L22- GIT Drugs I (H2 receptor antagonists)

Question 1

H2 receptor antagonist goal / function

Answer 1

• suppresses Histamine –> reduce gastric acid secretion

- reduces ACh and Gastrin signal transduction –> reduce gastric acid production

Question 2

discuss H2 receptor antagonist binding and MOA

Answer 2

• highly selective competitive inhibitors of H2R

- inhibits Gs coupled protein receptor –> dec cAMP (dec gastric acid secretion)

Question 3

H2 receptor antagonist:

• (1) time of onset
• (2) duration of action
• (3) develops in use after about 2-6 wks (short-term drug)

Answer 3

1- 2.5hrs
2- 4-10hrs
3- Tachyphylaxis (less effective over time)

Question 4

list the H2 receptor antagonist drugs

Answer 4

Cimetidine (prototype)- many adverse effects

Ranitidine, Famotidine, Nizatidine (2nd generation)- no anti-androgenic, CNS adverse effects

Question 5

H2 receptor antagonist effect on basal and meal time gastric acid secretion

Answer 5

• strong reduction on basal secretion

- modest reduction on meal time secretion

Question 6

indicate the uses for H2 receptor antagonists

Answer 6

GERD
PUD
Nonulcer dyspepsia
Prophylaxis against stress related gastritis

Question 7

discuss the main adverse effect of ALL H2 receptor antagonist

Answer 7

inc gastric pH

• -> dec pepsin function
• -> including B12 extraction from food (meat)
• -> B12 deficiency and myelosuppression with long-term use

Question 8

list the adverse effects of Cimetidine (hint- 3 categories)

Answer 8

1- (anti-androgenic, pro-prolactin effects) gynecomastia, galactorrhea, male impotence

2- (crosses BBB) confusion, dizziness, HAs

3- (strong CYP450 inhibition) inc serum concentration of many drugs –> warfarin, diazepam, phenytoin