Anti-histamines Part 1 Flashcards
What is the histamine precursor?
Histidine
What enzyme converts histidine to histamine?
Histidine Decarboxylase
What are 4 functions of histamine?
- immediate allergic and inflammatory reactions
- gastric acid secretion
- neurotransmission and neuromodulation
- chemotactic factor for recruitment of neutrophils, eosinophils, basophils, monocytes, and lymphocytes
Where is histamine stored in the blood?
In basophils- preformed granules
Where is histamine stored in the tissue?
Mast cells
Where is histamine stored? (4 locations)
- blood basophils
- tissue mast cells
- gastric mucosal cells
- neurotransmitter vesicles
What does the Histamine 1 Receptor cause an increase in?
IP3/DAG
Which histamine receptors causes a decrease in cAMP?
H3 and H4
What receptor leads to an increased cAMP?
H2
What effects does histamine have in the cardiovascular system?
- vasodilation of arterioles and precapillary sphincters via H1
- increased vascular permeability via H1 (hives)
- increased heart rate
What histamine receptor is involved in increased vascular permeability?
H1
What are the effects of histamine in the GI?
increased acid secretion via H2
What histamine receptor is involved in increasing gastric acid secretion?
H2
Which histamine receptor leads to bronchoconstriction?
H1
What are the nervous system effects of histamine?
stimulation of sensory nerve endings via H1
What cell types are involved in the wheal and flare reaction?
vasculature- dilation
endothelium- permeability –> edema
sensory nerve endings - red, irregular flare surrounds wheal (can have itching)
What two mediators are increased with histamine to cause vasodilation?
Nitric oxide and prostaglandin
What causes the edema with histamine?
Endothelial- H1 receptor
Contraction of endothelial cells which causes vascular permeability
Chlorpheniramine
1st Gen H1 receptor competitive antagonist
Diphenhydramine
1st Gen H1 receptor competitive antagonist
What is the duration of 1st Gen H1 receptor competitive antagonists?
Short duration of 3-6 hours
What effects are related to 1st Gen H1 receptor competitive antagonists?
anticholinergic anti a-adrenergic : anti-serotonergic : anti seretonin effects sedation antiemetic- against vomiting and nausea anti-motion sickness
What drug class has a long duration of 12-24 hours?
2nd/3rd Gen H1 receptor competitive antagonists
loratadine
2nd/3rd Gen H1 receptor competitive antagonists
fexofenadine
2nd/3rd Gen H1 receptor competitive antagonists
cetirizine
2nd/3rd Gen H1 receptor competitive antagonists
What is the difference in side effects between 1st Gen and 2nd/3rd Gen H1 receptor competitive antagonists?
2nd/3rd Gen H1 receptor competitive antagonists have LITTLE TO NO anticholinergic, anti a-adrenergic, anti-serotonergic effects. Less sedation. And are not useful for nausea or motion sickness.
H2 Receptor Antagonists are thought to be useful for…
reducing NSAID induced dyspepsia
Gastric ulcers are due to
NSAID use
Most peptic ulcers are due to…
H. Pylori infection
H2 receptor antagonists are associated with…
esophageal reflux
few side effects
infrequent GI irritation
cimetidine
potent inhibitor of P450 metabolism
