Allergy: Histamines and Antihistamines Flashcards
What is an allergy?
disorder of the immune system resulting in excessive histamine release
What are some common allergic reactions?
eczema, hives, asthma, hay fever
What are the 1st generation of antihistamines?
chlorpheniramine, diphenhydramine, hydroxyzine
high drowsy children
What are the 2nd generation of antihistamines?
cetirizine, azelastine, loratadine, fexofenadine (CALF)
What are autocoids produced by?
neural and non-neural tissues
What is included in autocoids?
histamines, serotonin, prostaglandins, leukotrienes
What is histamine released in response to?
injury and allergic reaction
What can a high conc. of histamine lead to?
anaphylactic shock
Histamines come from what amino acid?
histidine
What enzyme is responsible for the formation of histamines?
L-histidine decarboxylase
What stimuli is released during the release of histamines?
increase the cGMP which will increase histamine
Histamine is an agonist for what receptor?
G-protein coupled receptors
What is histamine metabolized by?
N-methyltransferase
What site does an agonist have affinity for?
active site
What is the role of H1 receptors?
involved in allergic reactions causing dermatitis, rhinit, conjunctivitis
What results from H1 receptors?
- vasodilation: decrease in blood pressure
- increase vascular permeability
- nerve ending cause pruritus and lungs initiates the cough reflex
- bronchoconstriction
Antihistamines are what type of agonists for the H1 receptor?
inverse agonist
shifts equil. to inactive
Which generation of antihistamines can cross the BBB?
first gen
Is the 2nd generation of antihistamines sedative?
NO
Why is the first general distributed across the BBB?
due to higher lipid solubility
How are antihistamines eliminated?
metabolized in the liver by N-methyltransferase
Since antihistamines are inverse agonist, what site do they have affinity for?
inactive site
How do antihistamines affect the block production of cGMP?
decrease it
What are 1st generation of antihistamines used for?
allergic rhinitis, nausea, vomiting, and sedation
What are 1st generation of antihistamines used to prevent?
motion sickness and vertigo
What are 2nd generation of antihistamines used for?
treat allergies
What are side effects of 1st generation antihistamines?
dry mouth, tachycardia, blurred vision, urinary retention
diphenhydramine can block muscarinic receptors
What are side effects of 2nd generation antihistamines?
azelastine causes dizziness, headache, nasal irritation, dry-mouth, weight gain
