Antihistamines Flashcards
Which antibody is a major role player for the release of histamine?
IgE attaches to a mast cell.
How are mast cells activated to release histamine?
- Mast cells are resident cells that roam waiting for a pathogen.
- Post a pathogen being detected mast cells have their FceR1 bound by the FC portion of the IgE antibody(produced by naive B-cells post activation).
- Upon binding mast cells release histamine which would result in:
-Inflammatory effects
-N & V
What is the receptor classification of histamine
G-protein coupled receptors
What is a G-protein coupled receptor?
Receptors that respond to a sign form a neurotransmitter/ligand and have a response attained via second-messenger( cAMP, cGMP, DAG, IP3)
What are the four types of histamine receptors and their sites?
H1- Smooth muscle contraction(bronchi, gut, large blood vessels) & Relaxes small arterioles
H2-Gastric acid secretion
H3- Localised on nerve terminals, modulates neurotransmitter release in CNS
H4-Expressed in mast cells, basophils, eosinophils-inflammatory
Where are H1 receptors expressed mainly?
Endothelial cells
Brain
Vascular cells
Peripheral nerve terminals
What are the effects of H1 receptors?
Brain
Vessels
Skin
Bronchus
- Brain
-Causes wakefulness and appetite suppression - Vessels
-Causing blood vessels to dilate permeability leading to redness and oedema - Skin
NO causes pain & itching on the skin - Bronchus
Causes bronchoconstriction
Where is the H2 receptor localized and what is the main effects?
Mainly in gastric parietal cells
Release of histamine causes increased gastric secreteion
What are the mediators of histamine release?
- Allergic reaction
- Tissue injury
- Drugs & foreign chemicals
- Venom/wasp
What are examples of drugs that cause histamine release?
Tubocurarine
Succinlycholine
Morphine
Antibiotics (some)
Radiocontrast media
Carbohydrate plasma expander
Histamine-1 antagonists?
Competitive antagonist
When do you increase efficacy of H1 antagonist drugs?
When given before histamine release
What effect does it have on histamine released from storage site?
No effect
H1 antagonist and LA’S?
Many H1 antagonists are local anesthetics
What effect does H1 antagonist have H2 receptors?
Negligible effects on H2 receptors
H1 Antagonists admin?
Oral
IV
Topical administrations
What is the half-life for 1st generation antihistamines?
4-12hrs(short acting)
Which receptors do 1st generation drugs block?
Histamine receptors
Cholinergic receptors
Alpha-adrenergic receptors
Serotonin receptors
Calcium channel blockers
What are the S/E of 1st gen H1 antagonist?
- Cholinergic/Muscuranic blockade:
-Xerostomia
-Urinary retention
-Sinus tachycardia - 5-HT blockade:
-Increased appetite
-Increased weight gain - Alpha-blockade
-Postural Hypotension
-Increased dizziness - Cardiac ion channel blockade(Na+ & K+)
-Increased Ventilation arrhythmia
-Increase QT interval(the section on an electrocardiogram (ECG) report that represents the time it takes your heart muscle to contract and then recover) - CNS
-Decreased alertness, cognition, learning, memory and psychomotor
-Increased impairment with or without sedation
H1 antagonist CI?
BDZ
Alcohol
Which drugs are H1 antagonists?
My Drugs(3) Come(4) Pretty Bloody first there, Ace!
Meclizine
Diphenhydramine
Dimenhydrinate
Doxylamine
Cinnarizine
Chlorpheniramine
Cyclizine
Cyproheptadine
Promethazine
Betahistine
Tripolidine
Alimemazine
Which H1 antagonist drugs have decreased sedative and autonomic effects?
All the C drugs
Chlorpheniramine
Cyclizine
Cyproheptadine
Which H1 antagonist is a good antiemetic ?
Cyclizine
Which H1 antagonist has anti-serotonin activity?
Cyproheptadine
