Gastrointestinal Flashcards
What is the mechanism of action of antacids?
Antacids are weak bases that react with gastric acid (HCl) to form water and salt, reducing stomach acidity.
Which antacids are commonly used?
Aluminum hydroxide, Magnesium hydroxide, Calcium carbonate, Sodium bicarbonate.
How do antacids affect pepsin activity?
They inactivate pepsin, preventing protein breakdown, as pepsin is inactive at pH > 4.
Which antacid causes constipation?
Aluminum hydroxide causes constipation.
Which antacid causes diarrhea?
Magnesium hydroxide causes diarrhea.
How do combination products like Maalox and Mylanta affect gut motility?
They balance effects to minimize gut motility issues.
Which antacid should be avoided in renal impairment and why?
Magnesium-based antacids; risk of magnesium toxicity.
Which antacid should be avoided in congestive heart failure (CHF) and why?
Sodium bicarbonate; causes fluid retention due to high sodium.
Which antacid should be avoided in hypertension and why?
Sodium bicarbonate; increases sodium load, worsening hypertension.
Which antacid should be avoided in chronic constipation and why?
Aluminum hydroxide; can worsen constipation.
How do antacids affect tetracyclines and fluoroquinolones?
Chelation reduces antibiotic absorption.
How do antacids affect ketoconazole and iron supplements?
Reduced absorption due to increased gastric pH.
How do antacids affect levothyroxine?
Decreased efficacy; separate dosing by 4 hours.
How do antacids affect warfarin, digoxin, and phenytoin?
Reduced absorption.
What is the mechanism of action of H2 receptor antagonists?
They block H2 receptors, reducing acid secretion.
Which H2 blocker inhibits CYP450 and has drug interactions?
Cimetidine inhibits CYP450, interacting with Warfarin, Phenytoin, Clopidogrel.
Which H2 blocker is the most potent and has minimal side effects?
Famotidine is the most potent with minimal side effects.
What is the mechanism of action of proton pump inhibitors (PPIs)?
They inhibit H+/K+-ATPase in gastric parietal cells.
What are adverse effects of PPIs?
Fractures, low B12, C. difficile risk.
What is the mechanism of action of sucralfate?
Forms a protective gel over ulcers.
What is the mechanism of action of misoprostol?
Prostaglandin analog, increases mucus/bicarbonate.
What are the mechanisms of action of bismuth salts?
Antimicrobial against H. pylori, coats ulcers, reduces pepsin activity.
What are the uses of bismuth salts?
Quadruple therapy for H. pylori, prevents traveler’s diarrhea.
What are the adverse effects of bismuth salts?
Black stools/tongue, avoid in children <12 (Reye’s syndrome risk).
How does sucralfate work in ulcer treatment?
It forms a protective barrier over ulcers.
When should sucralfate be given in relation to meals?
Before meals to allow binding to ulcers before acid exposure.
Why is misoprostol contraindicated in pregnancy?
Causes uterine contractions, miscarriage.
Why are tetracyclines contraindicated in pregnancy?
Causes fetal bone/teeth discoloration.
Why are fluoroquinolones contraindicated in pregnancy?
Cartilage damage in the fetus.
What drugs are included in quadruple therapy for H. pylori?
Bismuth + PPI + Metronidazole + Tetracycline.
What drugs are included in triple therapy for H. pylori?
PPI + Amoxicillin + Clarithromycin.
What is the mechanism of action of metoclopramide?
Dopamine antagonist, increases motility.
What are the side effects of metoclopramide?
Extrapyramidal symptoms (EPS).
Why is metoclopramide contraindicated in Parkinson’s disease?
Dopamine blockade worsens motor symptoms.
What is the use and abuse potential of loperamide?
Traveler’s diarrhea; high doses can cause opioid-like effects.
What is the use and abuse potential of diphenoxylate/atropine?
Severe diarrhea; atropine prevents abuse but still possible.
What are the mechanisms of action of opioid derivatives as antidiarrheals?
Inhibit peristalsis.
What are the mechanisms of action of absorbents as antidiarrheals?
Coats intestines, antimicrobial.
What are the mechanisms of action of fluid/electrolyte modifiers as antidiarrheals?
Reduce intestinal fluid loss.
What antidiarrheals are safe for children?
Oral rehydration solutions, Loperamide (limited use).
What antidiarrheals are safe for pregnant women?
Bismuth subsalicylate (limited use), ORS.
What is the mechanism of action of stimulant laxatives?
Increase peristalsis.
What are the adverse effects of stimulant laxatives?
Cramping.
What is the mechanism of action of bulk-forming laxatives?
Absorb water.
What are the adverse effects of bulk-forming laxatives?
Bloating.
What is the mechanism of action of osmotic laxatives?
Draws water in.
What are the adverse effects of osmotic laxatives?
Diarrhea.
What is the mechanism of action of stool softeners?
Increase water penetration.
What are the adverse effects of stool softeners?
Mild effect.
What is the mechanism of action of lubricant laxatives?
Coats stool.
What are the adverse effects of lubricant laxatives?
Aspiration risk.
What are the key components of the emetic pathway?
Chemoreceptor Trigger Zone (CTZ) → Dopamine/Serotonin activation.
Which drug classes are used to treat nausea and vomiting?
5-HT3 Antagonists (Ondansetron), Dopamine Antagonists, Antihistamines.
Which anti-nausea drugs are safe in pregnancy and children?
Ondansetron (Zofran) is safe in pregnancy and children.
