Hesi Gastrointestinal System

Local GI Reflexes

  • Local reflexes are confined to the gut wall and intestinal wall as part of enteric nervous system activity.
  • Gastroenteric reflex: stimuli in the stomach prepare for food in the GI tract.
  • Gastrocolic reflex: stimulation of the stomach increases activity in the colon.
  • Duodenal-colic reflex: stretch in the duodenum stimulates colon activity and mass movement.
  • Other reflexes exist but are not detailed here.

Central GI Reflexes

  • Swallowing: triggered by a food bolus in the back of the throat.
  • Vomiting: controlled by two centers in the medulla.
    • Primitive center: can induce projectile vomiting (e.g., in children or brain injury).
    • Mature center: Chemoreceptor Trigger Zone (CTZ).

Chapter 57: Drugs Affecting Gastrointestinal Secretions

Histamine-2 Antagonists (H2 antagonists)

  • Drugs: ranitidine (Zantac), famotidine (Pepcid), cimetidine (Tagamet), nizatidine (Axid) – the class name ends with “-tidine”.
  • Mechanism: suppress release of gastrin from parietal cells by blocking the H2 receptor; decreased gastrin → decreased hydrochloric acid production.
  • Note: H2 receptors are also found in the heart; theoretical risk for arrhythmias.
  • Uses:
    • Short-term treatment of active duodenal or gastric ulcers
    • Treatment of hypersecretion of hydrochloric acid
    • Prophylaxis of stress-induced ulcers
    • Treatment of GERD
    • Relief of heartburn, acid indigestion, and sour stomach
  • Pharmacokinetics: all are metabolized by the liver except nizatidine (Axid).
  • Special combos: Famotidine in combination with an NSAID (RelEtis/RelVis term in text) to reduce NSAID-induced GI ulcers (commonly referred to in practice as a combination product; text notes people often mislabel this as an “antacid”).
  • Important recall/notes:
    • Confusion in textbook terminology: RelEtis may be misnamed; focus on classification, not generic mislabeling.
    • Textbook page note: p. 999 contains a confusing section.
Recalls and NDMA risk
  • Current recalls: ranitidine recalled; nizatidine voluntary recall.
  • Reason: Increased levels of NDMA (N-Nitrosodimethylamine), a probable human carcinogen, associated with storage over time.
  • Impact: Not all products tested show increased NDMA; risk outweighed benefit leading to recall.
  • Market impact: Increased use of famotidine (Pepcid) causing supply shortages.
Adverse effects
  • Gastrointestinal upset
  • Central nervous system effects: dizziness, headache, confusion (due to CNS H2 receptors)
  • Cardiovascular: arrhythmias and hypotension (due to H2 receptors in heart)
  • Endocrine/sexual effects: gynecomastia, impotence

Antacids

  • Common agents: calcium carbonate (Tums, Oystercal), sodium bicarbonate (baking soda), magnesium salts (Milk of Mag), aluminum salts (Amphojel), combinations (e.g., Maalox – calcium and aluminum).
  • Mechanism: neutralize stomach acid.
  • Individual agent caveats:
    • Sodium bicarbonate: risk of electrolyte imbalances.
    • Calcium carbonate (Tums): constipation and acid rebound.
    • Magnesium salts (Milk of Mag): diarrhea; also used as laxative.
    • Aluminum salts (Amphojel): less likely to cause acid rebound; weaker at neutralizing acid.
  • Adverse effects: relate to acid-base and electrolyte imbalances; acid rebound can occur when the stomach compensates by producing more acid after neutralization.
  • Drug interactions: antacids can alter absorption of other medications and create an alkaline environment that impairs absorption of certain drugs; recommendation to separate other drugs by at least 2 hours.

Proton Pump Inhibitors (PPIs)

  • Drugs: omeprazole (Prilosec), esomeprazole (Nexium), lansoprazole (Prevacid), pantoprazole (Protonix) – class name ends with “-prazole”.
  • Mechanism: inhibit the hydrogen-potassium ATPase enzyme system (H⁺/K⁺-ATPase) in the parietal cells, thereby blocking acid release into the stomach lumen.
  • Use pattern: generally short-term treatment, but can be long-term if needed.
  • Uses:
    • Duodenal ulcers
    • GERD
    • Erosive esophagitis
    • Benign gastric ulcers
    • Helicobacter pylori treatment (in combination with amoxicillin and clarithromycin)
  • Pediatric note: lansoprazole is approved for children under 18; others used off-label in pediatrics.
  • Adverse effects: related to reduced acidity; potential changes to gastric flora that may increase cancer risk with long-term altered microbiota..
  • Dosing/administration:
    • Generally short-term use of 2–4 weeks; some patients require longer therapy.
    • Teach patients to take before a meal; do not crush, chew, or open capsules.
    • Follow-up if symptoms persist after 4–8 weeks.
  • Special relevance: often prescribed to patients who routinely take NSAIDs.

Gastrointestinal Protectant

  • Sucralfate (Carafate)
  • Mechanism: coats injured gastric mucosa, protecting it from acids and bile; creates a protective barrier to allow healing.
  • Contraindications/ cautions:
    • Renal failure or dialysis patients due to aluminum buildup.
    • Caution when combined with aluminum salts due to potential aluminum toxicity.
  • Administration: empty stomach; take 1 hour before or 2 hours after meals.

Prostaglandins

  • Misoprostol (Cytotec) – prostaglandin E analogue
  • Mechanism: protects stomach lining by inhibiting gastric acid secretion and increasing bicarbonate and mucus production.
  • Primary use: prevent NSAID-induced gastric ulcers.
  • Important safety measures: can cause uterine contractions; ensure a negative serum pregnancy test within 2 weeks of starting therapy; begin therapy on the 2nd or 3rd day of the menstrual cycle; use barrier contraception during treatment.

Digestive Enzymes

  • Forms: saliva substitutes (for dry mouth or swallowing difficulties) and pancreatic enzyme replacements (ptyal substitutes cover bolus formation and lubrication).
  • Saliva substitutes examples: MouthKote, Salivart; role: thickening agent to aid swallowing.
  • Pancrelipase (Creon, Pancrease): replace enzymes needed to digest fats, proteins, and carbohydrates.
  • Indications: pancreatic insufficiency (e.g., cystic fibrosis, chronic ductal obstruction), radiation/chemo-induced damage, etc.

Chapter 58: Drugs Affecting Gastrointestinal Motility

Laxatives

  • Indications: short-term relief of constipation; help patients avoid straining (e.g., after surgery or in patients with cardiac conditions);
    • Prep for bowel diagnostics
    • Remove poisons from GI tract
  • Types:
    • Chemical stimulants
    • Bulk stimulants
    • Lubricants
Chemical stimulants
  • Examples: Bisacodyl (Dulcolax), castor oil, senna
  • Mechanism: stimulate the nerve plexus, increasing movement and local reflex activity; act from the small intestine through the entire GI tract when given PO.
  • Considerations: frequent use can lead to laxative dependence; can cause constipation or impaction if overused.
  • Specific notes: Bisacodyl is milder than castor oil; avoid taking with other meds within at least 30 minutes to prevent premature removal before absorption.
Bulk stimulants
  • Examples: polyethylene glycol (MiraLax), magnesium hydroxide (Milk of Mag), polycarbophil (FiberCon), psyllium (Metamucil), polyethylene glycol-electrolyte solution (GoLYTELY), lactulose (Constilac).
  • Mechanism: act by increasing stool bulk and water content, stretching the colonic wall to trigger local reflexes.
  • Uses: constipation relief; bowel prep for diagnostics; similar adverse effects and precautions as chemical stimulants; dosing-dependent.
Lubricants (stool softeners)
  • Examples: docusate (Colace), glycerin, mineral oil
  • Mechanism: soften stool, facilitate defecation without stimulating movement.
  • Indications: post-surgical patients, patients with hemorrhoids.
  • Cautions: prolonged use can interfere with absorption of fat-soluble vitamins A, D, E, and K.

General teaching for all laxatives

  • Temporary use; maintain adequate fluid intake (increased fluids especially with bulk laxatives).
  • Encourage patients to keep enemas and suppositories in place as long as possible when using.
  • Do not administer laxatives in the presence of acute abdominal pain, nausea, or vomiting.
  • Provide comfort and safety measures, particularly in elderly patients or those with certain medical conditions.

Gastrointestinal Stimulants

  • Metoclopramide (Reglan)
  • Mechanism: stimulates parasympathetic activity in the GI tract; increases GI secretions and motility.
  • Indication: used when more rapid movement of GI contents is desirable.
  • Adverse effects: N/V, diarrhea, intestinal spasm, cramping; parasympathetic stimulation can cause decreased BP, decreased HR, etc.
  • Teaching: usually given 15–30 minutes before a meal and at bedtime; monitor BP, especially if given IV.

Antidiarrheals

  • Subsalicylate (Pepto-Bismol) and loperamide (Imodium)
  • Mechanisms:
    • Pepto-Bismol acts on the lining of the GI tract to inhibit local reflexes.
    • Imodium acts on the GI tract muscles to slow activity.
  • Cautions/contraindications: history of GI obstruction or acute abdominal conditions; diarrhea due to poisoning; hepatic impairment.
  • Adverse effects: constipation, N/V, abdominal pain; fatigue, weakness, dizziness

Traveler’s Diarrhea

  • Rifaximin
  • Use: antibiotic specifically for treatment of traveler’s diarrhea; active against E. coli (the most common cause).
  • Regimen: started once symptoms occur; typically three times daily (t.i.d.) for 3 days.
  • Prevention: best intervention is prevention; recommendations include:
    • Drink only bottled water
    • Avoid fresh fruits/vegetables washed in local water unless peeled
    • Avoid ice cubes in drinks
    • Avoid undercooked or rare foods
    • Be cautious when brushing teeth with local water; use bottled water when possible

Irritable Bowel Syndrome (IBS) Drugs

  • Symptoms: abdominal distress, diarrhea or constipation, bloating, nausea, flatulence, HA, fatigue, depression, anxiety.
  • No known single cause; possibly stress-related.
  • Lubiprostone: chloride-channel activator that increases chloride-rich intestinal fluid production (does not change Na or K), increasing fluid -> increased motility; used for IBS-C or chronic constipation.
  • Alosetron: serotonin 5-HT antagonist; decreases perception of gastric pain and decreases GI motility; was removed from the market due to ischemic bowel risk, then re-released with Black Box Warning; requires patient-physician agreement; only approved for women; used for IBS-D.

Chapter 59: Antiemetic Agents

Emetics (inducing vomiting)

  • Ipecac syrup was historically used for poisoning at home but is no longer recommended.
  • Guidelines emphasize poison safety: keep poisons out of reach, childproof caps, keep substances in original containers, dispose of unused medications, do not refer to meds as candy, and post Poison Control number.
  • Pts should dispose of any ipecac syrup they may still have.

Antiemetic Agents (overview)

  • Goal: reduce hyperactivity of vomiting reflex via two mechanisms:
    • Local (peripheral): decrease response to stimuli reaching the medulla
    • Examples: antacids, local anesthetics, adsorbents, GI protectants, anti-distention drugs
    • Central: block CTZ in the medulla
  • Groups:
    • Phenothiazines
    • Nonphenothiazines
    • Serotonin (5-HT) receptor blockers
    • Substance P / neurokinin 1 (NK1) receptor antagonists
    • Miscellaneous agents
Phenothiazines
  • Example: prochlorperazine
  • Mechanism: centrally acting antiemetic; alters response to CTZ stimulation in the medulla.
  • Adverse effects: pink-to-brown urine discoloration, photosensitivity (use sunscreen), CNS effects (drowsiness, headache, weakness); concurrent CNS depressants (e.g., alcohol) should be avoided.
  • Note: also used as an antipsychotic medication.
Nonphenothiazines
  • Example: metoclopramide (Reglan)
  • Mechanism: reduces responsiveness of CTZ nerve cells to circulating emetic chemicals.
  • Role: antiemetic, often used postoperatively or with chemotherapy-induced N/V.
5-HT Receptor Blockers
  • Examples: ondansetron (Zofran), dolasetron (Anzemet)
  • Mechanism: block serotonin receptors in CTZ and locally in GI tract.
  • Uses: highly effective in cancer patients (chemo and radiation) and postoperative patients; available in PO and IV forms; side effects are generally mild.
Substance P / Neurokinin-1 (NK1) Receptor Antagonists
  • Examples: aprepitant (Emend), rolapitant (Varubi)
  • Use: in combination with dexamethasone; rolapitant used in combination with other antiemetics.
  • Nature: newer class; effective for chemotherapy-induced nausea and vomiting, including delayed N/V; acts in the CNS to block NK1 receptors; no direct effect on serotonin, dopamine, or corticosteroid receptors.
Miscellaneous antiemetics
  • Dronabinol (Marinol) and nabilone
  • Content: cannabinoids (THC) as part of antiemetic therapy; Schedule III controlled substances; approved for managing N/V in cancer chemotherapy patients who have not responded to other treatments in some jurisdictions; legal status varies.