GI Drugs Flashcards
- H2 receptor antagonist: blocks H2 activation of proton pump
- Proton pump inhibitor: proton pump on parietal cells use ATP to pump H+ out in exchange for K+ in
- Antacids
- Mucosal protective agents
Sites of action of drugs used for GI diseases
- H2 receptor antagonist (directly blocks histamine-regulated acid secretion)
Mech: Blunts parietal cell acid-secretion response to acetylcholine and gastrin; up to 90% inhibition of nocturnal gastric acid secretion
Clinical use: treat and prevent peptic ulcer disease & GERD, especially for nocturnal symptoms
Ranitidine; Famotidine (but not Cimetadine)
- Proton pump inhibitor
Mech: irreversible inhibition of parietal cell proton pump
ADME: Are acid labile → require enteric coating to get past stomach; metabolized by P450
Clinical use:
i. Peptic ulcer disease and GERD, especially for daytime symptoms
ii. First choice in Zollinger-Ellison Syndrome: a gastrin-secreting tumor
Adverse: Well tolerated, but nausea, dizziness and diarrhea may occur; increase incidence of pneumonia (due to decreased control of bacteria by acid)
Omeprazole
Weak bases that are poorly absorbed, and directly neutralize stomach acids
Antacids
- Diarrhea producing antacid; also a Saline Laxative
Mech: administered as hypertonic solution → osmotic pressure leads to accumulation of fluids in GI tract and stimulation of paristalsis
Clinical use:
- Cathartic dose (increased intestinal activity and water stool)
- First line treatment for Irritable Bowel Syndrome w/ predominant constipation → increases stool frequency and loosen consistency
Mg(OH)2
Clinical use: occasional heartburn (for long term use, use Ranitidine, Famotidine or Omeprazole)
ADME: Increase in urinary pH alters elimination
Adverse: can increase or decrease the absorption of many classes of drugs
Al(OH)3; CaCO3
- Mucosal protective agent
Mech: forms paste-like gel at low pH that adheres to positively charged proteins of epithelial cells and ulcer craters
Adverse: can adsorb other drugs (e.g., tetracyclin, phenytoin, digoxin); do not co-admin with antacids (b/c only works at low pH)
Sucralfate
Mucosal protective agent; active ingredient in Pepto-Bismol
Mech: binds selectively to ulcers to protect against acids and pepsin
Bismuth Subsalicylate
- Pro-kinetic agent
Mech: Enhances Ach release in myenteric plexus, increasing esophageal clearance and intestinal motility
Adverse: Parkinson-like symptoms and Tardive Dyskinesia (b/c has D2 receptor antagonist activity)
Metoclopramide
- Stimulant laxative
Mech: Increases intestinal fluid secretion → increasing number of bowel movements
Clinical use: idiopathic chronic constipation in adults (abdominal pain, bloating, straining, hard stools)
Adverse: diarrhea, abdominal pain, distention
Lubiprostone
- Anti-diarrheal agent; an opioid with low abuse potential
Mech: stimulates mu-opioid receptors, slowing intestinal transit time
Clinical use: First line for Diarrhea-predominant IBS (IBS-D)
Adverse: Constipation, toxic megacolon; avoid in ulcerative colitis or dysentery; at high doses, can cross BBB and result in CNS toxicity
Loperamide
- Anti-emetic prior to chemotherapy or surgery
Mech: Chemotrigger zone has high concentration of 5-HT3 receptors → Is a selective 5-HT3 receptor antagonist
Ondansetron
- 5-HT3 receptor antagonist
Mech: Decreased colonic motility via enteric and CNS blockade of 5-HT3 receptors
Clinical use: secondary tx (approved for women) with IBS-D
Adverse: Ischemic colitis (rare, but severe); constipation
Alosetron
- Glucocorticoid
Clinical use: treatment for active IBD
Mech: reduce inflammatory responses → reduce ulceration and initial remission
Prednisone
- Purine anti-metabolite
Clinical use: immunosuppressive for long-term treatment of IBD
Adverse: bone marrow suppression, rashes, fever, nausea
Azathioprine
