GI

Question 1

H2 blockers

Answer 1

Drugs: cimetidine, ranitidine, famotidine, nizatidine

MoA: REVERSIBLE block of histamine H2-receptors -> decreased H+ secretion by parietal cells

Use: Peptic ulcer, gastritis, mild esophageal reflux.

Toxicity:
Cimetidine: potent inhibitor of cytochrome P-450 (multiple drug interactions); it also has antiandrogenic effects (prolactin release, gynecomastia, impotence, decreased libido in males); can cross BBB (confusion, dizziness, headaches) & placenta

Cimetidine & ranitidine: decrease renal excretion of creatinine.

Other H2 blockers are relatively free of these effects.

Question 2

PPIs

Answer 2

Drugs: omeprazole, lansoprazole, esomeprazole, pantoprazole, dexlansoprazole

MoA: IRREVERSIBLY inhibits H+/ K+ ATPase in stomach parietal cells.

Use: Peptic ulcer, gastritis, esophageal reflux, Zollinger-Ellison syndrome.

Toxicity: increased risk of C. diff infxn, pneumonia. Hip fractures, decreased serum Mg w/ long term use

Question 3

Bismuth, sucralfate

Answer 3

MoA: bind to ulcer base, providing physical protection and allowing HCO3- secretion to reestablish pH gradient in the mucous layer.

Use: increases ulcer healing, treats traveler’s diarrhea.

Question 4

Misoprostol

Answer 4

MoA: PGE1 analog. Increases production & secretion of gastric mucous barrier, decreases acid production.

Use: Prevention of NSAID-induced peptic ulcers; maintenance of a patent ductus arterioles. Also used to induce labor (ripens cervix).

Toxicity: Diarrhea. Contraindicated in women of childbearing potential (abortifacient).

Question 5

Octreotide

Answer 5

MoA: long-acting somatostatin analog.

Use: acute variceal bleeds, acromegaly, VIPoma, and carcinoid tumors

Toxicity: nausea, cramps, steatorrhea

Question 6

Antacid use

Answer 6

Can affect absorption, bioavailability, or urinary excretion of other drugs by altering gastric and urinary pH or by delaying gastric emptying.

All can cause hypokalemia.

Toxicity

Aluminum hydroxide: constipation and hypophosphatemia; proximal mm weakness, osteodystrophy, seizures. Mnemonic: aluMINIMUM amt of feces

Magnesium hydroxide: diarrhea, hyporeflexia, hypotension, cardiac arrest. Mnemonic: Mg= Must Go (to the bathroom)

Calcium carbonate: hypercalcemia, rebound acid hyper secretion. Can chelate and decrease effectiveness of other drugs (e.g. tetracycline)

Question 7

Osmotic laxatives

Answer 7

Drugs: magnesium hydroxide, magnesium citrate, polyethylene glycol, lactulose

MoA: provide osmotic load to draw water out.

Lactulose also treats hepatic encephalopathy since gut flora degrade it into metabolites (lactic acid and acetic acid) that promote nitrogen excretion as NH4+

Use: constipation

Toxicity: diarrhea, dehydration; may be abused by bulimics

Question 8

Infliximab

Answer 8

MoA: monoclonal antibody to TNF- alpha

Use: Crohn’s disease, ulcerative colitis, rheumatoid arthritis

Toxicity: infxn (including reactivation of latent TB), fever, hypotension

Question 9

Sulfasalazine

Answer 9

MoA: a combination of sulfapyridine (antibacterial) and 5-aminosalicylic acid (anti-inflamm). Activated by colonic bacteria.

Use: ulcerative colitis, Crohn’s disease

Toxicity: malaise, nausea, sulfonamide toxicity, reversible oligospermia

Question 10

Ondansetron

Answer 10

MoA: 5-HT3 antagonist. Powerful central-acting antiemetic.

Use: control vomiting postoperatively and in pts undergoing chemo

Toxicity: headache, constipation

Question 11

Metoclopramide

Answer 11

MoA: D2 receptor antagonist. Increases resting tone, contractility, LES tone, motility. Does NOT influence colon transport time.

Clinical use: diabetic and post-surgery gastroparesis, antiemetic

Toxicity: Increased parkinsonian effects. Restlessness, drowsiness, fatigue, depression, nausea, diarrhea. Drug interaxn w digoxin and diabetic agents. Contraindicated in pts w/ small bowel obstruction or Parkinson’s disease