Gastrointestinal Drugs

Question 0

What is the mechanism of action of Proton pump inhibitors on GI Tract? Give examples.

Answer 0

They inhibit H+-K+-ATPase enzyme (Proton pump) of the parietal cell thereby suppressing secretion of hydrogen ions into the gastric lumen.
This reduces acid production and helps in healing peptic ulcers; used to treat GERD, Duodenal ulcer, and hypersecretory states, e.g. Zollinger Ellison syndrome.

Question 1

What is the mechanism of action of H2-receptor antagonist on GI tract? Examples?

Answer 1

They prevent histamine-induced acid release by blocking H2 receptors.

• Cimetidine (Tagamet): inhibits cytochrome P-450 thereby causing an increased conc. of warfarin, theophyline, phenytoin, diazepam, propranol, etc.
• Ranitidine (Zantac): less inhibition of P-450
• Famotidine (Pepcid): no inhibitition of P-450

Question 2

What is the use of Misoprostol on the GI tract? What is its important adverse effect?

Answer 2

Increases HCO3 and mucin release. Reduces acid secretion; used for prevention of ulcers caused by aspiriin and other NSAIDS.

Adverse Effect: abortion/uterine contraction, diarrhea, etc.

Question 3

What are the mechanisms of antidiarrheal action of Diphenoxylate with atropine?

Answer 3

Diphenoxylate with atropine (Lomotil): antimotility agent: diphenoxylate is an agonist at opiate receptors in GI tract and atropine blocks muscarinic receptor. Both actions inhibit peristalsis
Indication: Diarrhea

Question 4

What are mechanisms of antidiarrheal actions of Bismuth subsalicylate?

Answer 4

Bismuth subsalicylate (Pepto-Bismol): Adsorbents: It works by decreasing the flow of fluids and electrolytes into the bowel, reduces inflammation within in the intestine, and may kill organisms that cause diarrhea.

Question 5

List important drugs in the treatment of ulcerative colitis and Crohn’s disease.

Answer 5

Drugs for inflammatory bowel disease:
The primary therapy for ulcerative colitis and Crohn’s disease uses steroids and the following anti-inflammatory drugs.
- Mesalamine (5-aminosalicyclic acid)
- Olsalazine (Dipentum)
- Balsalazine (Colazal)
- Sulfasalazine (Azulfadine)
- Infliximab (Remicade): a monoclonal antibody that binds to and inhibits TNF-alpha, a proinflammatory protein produced by immune cells. It is used to treat moderate to severe Crohn’s disease that is refractory to other medical treatment; also used to treat rheumatoid arthritis

Question 6

What are the mechanism of action and uses of Infliximab?

Answer 6

Infliximab (Remicade): a monoclonal antibody that binds to and inhibits TNF-alpha, a proinflammatory protein produced by immune cells. It is used to treat moderate to severe Crohn’s disease that is refractory to other medical treatment; also used to treat rheumatoid arthritis

Question 7

List the names of important laxatives and cathartics.

Answer 7

They accelerate the movement of food through GI Tract

• Psyllium (Metamucil): nondigested plant cell wall absorbs water into feces.
• Bisacodyl (Dulcolax): increases water and electrolytes in feces and increases intestinal motility
• Saline Solution/Milk of Magnesia: draws water into lumen
• Lactulose: hyperosmolarity draws water into colon
• Docusate (Colace): lubricates feces and prevents absorption of water from feces.

Question 8

List anti emetic drugs.

Answer 8

Meclizine (Antivert): Antihistamine
Chlorpomazine (Thorazine): Dopamine antagonist
Metoclopramide (Reglan): Dopamine antagonist
Dolasetron (Anzemet): Serotonin antagonist
Methylprednisolone (Tigan): Other

Question 9

What is MOA of serotonin antagonists?

Answer 9

Selective serotonin antagonists inhibit the action of serotonin at the 5-hydroxytryptamine3 (5-HT3) receptor in the small bowel, vagus nerve, and chemoreceptor trigger zone

Dolasetron (Anzemet)