ANTIHISTAMINE Flashcards
What are autacoids?
Potent endogenous substances that act locally with complex physiological and pathophysiological functions outside traditional immune or autonomic groups.
What are examples of amine autacoids?
Histamine and serotonin (5-hydroxytryptamine).
What is histamine and where is it stored?
A ubiquitous amine formed from histidine; stored in mast cells
What triggers histamine release?
Chemical and physical agents such as injury or immune responses.
What are histamine’s effects on the cardiovascular system?
Decreases systolic and diastolic blood pressure increases heart rate and contractility as a reflex.
What are histamine’s effects on the GI tract?
Increases gastric acid secretion via H2 receptors; causes smooth muscle contraction.
What are histamine’s effects on the bronchi?
Causes smooth muscle contraction and secretion potentially leading to bronchoconstriction (e.g.
What are histamine’s effects on nerve endings?
Causes pain and itching.
What are toxic effects of histamine?
Flushing
headache
What are H1 receptor antagonists?
Drugs that competitively and reversibly block H1 receptors to antagonize histamine effects often divided into first and second generations.
What are the classifications of H1 receptor antagonists?
Potent sedative (e.g. diphenhydramine)
What pharmacological actions are associated with first-generation H1 antihistamines?
Sedation
anti-nausea
What are the anticholinergic effects of first-generation antihistamines?
Dry mouth
urinary retention
Why are antihistamines not used for asthma?
They are not strong bronchodilators.
What is cyproheptadine used for?
Treatment of skin allergies
cold urticaria
What are common side effects of antihistamines?
Sedation antimuscarinic effects (dry mouth
Why do first-generation antihistamines have more side effects?
They have poor selectivity for H1 receptors and block other receptors (e.g. cholinergic
What are examples of clinical uses of H1 antihistamines?
Treatment of allergic rhinitis urticaria
What are drug interactions with antihistamines?
Increased sedation with alcohol or other sedatives; liver enzyme inhibitors increase arrhythmia risk with some second-generation antihistamines.
What are examples of second-generation non-sedative antihistamines?
Terfenadine
loratadine
What is the mechanism of action of H1 receptor antagonists?
They block H1 receptors reducing histamine-induced effects like capillary permeability
How are antihistamines metabolized?
Primarily metabolized in the liver; degradation products are excreted in urine.
What are the pharmacodynamics of first-generation antihistamines?
Block H1 receptors may also block muscarinic
What are the pharmacokinetics of antihistamines?
Well-absorbed orally and parenterally with significant liver metabolism and urinary excretion of metabolites.
What are the symptoms of histamine toxicity?
Flushing
hypotension
