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Histamine and Antihistamines
Flashcards from LEcture handout
17
Pharmacology
Graduate
02/23/2011

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Term
Histamines
Definition
present in many tissues
synthesized from histidine by L-histidine decarboxylase
Term
Main histamine storage site
Definition
Mast cell granules, release when mast cells are activated by specific allergens
Term
Physiological events in response to histamine
Definition
smooth muscle relaxation/contraction
blood vessel dilation
increased capillary permeability
wheal and flare
Term
H-1 receptors
Definition
Agonism causes an increase in intracellular calcium by activation of PLC
This is the most active receptor for histamine actions in smooth muscles
vasodilation, bronchoconstriction, +inotropic and chonotropic on heart
CNS stimulation/depression, motion sickness
Term
selective H1 antagonists
Definition
Mepyramine, chlorpheniramine, triplodine
Term
H-2 receptors
Definition
agonists cause increase in IC cAMP via Gs receptors
Stimulates gastric secretion, regulates blood pressure and CNS functions
Term
H-2 selective antagonists
Definition
Cimetidine, ranitidine, famotidine, nizatidine
Term
H-3 receptor
Definition
agonists cause a decrease in calcium influx into the cells
Involved in feedback inhibition of NT release
Term
H-3 selective antagonists
Definition
thioperamide, clobenpropit
Term
H-4 receptor
Definition
agonists cause eosinophil and mast cell chemotaxis mediated by Gi/o
Particularly treated in the case of rheumatoid arthritis and IBD
Term
Use of H1 blockers
Definition
First generation: rapid onset, 4-6 hour duration
Second generation:rapidly absorbed and duration of 4-24 hours
allergic conditions
motion sickness/vertigo/sedation
Term
Would you use an H1 blocker in acute anaphylaxis?
Definition
NO, because histamine is only one of the mediators released in a severe attack and antihistamines don't treat the underlying cause
Term
Side effects of H1
Definition
Sedation, GI effects, dry mouth (muscarinic side effect)
CNS stimulation with OD
Term
H2 Blockers Action
Definition
rapidly absorbed after oral intake, with peak levels in 1-3 hours and must be dose adjusted in renally impaired patients
Term
H2 therapeutic uses
Definition
Inhibit gastric acid secretion, especially at night, thus dosing once daily after dinner can aid in ulcer healing
Ulcer healing/GERD/prophylaxis
Term
Cimetidine
Definition
used to treat moderate to severe cases of hives
Term
Side effects of H2
Definition
usually minimal, may induce diarrhea, constipation, headache, drowsiness, fatigue, and muscle pain
Cimetidine May interfere with estrogen metabolism and cause gynecomastia/impotence
CimetidineInhibits CYPs, more drug-drug interaction
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