Gastrointestinal System Pharmacology

Pharm 2: Unit 2 - Gastrointestinal System

Overview of Gastrointestinal Medications

  • Categories include:

    • Antacids

    • Proton Pump Inhibitors

    • H2 Receptor Antagonists

    • Mucosal Protectants

    • Antiemetics

    • Laxatives

    • Anti-Diarrheals

    • IBD Medications:

    • 5-Aminosalicylates

    • Immunosuppressants

Acid Reflux and GERD

  • Definition: Gastric contents flow "backwards" into esophagus due to increased pressure on the stomach against the lower esophageal sphincter.

  • Terminology:

    • Acid Reflux is also known as Heartburn.

    • GERD: GastroEsophageal Reflux Disease.

  • Common Causes in Adults:

    • Obesity

    • Certain Medications

    • Smoking

    • Alcohol Use

    • Trigger Foods

  • Common Causes in Young Children:

    • Immature Lower Esophageal Sphincter (LES)

    • Babies laying flat

  • Pregnancy can also contribute to GERD.

Complications of GERD

  • Potential Complications:

    • Ulceration/destruction of esophageal tissue.

    • Esophageal stricture due to repeated injury and scarring.

    • Barrett's Esophagus - precancerous changes in the esophagus.

    • Esophageal cancer.

    • Aspiration of gastric fluid leading to respiratory complications.

    • Dental erosion due to acidic damage.

  • Nursing Education Related to GERD:

    • STOP SMOKING!

    • Weight management strategies.

    • Dietary changes to avoid triggers.

    • Recommendation: Don’t lay flat after eating.

Antacids

  • Function: Help relieve symptoms of acid reflux/GERD by neutralizing gastric acid (HCl).

  • Characteristics:

    • Provides immediate relief.

    • Widely available, low-cost, OTC options include:

    • Aluminum Hydroxide (Amphojel)

    • Magnesium Hydroxide (MOM)

    • Calcium Carbonate (Tums)

    • Sodium Bicarbonate (Alka-Seltzer)

  • Potential Side Effects/Complications:

    • Constipation: Related to Calcium Carbonate and Aluminum Hydroxide.

    • Diarrhea: Related to Magnesium Hydroxide.

    • Electrolyte imbalances: Involves magnesium, phosphate, and calcium changes.

    • Fluid retention/Metabolic Alkalosis: Associated with sodium bicarbonate.

    • Kidney stone risk: Associated with calcium.

Antacids: Important Interactions

  • Drug Interactions: Decrease absorption of many medications.

  • Nursing Considerations:

    • Take other medications at least 1-2 hours before or after antacids.

    • Typically taken as needed when experiencing acid reflux.

    • Recommended to take before bedtime to prevent nocturnal reflux.

    • Monitoring: Bowel habits and electrolytes with excessive use.

    • Consider exploring other treatments for chronic use.

H2 Receptor Antagonists

  • Action: Block histamine H2 receptors on parietal cells of gastric lining, inhibiting gastric acid secretion.

  • Availability: Many are available OTC and are generally well tolerated.

  • Uses: Effective for GERD/heartburn, peptic ulcer disease (PUD), and erosive esophagitis.

  • Common Side Effects:

    • Headache (HA)

    • Dizziness

    • Fatigue

    • Vitamin B12 deficiency risk.

  • High Drug Interaction Risk: Particularly with cimetidine and in elderly patients.

  • Examples:

    • Ranitidine (Zantac)

    • Famotidine (Pepcid)

    • Cimetidine (Tagamet)

Receptor Differences

  • H1 Receptors: Present in smooth muscle, endothelium, and CNS.

  • H2 Receptors: Located specifically on parietal cells in the stomach.

Proton Pump Inhibitors (PPIs)

  • Function: Inhibit the proton pump of the stomach, reducing gastric acid secretion.

  • Usage: Typically requires daily administration for effectiveness; Short-term treatment for GERD, PUD, gastritis, and duodenal/esophageal ulcers; often used in hospitals due to stress responses.

  • Common PPIs:

    • Omeprazole (Prilosec)

    • Pantoprazole (Protonix)

    • Lansoprazole (Prevacid)

    • Esomeprazole (Nexium)

    • Dexlansoprazole (Dexilant)

  • Common Side Effects:

    • Nausea/Vomiting/Diarrhea/Abdominal pain.

  • Complications with Long-Term Use:

    • Rebound acid hypersecretion requiring a taper and potential antacid use upon discontinuation.

    • Osteoporosis risk due to decreased calcium absorption leading to potential fractures.

    • Increased risk for bacterial infections due to a lowered acidic environment, including risks of C. diff and pneumonia.

    • Risk of Vitamin B12 deficiency.

Interactions and Considerations for PPIs

  • Interactions/Contraindications:

    • Decrease effectiveness of many medications, notably clopidogrel (Plavix).

    • May slow metabolism of medications such as Warfarin, digoxin, and phenytoin.

    • Use cautiously in patients with osteoporosis or a history of pneumonia.

  • Nursing Considerations:

    • Do not break or crush time-release capsules.

    • Generally taken daily, in the morning, 30 minutes prior to breakfast.

    • Duration for therapy is typically 2-4 weeks for short-term use.

    • Important to take 1 hour before or after other oral medications.

    • Taper discontinuation for those on long-term therapy.

Mucosal Protectants

  • Function: Create a protective barrier layer on the gastric mucosa, increasing the viscosity and hydrophobicity of mucus, and absorb gastric acids to reduce concentration.

  • Uses:

    • Treats gastric, duodenal, and esophageal ulcers.

    • Prevents ulcers in severe dyspepsia and GERD.

    • Used for stomatitis, mucositis, esophagitis (often chemotherapy-induced), proctitis (often radiation-induced), and in skin/epithelial wounds.

  • Characteristics:

    • Stays in the gastrointestinal tract; not absorbed systemically.

    • Onset: within 1-2 hours with a duration of about 6 hours.

    • Typically administered for a course of 4-8 weeks to allow healing.

    • May prevent absorption of other medications.

  • Side Effect: Generally well tolerated, with constipation being a noted possible issue.

  • Example: Sucralfate (Carafate).

Antiemetics

  • Pharmacological Overview: Antiemetics address nausea and vomiting (n/v) triggered by stress, emotions, pain, and various sensory stimuli.

    • Higher brain areas, such as the cortex and limbic systems, help detect toxins and disturbances in the bloodstream.

    • Signals can originate from the vestibular system, via the vestibulocochlear nerve (for motion sickness), and from irritation/distension of the stomach/intestines through the vagus nerve.

Antiemetic Classes and Mechanisms

  • Anticholinergics: Block muscarinic M1 receptors to reduce nausea and vomiting signals.

  • Antihistamines: Block H1 receptors to decrease signals from the vestibular system.

    • Examples include: Meclizine (Antivert, Dramamine), Diphenhydramine (Benadryl).

  • 5-HT3 Antagonists: Block serotonin receptors in the gut and chemoreceptor trigger zone (CTZ).

    • Example: Ondansetron (Zofran).

  • Dopamine Antagonists: Block dopamine receptors in the gut and CTZ (e.g., Chlorpromazine, Haloperidol).

  • Benzodiazepines: Activate inhibitory GABA receptors, creating anxiety-reducing effects.

    • Examples: Lorazepam (Ativan), Diazepam (Valium).

  • Cannabinoids: Activate CNS cannabinoid receptors, having an inhibitory effect on vomiting.

Common Antiemetics and Their Uses

  • H1 Receptor Antagonists (Antihistamines):

    • Uses: Motion sickness, vertigo, postoperative n/v, morning sickness (off-label).

    • Common Side Effects: Sedation, dry mouth, blurred vision, dizziness (especially in older adults), hypotension.

  • M1 Receptor Antagonists (Anticholinergics):

    • Example: Scopolamine Patch (Transderm Scop).

    • Use for motion sickness, pre-operative drying secretions, etc.

    • Common Side Effects: Sedation, dry mouth, urinary retention.

  • 5-HT3 Antagonists:

    • Prevents signals to the vomiting center; common use in chemotherapy-induced n/v, etc.

    • Side Effects: Headaches, dizziness, rare QT prolongation.

  • Dopamine Antagonists:

    • Effects include sedation; can produce extrapyramidal symptoms (EPS).

    • Commonly used for various gastrointestinal disorders, especially related to nausea/vomiting.

Nursing Considerations

  • General Assessment:

    • Identify underlying causes of n/v, signs of dehydration (e.g., tachycardia, skin turgor).

    • Monitor hydration and patient characteristics before medication administration.

  • Non-Pharmacological Interventions:

    • Small sips of water, bland foods, smaller meals to reduce strong odors.

  • Evaluation:

    • Look for improvement, monitoring side effects, including potential EPS and hydration status.

Constipation

  • Definition: Characterized by fewer than 3 bowel movements (BM) per week, with hard, lumpy stools and straining during defecation.

  • Common Causes:

    • Poor diet, limited physical activity, dehydration, various diseases, medications (especially opiates), pregnancy, and learned behaviors regarding bowel urges.

  • Non-Pharmacological Interventions:

    • Increase fluid intake and dietary fiber, engaging in more physical activity, and regular bowel training routines.

Laxatives

  • Types:

    • Fiber Supplements: (e.g., Metamucil, Benefiber) to add bulk to stool.

    • Stool Softeners (Emollients): (e.g., Docusate sodium) to provide moisture to the stool.

    • Osmotics: (e.g., Miralax, Lactulose) to increase osmotic pressure in the bowel.

    • Stimulants: (e.g., Bisacodyl, Senna) to stimulate peristalsis.

    • Lubricants: (e.g., Mineral Oil, Castor Oil) help lubricate stool.

    • Enemas: Different types based on composition (e.g., saline, glycerin).

Considerations Regarding Laxatives

  • Use Caution: Overuse may weaken normal bowel response, leading to dependence, bowel obstructions, or perforations.

Anti-Diarrheals

  • Types:

    • Anti-Motility Agents: (e.g., Loperamide, Codeine) which slow peristalsis and allow for more water reabsorption.

    • Anti-Cholinergics: (e.g., Scopolamine) which reduce spasms in the GI tract.

    • Antisecretory/Anti-absorbent: (e.g., Bismuth subsalicylate) to coat the GI tract's lining and prevent fluid entry.

  • Caution: Antidiarrheals may mask underlying causes of diarrhea and potentially lead to a vicious cycle.

Inflammatory Bowel Disease (IBD)

  • Types of IBD:

    • Ulcerative Colitis: Inflammation localized to the large intestine/colon.

    • Crohn's Disease: Inflammation that can affect any part of the gastrointestinal tract.

Medications Used in IBD

  • 5-Aminosalicylates: (e.g., Sulfasalazine, Mesalamine) to decrease inflammation by inhibiting prostaglandin synthesis; used for the induction and maintenance of remission in mild to moderate cases.

  • Corticosteroids: Used primarily during acute flare-ups; examples: Prednisone, Budesonide; side effects include immune suppression.

  • Antibiotics: Used more frequently for Crohn's disease, examples include Ciprofloxacin and Metronidazole.

  • Immunosuppressants: (e.g., Methotrexate) used to suppress immune response after steroids to maintain remission; requires monitoring due to side effects.

  • Biologics: Advanced therapy with targeted medications such as Adalimumab (Humira) and Infliximab (Remicade); expensive and may require pre-screening for infections before initiation.

IBD Practice Questions

  • Common questions include understanding treatment mechanisms, medication purpose, and client education focusing on understanding the medications prescribed and the rationale behind their use.