Chapter 161 - gastrointestinal protectants

Question 1

MOA of H2 receptor antagonists

Answer 1

competitively blocks histamine 2 receptors on the gastric parietal cell

Question 2

Most potent H2RA

Answer 2

famotidine

Question 3

H2RA with longest duration of action

Answer 3

famotidine

Question 4

which 2 H2RAs are metabolised extensively in the liver

Answer 4

cimetidine, ranitidine

Question 5

cimetidine is sometimes used in acetominophen toxicity. why?

Answer 5

markedly inhibits hepatic cytochrome P-450 system which converts acetaminophen into toxic N-acetyl-p-benzoquinone-imine (NAPQI)

Question 6

side effects of cimetidine specifically

Answer 6

through P450 inhibition: decreases metabolism of theophylline, lidocaine, metronidazole etc –> toxicity
decreases hepatic blood flow by ~20%

Question 7

side effects of H2RAs in general

Answer 7

apathy, nausea, vomiting (+ CNS aberrations and cytopenias including thrombocytopenia in people)

Question 8

MOA of PPIs

Answer 8

irreversibly inhibit hydrogen-potassium adenosine triphosphatase on the luminal side of parietal cells, stopping secretion of hydrogen ions into the gastric lumen

Question 9

in people, are PPIs or misoprostol more effective for preventing gastric ulcers due to NSAID use?

Answer 9

misoprostol

Question 10

in people, are PPIs or misoprostol more effective for preventing duodenal ulcers due to NSAID use?

Answer 10

PPIs

Question 11

adverse effects of PPIs

Answer 11

diarrhoea, hypersensitivity reactions, increased gastric pH affects some drug absorption (ketoconazole, digoxin),
omeprazole inhibits hepatic P450 enzymes (decreases efficacy of clopidogrel and clearance of diazepam in people) may cause liver enzyme elevations and hypomagnesemia

Question 12

which PPIs have in vivo activity against Giardia & Trichomonas?

Answer 12

pantoprazole, rabeprazole

Question 13

two mechanisms by which sucralfate promotes ulcer/erosion healing?

Answer 13

physical barrier (protects from pepsin & bile acids)
stimulates local production of prostaglandins and binding to epidermal growth factor (increases mucosal repair)

Question 14

adverse affects of sucralfate

Answer 14

can absorb other drugs (e.g.- enrofloxacin)

may bind fat soluble vitamins

Question 15

sucralfate ingredient

Answer 15

octasulfate of sucrose combined with aluminium hydroxide

Question 16

MOA of misoprostol

Answer 16

prostaglandin E1 analog with antacid mucosal protective properties, acts directly on parietal cells and inhibits both nocturnal acid secretion and secretion in response to food, pentagastrin and histamine

Question 17

adverse effects of misoprostol

Answer 17

diarrhea, uterine contraction, abortion in pregnant females

Question 18

why are over the counter antacids not recommended in companion animals?

Answer 18

ineffective: short half-lives compared to PPIs and H2RAs

may delay or prevent absorption of other drugs

Question 19

studies on the use of long-term acid-suppression therapy in humans found what?

Answer 19

no increased risk of bacterial pneumonia following aspiration but increased risk of Clostridium difficile infection in some populations