Gastrointestinal Pharmacology Flashcards
Gastrointestinal Pharmacology
H2 blockers (cimetidine, ranitidine, famotidine, nizatidine)
MOA: Reversible block of histamine H2-receptors → ↓ H+ secretion by parietal cells
Use: Peptic ulcer, gastritis, mild esophageal reflux
Adverse effects: Cimetidine is potent inhibitor of cytochrome P-450; it also has antiandrogenic effects; can cross blood-brain-barrier (confusion, dizziness, headaches), and placenta. Both cimetidine and ranitidine ↓ renal excretion of creatinine.
Gastrointestinal Pharmacology
Proton pump inhibitors (omeprazole, lansoprazole, esomeprazole, pantoprazole, dexlansoprazole)
MOA: Irreversibly inhibit H+/K+ ATPase in stomach parietal cells
Use: Peptic ulcer, gastritis, esophageal reflux, Zollinger-Ellison syndrome
Adverse Effects: ↑ risk of C difficile infection, pneumonia. ↓ serum Mg2+ with long-term use
Gastrointestinal Pharmacology
Aluminum hydroxide
MOA: Can affect absorption, bioavailability, or urinary excretion of other drugs by altering gastric and urinary pH or delaying gastric emptying
Adverse Effects: Hypokalemia. Constipation or hypophosphatemia; proximal muscle weakness, osteodystrophy, seizures
Gastrointestinal Pharmacology
Calcium carbonate
MOA: Can affect absorption, bioavailability, or urinary excretion of other drugs by altering gastric and urinary pH or delaying gastric emptying
Adverse Effects: Hypokalemia. Hypercalcemia, rebound acid ↑
Gastrointestinal Pharmacology
Magnesium hydroxide
MOA: Can affect absorption, bioavailability, or urinary excretion of other drugs by altering gastric and urinary pH or delaying gastric emptying
Adverse Effects: Hypokalemia. Diarrhea, hyporeflexia, hypotension, cardiac arrest.
Gastrointestinal Pharmacology
Bismuth, sucralfate
MOA: Bind to ulcer base, providing physical protection and allowing HCO3- secretion to reestablish pH gradient in the mucous layer
Clinical Use: ↑ ulcer healing, travelers’ diarrhea
Gastrointestinal Pharmacology
Misoprostol
MOA: PGE1 analog. ↑ production and secretion of gastric mucous barriers, ↓ acid production.
Use: Prevention of NSAID-induced peptic ulcers; maintenance of PDA. Also used off-label for induction of labor ( ripens cervix)
Adverse Effects: Diarrhea. Contraindicated in women of childbearing potential
Gastrointestinal Pharmacology
Octreotide
MOA: Long-acting somatostatin analog; inhibtits secretion of various splanchnic vasodilatory hormones.
Use: Acute variceal bleeds, acromegaly, VIPoma, carcinoid tumors.
Adverse Effects: Nausea, cramps, steatorrhea. ↑ risk of cholelithiaisis due to CCK inhibition
Gastrointestinal Pharmacology
Osmotic laxatives (magnesium hydroxide, magnesium citrate, polyethylene glycol, lactulose)
MOA: Provide osmotic load to draw water into the GI lumen
Use: Constipation. Lactulose also treats hepatic encephalopathy since gut flora degrade into metabolites that promote nitrogen excretion as NH4+
Adverse Effects: Diarrhea, dehydration; may be abused by bulimics.
Gastrointestinal Pharmacology
Sulfsalazine
MOA: A combination of sulfapyridine (antibacterial) and 5-aminosalicylic acid (anti-inflammatory). Activated by colonic bacteria.
Use: Ulcerative colitis, Crohn disease (colitis component).
Adverse Effects: Malaise, nausea, sulfonamide toxicity, reversible oligospermia.
Gastrointestinal Pharmacology
Loperamide
MOA: Agonist at μ-opioid receptors; slows gut motility. Poor CNS penetration (low addictive potential)
Use: Diarrhea
Adverse Effects: Constipation, nausea
Gastrointestinal Pharmacology
Ondansetron
MOA: 5-HT3 antagonist; ↓ vagal stimulation. Powerful central-acting antiemetic.
Use: Control vomiting postoperatively and in patients undergoing cancer chemotherapy.
Adverse Effects: Headache, constipation, QT interval prolongation.
Gastrointestinal Pharmacology
Metclopramide
MOA: D2 receptor antagonist. ↑ resting tone, contractility, LES tone, motility. Does not influence colon transport time.
Use: Diabetic and postsurgery gastroparesis, antiemetic.
Adverse Effects: ↑ parkinsonian effects, tardive dyskinesia. Restlessness, drowsiness, fatigue, depression, diarrhea. Drug interaction with digoxin and diabetic agents. Contraindicated in patients with small bowel obstruction or Parkinson disease.
Gastrointestinal Pharmacology
Orlistat
MOA: Inhibits gastric and pancreatic lipase → ↓ breakdown and absorption of dietary fats.
Use: Weight loss
Adverse Effects: Steatorrhea, ↓ absorption of fat-soluble vitamins.
Gastrointestinal Pharmacology
Ursodiol (ursodeoxycholic acid)
MOA: Nontoxic bile acid. ↑ bile secretion, ↓ cholesterol secretion and reabsorption.
Use: Primary biliary cirrhosis, gallstone prevention or dissolution.
