H2 receptor antagonists Flashcards
Cimetidine
Cimetidine
Class: H2 receptor antagonist
MOA:
Blocks the actions of histamine at H2 receptors, which are located at
- gastric parietal cells
- cardiac muscle cells
- Mast cells
- airway smooth muslce cells
these work at gastric parietal cells to block the H2 receptor and decrease cAMP and decrease calcium influx into cell, resulting in decrease of gastric acid secretion. Does nothing to change the pH or volume of the gastric acid ALREADY in the stomach, so these are usually paired with a pro-kinetic.
Pk:
Onset: 1 hour
DOA: 4 hours
E1/2T: 2 hours
PB: 20% small
vD: LARGE
Metabolized in liver, excreted 75% unchanged in urine.
Cimetidine is the LEAST POTENT H2 blocker.
It has a high first pass effect so given IV.
Dose:
300 mg IV over 10-15 minutes, 1-2 hours before surgery.
Must be given slowly to prevent H1 agonsim.
SE:
With renal failure - can have slow wake up form anesthesia
Fatigue/confusion/headache
transient increase in LFTs and decrease in HBF.
aRRTHYMIAS!!
rapid admin = bradycardia, hypotension.
C/I:
asthma r/t r/f unopposed H1 agonism.
Caution in renal failure r/t excretion
Caution in liver failure r/t transient effects
Cimetidine INHIBITS CYP450, will alter the metabolism of propanolol, warfarin, dizepam, lidocaine, TCAs, CCBs, phenyotin.
Ranitidine
Ranitidine
Class: Anti-histamine, H2 receptor antagonist.
MOA:
Blocks the action of histamine at H2 receptors, H2 receptors are located
- gastric parietal cells
- cardiac muscle cells
- mast cells
- airway smooth muscle cells
Blocks the action of histmaine at h2 receptors in gastric parietal cells, decreases cAMP, decreases calcium influx and prevents the secretion of gastric acid. Does not raise the ph or decrease the volume of the acid already int he stomach, so is usually paired with a prokinetic if being used for asp. prophylaxis.
Uses
duodenal ulcers
aspiration prophyxlasi in anesthesia
Pk:
onset:1 hours
DOA: 4 hours
e1/2t: 2 hours
PB: 20%
vd: LARGE
Metabolized by liver, 50% excreted unchanged in urine.
High first pass effect so given IV.
Dose:
50 mg IV over 10-15 mintues, 1-2 hours pre op.
must be given over 10-15 minutes r/t r/f H1 agonism,
1-2 hours pre op r/t onset time.
SE:
Delayed awakening from anesthesia in pts with renal failur e
headache/confusion/fatigue
Arrthymias
if given rapidly - bradycardia, hypotension.
Transient decrease in HBF with transient increase LFTs.
C/I:
asthma r/f unopposed h1 AGONISM
pts with renal failure r/t excretion
pts with hepatic failure r/t HBF
ranitidine has been removed from market r/t r/f CA
Famotidine
Famotidine
H2 receptor antagonist
Blocks the action of histamine at H2 receptors, H2 receptors are located at
- gastric parietal cells
- cardiac muscle cells
- airway smooth muscle cells
- mast cells
Blocks the action of histmaine at H2 receptors in gastric parietal cells, decreases cAMP and decreases the calcium influx, decreasing the gastric acid secretion. Does nothing to alter the ph or volume of gastric acid already in the stomach. So if these are being used for aspiration prophylaxis prior to surgery they are usually paired with a pro-kinetic. Can also be used to tx duodenal ulcers.
Pk:
onset: 30 minutes
DOA: 8 hours
E1/2T: 2 hours
PB: 20%
vD: Large
metabolized by liver and excreted 75% unchanged in urine.
Dose:
20 mg IV over 2 minutes, 1 hour pre-op.
Must be given slowly to prevent H1 agonism.
SE:
If given too quickly - hypotension/bradycardia
arrhthymias
delayed awakening from anesthesia if pt has renal failure
confusion/headache/fatigue
transient decrease in hBF and increase in LFTs
C/I:
Caution in renal failure r/t excretion
caution in liver failure r/t decrease in HBF
caution in asthma r/t r/f unopposed H1 agonism
