Pharmacology: Gastrointestinal Medications

Pharmacology: Drugs Affecting the Gastrointestinal System

• The presentation covers medications affecting the gastrointestinal system (GIT), specifically focusing on common GIT medications, including antacids, H2 antagonists, proton pump inhibitors (PPIs), and antiemetics.
• The GIT is divided into upper and lower sections.
• Understanding drug action, indications, side effects, precautions, and nursing considerations is a focus.
• Common medical/surgical problems related to the GIT are reviewed.

Upper Gastrointestinal Medications

• Antacids are the most common upper GIT medications. They neutralize stomach acid.
• Other upper GIT medications include anticholinergics, antihistamines, and antidepressants. These sometimes treat gastric dysfunction.

Antacids

• Acid-related diseases result from imbalances in gastric glands.
• Hyperacidity is the most common imbalance.
• Peptic ulcer disease is a severe acid-related condition.
• Antacids contain aluminum hydroxide, calcium carbonate, magnesium salts, and sodium bicarbonate.
• Actions: promote gastric mucosal defense (buffer); increase gastric pH, thus increasing emptying rate; promote secretion of mucus for protection against hydrochloric acid; promote bicarbonate and prostaglandins to buffer acid and prevent proton-pump activation.
• Indications: acid-related disorders (e.g., hyperacidity, peptic ulcer, gastroesophageal reflux disease); heartburn, indigestion, nervous dyspepsia; relieving pain from non-steroidal anti-inflammatory drugs (NSAIDs)
• Examples include aluminum salts (AlternaGEL), calcium salts (Oystercal, Tums), magaldrate (Losopan, Riopan), magnesium salts (Milk of Magnesia), and sodium bicarbonate (Bell-ans).
• Side effects: constipation, phosphate depletion, fecal impaction, chalky taste/intestinal obstruction, belching, flatulence; hypercalcemia, alkalosis, gastrointestinal irritation, renal calculi; diarrhea, chalky taste, belching, elevated magnesium levels; belching, abdominal distension, systemic alkalosis, hyperventilation, hypokalemia.
• Precautions: reduce absorption of other medications, especially tetracyclines; use with caution due to potential interactions with other medications; can cause early dissolving of enteric-coated medications, causing stomach upset.
• Nursing considerations: assess allergies and pre-existing conditions (renal disease, fluid imbalance); administer 2 hours before or after other medications; ensure tablets are chewed thoroughly; administer with sufficient water (240mL or more) for optimal absorption; monitor for side effects (nausea, vomiting, abdominal pain, diarrhea, constipation); monitor for therapeutic effect; protect liquid forms from light.

H2 Antagonists

• Actions: reduce acid secretion from stimuli such as food, histamine, and caffeine; block histamine receptors in acid-producing parietal cells; decrease hydrochloric acid production.
• Indications: maintenance treatment of gastric/duodenal ulcers, dyspepsia, gastroesophageal reflux disease, upper GIT bleeding.
• Examples: ranitidine, famotidine, cimetidine.
• Side effects: headache, constipation, nausea, diarrhea, rash, dizziness, flatulence, musculoskeletal pain, depending on medication chosen.
• Precautions: avoid alcohol, spicy foods, smoking; avoid taking with antacids (separate by at least two hours); dispersible tablets should be dissolved in water before swallowing; ensure IV solutions are administered slowly ;protect tablets from light.
• Nursing considerations: assess allergies; monitor for medication interactions, especially taking with antacids (separate time by 2 hours at least); administer with water; ensure proper administration; protect tablets from light.

Proton Pump Inhibitors (PPIs)

• Actions: reduce gastric acid production by blocking the proton pump in parietal cells; inhibit basal and stimulated gastric acid secretion.
• Indications: treatment of duodenal ulcer, benign gastric acid reflux, esophagitis, gastrinoma, Helicobacter pylori-induced ulcers; maintenance therapy for gastroesophageal reflux disease.
• Examples: omeprazole, pantoprazole, esomeprazole.
• Side effects: rash, urticaria, alopecia, arthralgia, muscle weakness, headache, dizziness, insomnia, abdominal pain, diarrhea, depending on chosen medication.
• Precautions: advise patient not to drive or operate machinery if dizziness occurs.
• Nursing considerations: capsules, tablets, and pellets should be swallowed whole with water; powder should be protected from light; monitor for side effects.

Anti-Emetics

• Nausea and vomiting are often responses to remove harmful substances from the body (before absorption).
• Actions: act on various body systems (GIT, semi-circular canals, vomiting centre in the brain); often prokinetic agents; stimulate peristalsis to increase gastric emptying; reduce impulses to vomiting centre.
• Indications: relieve nausea/vomiting caused by cytotoxic chemotherapy, gastroesophageal reflux, vertigo, post-operative period.
• Examples: dolasetron, ondansetron, domperidone, prochlorperazine, metoclopramide.
• Side effects: depends on medication; can include oculogyric crisis, headache, dizziness, drowsiness, diarrhoea, constipation, pain, pruritis, insomnia, gastroesophageal reflux, hyperkalemia, extrapyramidal reactions.
• Precautions: avoid alcohol, spicy foods, smoking, caffeine; hypotension may occur, especially with the elderly; patient should be warned not to drive/operate machinery due to possible drowsiness.
• Nursing considerations: do not administer until underlying cause determined; monitor vitals; metoclopramide is compatible with morphine/pethidine; protect medication from light; slow administration of IV; avoid co-administering with antacids (separate by 2 hours).

Lower Gastrointestinal Medications

• Medications used to treat the lower GIT are focused on conditions such as diarrhea, constipation, and impaired digestion.
• These medications include antidiarrheals (adsorbents, anticholinergics, intestinal flora modifiers, opiates), and laxatives (bulk-forming, stimulants, saline or osmotic, emollients).

Antidiarrheals

• Actions vary depending on the type (e.g., adsorbents coat the intestinal mucosa, anticholinergics decrease peristalsis).
• Indications: diarrhea relief, prevention of fluid/electrolyte loss, chronic diarrhea due to conditions such as tumors or irritable bowel syndrome.
• Examples: loperamide (adsorbent), hyoscine N-butylbromide (anticholinergic), Lactobacillus acidophilus (flora modifier), codeine phosphate (opiate).
• Precautions: avoid if pregnant or breastfeeding.
• Nursing considerations: assess individual history (bowel habits, dietary changes, allergies); use adsorbents cautiously with patients with bleeding disorders; avoid administering anticholinergics to patients with glaucoma, urinary retention, or cardiac problems; monitor fluid balance/hydration status; monitor symptoms.

Laxatives

• Types include bulk forming, stimulants, saline/osmotic, emollients.
  • Bulk forming actions/indications: increase volume of feces by absorbing water; used in constipation, hemorrhoids, bowel preparation, and acute diarrhea
  • Stimulants actions/indications: increase peristalsis; used in acute/chronic constipation, bowel preparation
  • Saline/osmotic actions/indications: increase osmotic pressure in bowels, induce diarrhea; used in constipation, diagnostic bowel prep, parasite removal
  • Emollients actions/indications: act as stool softeners, increase water/fat in stools, lubricate stool; used for acute/chronic constipation, painful anorectal disorders.
• Examples: psyllium, sterculia, ispaghula (bulk-forming); bisacodyl, glycerol (stimulants); lactulose, sodium phosphate (saline/osmotic); docusate sodium, poloxamer (emollients).
• Side effects can vary based on the type of laxative and the amount taken (e.g., nausea, flatulence, abdominal cramps, constipation).
• Nursing considerations of laxatives include thorough history taking from patient, assessing fluid/electrolyte balance before initiating therapy; patients taking laxatives should be encouraged to consume plenty of water, especially with bulk forming.