterium often responsible for peptic ulcers.

  • Stress-Related Mucosal Damage: Injury to the gastric mucosa due to stress often related to critical illness.

Antacids

  • Definition: Basic compounds used to neutralize stomach acid.

  • Composition: Salts of aluminum, magnesium, calcium, and/or sodium.

  • Calcium Antacids: May lead to kidney stones and increased gastric acid secretion.

  • Magnesium-Based Antacids: Should be avoided in patients with renal failure.

  • Sodium Bicarbonate: Highly soluble with a quick onset, but has a short duration of action.

Mechanism of Action of Antacids

  • Action: Neutralize acid secretions; do not prevent overproduction of acid.

  • Stimulation of Secretions:
      - Mucus: Creates a protective barrier against HCl.
      - Bicarbonate: Buffers the acidic properties of HCl.
      - Prostaglandins: Prevent the activation of the proton pump, contributing to gastric protection.

Indications for Antacids

  • Uses: Acute relief of symptoms linked to peptic ulcers, gastritis, gastric hyperacidity, and heartburn.

Contraindications for Antacids

  • Conditions:
      - Severe renal failure or electrolyte disturbances (risk of toxic accumulation).
      - Gastrointestinal (GI) obstruction (potential for laxative effects being dangerous).

Types of Antacids

  • Aluminum Salts: May cause constipation.

  • Magnesium Salts: Can lead to diarrhea; avoid in renal failure.

  • Calcium Salts: Linked to kidney stones and may cause rebound hyperacidity.

  • Sodium Bicarbonate: Risk of belching/gas production, often combined with simethicone.

Adverse Effects of Antacids

  • General: Minimal adverse effects reliant on the compound used; overuse can lead to metabolic alkalosis.

  • Specific Effects:
      - Aluminum/Calcium: Constipation.
      - Magnesium: Diarrhea.
      - Calcium: Kidney stones, rebound hyperacidity.
      - Calcium Carbonate: Gas and belching.

Drug Interactions of Antacids

  • Adsorption: Other drugs may adsorb to antacids reducing their effectiveness.

  • Chelation: Interaction can lead to reduced absorption of certain medications.

  • Increased pH: Alters the absorption of other drugs due to elevated stomach pH.

Histamine 2 (H2) Receptor Antagonists

  • Examples: Cimetidine (Tagamet), Famotidine (Pepcid), Ranitidine (Zantac), Nizatidine (Axid).

Mechanism of Action of H2 Antagonists

  • Function: Competes to block the H2 receptor on acid-secreting parietal cells.

  • Outcome: Reduces hydrogen ion (H+) secretion, increasing pH of stomach contents.

Indications for H2 Antagonists

  • Conditions Treated:
      - GERD
      - Peptic Ulcer Disease (PUD)
      - Erosive esophagitis
      - Adjunct therapy for upper GI bleeding.

Adverse Effects of H2 Antagonists

  • Common effects: Confusion and disorientation in elderly patients.

  • Specific Issues:
      - Cimetidine: Can lead to impotence and gynecomastia.
      - Famotidine: Associated with thrombocytopenia.

Drug Interactions of H2 Antagonists

  • Inhibition: May inhibit absorption of drugs needing an acidic environment.

  • Cimetidine: Interferes with the P-450 enzyme system, increasing some drug levels.

  • Smoking: Decreases effectiveness of H2 blockers.

Proton Pump Inhibitors (PPIs)

  • Process: Parietal cells release positive hydrogen ions during HCl production via the proton pump.

  • Examples: Lansoprazole (Prevacid), Omeprazole (Prilosec), Rabeprazole (AcipHex), Pantoprazole (Protonix), Esomeprazole (Nexium).

Indications for Proton Pump Inhibitors

  • Uses:
      - GERD
      - Erosive esophagitis
      - Short-term treatment of active duodenal and benign gastric ulcers.
      - NSAID-induced ulcers.
      - Stress ulcer prophylaxis.
      - Treatment of H. pylori-induced ulcers.

Adverse Effects of Proton Pump Inhibitors

  • Potential Issues:
      - Increased risk of Clostridium difficile infections.
      - Osteoporosis and elevated fracture risk in long-term users.
      - Risk of pneumonia.
      - Magnesium depletion.
      - Possible links to dementia and lupus erythematosus.

Drug Interactions of Proton Pump Inhibitors

  • Increased Serum Levels: For diazepam and phenytoin.

  • Warfarin: Increased risk of bleeding.

  • Absorption Issues: Affects absorption of ketoconazole, ampicillin, iron salts, digoxin.

  • Clopidogrel: Interaction may decrease its effectiveness due to altered metabolism.

  • Sucralfate: May delay absorption of PPIs.

  • Food Impact: May decrease the absorption of PPIs.

Sucralfate (Carafate)

  • Description: Mucosal protectant drug used for stress ulcers and PUD.

  • Mechanism: Binds to the base of ulcers/erosions, forming a protective barrier against pepsin.

Misoprostol (Cytotec)

  • Type: Prostaglandin E analogue with cytoprotective activity.

  • Function: Protects gastric mucosa by enhancing local mucus/bicarbonate production; promotes regeneration of local cells and maintains mucosal blood flow.

Antiflatulents

  • Purpose: Used to relieve painful symptoms related to gas.

  • Mechanism: Binds or alters intestinal gas; often included in antacid combinations.

  • Example: Simethicone.

Nursing Implications for Antacids

  • Cautions: Patients with heart failure (HF) or hypertension should limit sodium intake. Medications should be administered 1-2 hours after antacids.

  • Risks: Long-term use can mask underlying diseases like malignancies or bleeding ulcers.

Nursing Implications for H2 Antagonists

  • Assessments: Evaluate for allergies and impaired renal/liver function. Be cautious with elderly or disoriented patients. Recommend taking H2 antagonists 1-2 hours before meals for maximum effectiveness.

Nursing Implications for Proton Pump Inhibitors

  • Considerations: May interact with diazepam and phenytoin, increasing serum levels. Capsule contents may be opened and mixed with apple juice without chewing or crushing.

  • Timing: Orally administered PPIs (and H2 antagonists) are most effective when taken 30-60 minutes prior to meals.

Bowel Disorder Drugs
Chapter 51
Causes of Diarrhea

  • Acute Diarrhea: Often due to:
      - Bacteria
      - Viruses
      - Drug-induced causes
      - Nutritional factors
      - Protozoa

  • Chronic Diarrhea: Associated with:
      - Tumors
      - Diabetes Mellitus
      - Addison’s Disease
      - Hyperthyroidism
      - Irritable Bowel Syndrome
      - AIDS.

Mechanism of Action of Antidiarrheals

  • Adsorbents: Coat the GI tract walls, binding to bacteria/toxins for elimination.
      - Examples: Bismuth subsalicylate (Pepto-Bismol), activated charcoal, colestipol, cholestyramine.

  • Antimotility Drugs:
      - Anticholinergics: Decrease intestinal tone and peristalsis; examples include Atropine and hyoscyamine.
      - Opiates: Reduce bowel motility/pain; examples include paregoric, opium tincture, codeine, loperamide, diphenoxylate.

  • Probiotics: Intestinal flora modifiers enhancing health.
      - Example: Lactobacillus acidophilus (Bacid).

Indications for Antidiarrheals

  • Adsorbents: Indicated for milder cases.

  • Antimotility (Anticholinergics/Opiates): Indicated for severe cases.

  • Probiotics: Used especially for antibiotic-associated diarrhea.

Adverse Effects of Antidiarrheals

  • Adsorbents: May cause increased bleeding time, constipation, confusion, tinnitus, metallic taste, dark stools.

  • Opiates: Can lead to drowsiness, dizziness, nausea, vomiting, constipation, respiratory depression.

  • Anticholinergics: May cause urinary retention, impotence, confusion, dry skin, blurred vision, hypotension.

Interactions of Antidiarrheals

  • General: Adsorbents decrease the absorption of digoxin, quinidine, hypoglycemic drugs; increase bleeding time with anticoagulants, risk of methotrexate toxicity.

Nursing Implications for Antidiarrheals

  • Precautions: Bismuth subsalicylate is contraindicated in children/teens with chickenpox/influenza due to the risk of Reye’s syndrome. Use caution with older patients and those with bleeding disorders.

Constipation

  • Definition: Abnormally infrequent and difficult passage of feces through the lower GI tract due to various diseases or drugs.

Mechanism of Action of Laxatives

  • Bulk Forming: High fiber; absorb water to increase bulk and distend the bowel, initiating reflex bowel activity.
      - Examples: Psyllium (Metamucil), Methylcellulose (Citrucel).

  • Emollient: Stool softeners and lubricants, promoting water/fat in stools.
      - Examples: Docusate salts (Colace, Surfak), mineral oil.

  • Hyperosmotic: Increase fecal water content, promoting bowel distention.
      - Examples: Polyethylene glycol (Miralax), sorbitol, glycerin, lactulose.

  • Saline: Increase osmotic pressure, resulting in bowel distention.
      - Examples: Magnesium hydroxide (Milk of Magnesia), magnesium citrate (Citroma).

  • Stimulant: Increases peristalsis via intestinal nerve stimulation.
      - Examples: Senna (Senokot), bisacodyl (Dulcolax).

Peripherally Acting Opioid Antagonists

  • Discussion: Used in treatment of opioid-related constipation, allowing normal bowel function despite opioid use.
      - Examples: Methylnaltrexone (Relistor), Alvimopan (Entereg).

Indications for Laxatives

  • Bulk Forming: Used for acute/chronic constipation, irritable bowel syndrome, diverticulosis.

  • Emollient: Beneficial for fecal impaction, facilitating bowel movements.

  • Hyperosmotic: For chronic constipation and prep for diagnostics/surgery.

  • Saline: Also for constipation and surgical prep.

  • Stimulant: For acute constipation and diagnostic/surgical preps.

Adverse Effects of Laxatives

  • Bulk-Forming: May cause impaction above strictures, fluid disturbance, esophageal blockage.

  • Emollient: Skin rashes, decreased vitamin absorption.

  • Hyperosmotic: Abdominal bloating, rectal irritation.

  • Saline: Potential magnesium toxicity; electrolyte imbalances.

  • Stimulant: Nutrient malabsorption, gastric irritation, discolored urine.

Nursing Implications for Laxatives

  • Assessment: Check fluid and electrolytes before therapy.

  • Guidance: Advise against use if experiencing nausea/vomiting or abdominal pain. Advocacy for a high-fiber diet and fluid intake as alternatives to laxatives.

  • Long-Term Risks: Dependency can develop with prolonged laxative use, leading to decreased bowel tone.

Antiemetic and Antinausea Drugs
Chapter 52
Definitions

  • Nausea: An unpleasant sensation often preceding vomiting.

  • Emesis (Vomiting): Forcible expulsion of gastric and sometimes intestinal contents.

  • Antiemetic Drugs: Medications used to alleviate nausea and vomiting.

Vomiting Center and Chemoreceptor Trigger Zone

  • Locations: Both found in the brain, responsible for triggering the vomiting reflex when stimulated.

Types of Antiemetics and Antinausea Drugs

  • Classes:
      - Anticholinergic drugs
      - Antihistamines (H1 receptor blockers)
      - Antidopaminergic drugs
      - Neurokinin antagonists
      - Prokinetic drugs
      - Serotonin blockers
      - Tetrahydrocannabinoids

Mechanism of Action of Antiemetic Drugs

  • Anticholinergic Drugs: Block ACh receptors in the inner ear, inhibiting stimuli to the vomiting center.

  • Antihistamine Drugs: Bind to H1 receptors, preventing cholinergic stimulation and thus nausea and vomiting.

  • Antidopaminergic Drugs: Block dopamine receptors in the chemoreceptor trigger zone (CTZ).

  • Prokinetic Drugs: Enhance gastric emptying and desensitize the CTZ to GI impulses; may risk tardive dyskinesia.

  • Serotonin Blockers: Used in chemotherapy-induced nausea and vomiting via blocking serotonin receptors.

  • Tetrahydrocannabinoids: Psychoactive effects used for nausea/vomiting linked to chemotherapy or AIDS-related anorexia.

Herbal Products: Ginger

  • Used effectively for nausea/vomiting from chemotherapy, morning sickness, or motion sickness.

  • Adverse Effects: Include anorexia, nausea, vomiting, skin reactions; may increase bleeding risk with anticoagulants.

Nursing Implications

  • Warnings: Many antiemetics cause drowsiness; caution with driving or hazardous tasks.

  • Alcohol: Use with antiemetics can enhance CNS depression.

  • Chemotherapy Protocol: Administer antiemetics 30-60 minutes before chemotherapy starts for optimal effect.