2 - Antihistamines Flashcards
Histamine is synthesised and stored by human cutaneous mast cells
True
Mast cells synthesise histamine from histidine via the enzyme histidine decarboxylase
True
Histamine is bound to granules composed of glycosaminoglycans
True
Released histamine undergoes rapid local degradation
True
Cutaneous mast cells express IgE receptor on the cell surface
True
Cross linking of adjacent IgE receptors by antigen culminates in the release of histamine and other mediators I.e. Proteases and cytokines
True
Histamine H1 receptor is expressed in human skin
True
Histamine H2 receptor is expressed in human skin
True
H1 receptors mediate histamine-induced itching and the axon reflex flare
True
H2 receptors have no role in histamine-evoked itching
True
H2 receptors regulate T-lymphocyte activity
True
Both H1 and H2 receptors participate in histamine-evoked vasodilation and increased vascular permeability
True
H1 and H2 antihistamines are inverse agonists
True
H1 and H2 antihistamines are inverse agonists and downregulate the constitutive activated state of the corresponding receptor
True
Regular H1 antihistamine maximises the therapeutic response
True (inverse agonist mode of action)
H1 antihistamines substantially relieves itching related to chronic urticaria but not the complete suppression of redness and wheals
True
H1 antihistamines incompletely suppresses the redness of chronic urticaria
True (incompletely suppresses redness which suggests that other mediators besides histamine is involved in the pathology)
H1 antihistamines incompletely suppresses the wheals of chronic urticaria
True (incompletely suppresses the wheals which suggests that other mediators besides histamine is involved in the pathology)
First generation antihistamines are ethers based on the imidazole ring structure of histamine
True
Cimetidine and ranitidine are both H2 antihistamines
True
H2 antihistamines I.e. Cimetidine and ranitidine have not been successful either alone of in combination with H1 antihistamines in the treatment of urticaria
True (even though H2 antihistamines are expressed in skin blood vessels and may influence histamine-mediated vasodilation, they have been disappointing in practice for treatment of urticaria)
H2 antihistamines I.e. Cimetidine, ranitidine have less adverse effects than H1 antihistamines I.e. Hydroxyzine, Promethazine (sedating)
True
Itching is unresponsive to H2 antihistamines
True
The clinical value of the first generation H1 antihistamines is significantly limited by their adverse effects and atropine-like complications
True
First generation H1 antihistamines can cause impaired cognitive function
True
First generation H1 antihistamines can cause sedation
True
First generation H1 antihistamines can cause weight gain
True
First generation H1 antihistamines can cause dry mouth (atropine-like effect due to anticholinergic blockade)
True
First generation H1 antihistamines can cause blurred vision (atropine-like effect due to anticholinergic blockade)
True
First generation H1 antihistamines can cause constipation (atropine-like effect due to anticholinergic blockade)
True
First generation H1 antihistamines can cause urinary retention (atropine-like effect due to anticholinergic blockade)
True
First generation H1 antihistamines are sedating
True
Second generation H1 antihistamines are less sedating
True
Second generation H1 antihistamines have a negligible propensity to induce drowsiness and other troublesome effects of the first generation H1 antihistamines
True
The sedative action of the the first generation H1 antihistamines is due to the function of histamine as a neurotransmitter
True
H1 receptors are highly expressed in the cerebral cortex
True
The second generation H1 antihistamines have a low capacity to cross the blood brain barrier due to minimal lipophilicity
True (hence reduce sedation and cognitive impairment effect)
The first generation H1 antihistamines are more lipophilic than the second generation H1 antihistamines
True (hence first generation H1antihistamines can cross the blood brain barrier and affect the cerebral cortex)
The first generation H1 antihistamines have anticholinergic effects
True (first generation H1 antihistamines have anticholinergic effects of dry mouth, blurred vision, constipation, urinary retention)
The second generation H1 antihistamines have little or no affinity for muscarinic cholinergic receptors
True (therefore no anticholinergic effects, unlike first generation H1 antihistamines)
Ethanolamine, Piperidine, Phenothiazine, Alkylamine and Piperazine are 5 classes of first generation H1 antihistamines (all sedating)
True
Diphenhydramine is a first generation H1 antihistamine from the Ethanolamine class (sedating)
True
Cyproheptadine is a first generation H1 antihistamine from the Piperadine class (sedating)
True
Promethazine is a first generation H1 antihistamine from the Phenothiazine class (sedating)
True
Chlorpheniramine is a first generation H1 antihistamine from the Alkylamine class (sedating)
True