Antihistamines Flashcards
Diphenhydramine
- (Benadryl®)
- Sedating Antihistamines
Dimenhydrinate
- (Dramamine®)
- Sedating Antihistamines
Promethazine
- (Phenergan®)
- Sedating Antihistamines
Loratadine
- (Claritin®)
- Second-generation (Non-Sedating) H1 Antagonists
Cetirizine
- (Zyrtec®)
- Second-generation (Non-Sedating) H1 Antagonists
Azelastine (Astelin NS®; Astepro®)
Nasal H1 Antagonists
The allergic response is mediated by what antibody
IgE
In allergic response, IgE binds to Fc receptors on surface of what cells
- mast cells
- basophils
What happens when antigen binds to IgE
- activates protein kinases to increase IP3 and Ca2+ -> activates Phospholipase A2 -> increases
- platelet activating factor
- leukotrienes
- kinins
- mast cell degranulation -> histamine
H1 histamine receptor acts through what messenger system
Gq
H1 histamine receptor is found in what tissues
- smooth muscle
-
endothelium
- activates NO
- vasodilation
-
brain
- wakefullness
- appetite control
H2 histamine receptor activation is coupled with what messenger system
Gs -> increases cAMP
H2 histamine receptor activation causes what
- gastric acid secretion
- vasodilation (at higher concentrations)
List the 4 main effects of histamine and which receptors are responsible
- vasodilation (H1 and H2)
- Bronchospasm (H1)
- Gastric acid secretion (H2)
- Itching
vasodilation effect of H1 and H2 stimulation leads to what effects
- decreased BP, reflex tachycardia
- increased capillary permeability
- edema and swelling
what is the triple response that occurs after intradermal injection of histamine.
- Dilation of capillaries in immediate area (flush), which appears in seconds. This is a direct histamine effect.
- Dilation of arterioles causing redness over a wider area (flare) develops more slowly, due to stimulation of axon reflexes
- Swelling (wheal) in the area of capillary dilation; appears after 1-2 minutes and is the result of edema due to increased capillary permeability.
MOA of antihistamines
- inverse agonist
- decrease normal histamine activity
- block effects of released histamine
- Since they compete with histamine, the ability to block histamine depends on the amount of histamine present
what is unique about the first generation H1 antagonists
- enter the brain
- block muscarinic receptors -> sedation
List the sedating first generation H1 antagonists
- Diphenhydramine
- Promethazine
- Dimenhydrinate
which first generation H1 antagonists are useful against motion sickness
- Dimenhydrinate
- Diphenhydramine
**due to muscarinic blockade
which first generation H1 antagonists is used as an antiemetic
Promethazine
How are second generation H1 antagonists different from first generation
- second generation
-
do not enter brain
- far less sedation
-
no anticholinergic effects
- not useful for motion sickness
-
do not enter brain
Most antihistamines are excreted by the liver, what are the three that are excreted by the kidney and thus are better for patients with liver disease
- Cetirizine
- Levocetrizine
- Acrivastine
antihistamines for allergic rhinitis are best when used
prophylactically
antihistamines taken for motion sickness should be taken when
- prophylactic, BEFORE you get sick
side effects of first generation antihistamines
- Sedation
- Dry mouth -> anticholinergic
side effects of all antihistamines
- GI: nausea, inc appetite
- decrease seizure threshold
first generation antihistamines have what effect on CNS
CNS depressants
overdose of first generation antihistamines have what effect
- similar to atropine poisoning
- sedation, dry of salivary and bronchial secretions
overdose of second generation antihistamines have what effect
sinus tachycardia
MOA and route of administration of Azelastine
- nasal spary
- a non-competitive H1 blocker that also decreases the release of histamine from mast cells
- used for allergic rhinitis.
List the drugs that act to inhibit the release of histamine
- Azelastine
- Cetirizine
