6625881
Description
Flashcards by Andrew Street, updated more than 1 year ago
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Created by Andrew Street
about 8 years ago
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| Question | Answer |
| Give eg's of & indications for antihistamines. | eg's: cetirizine, loratadine, fexofenadine, chlorphenamine Indications: • Allergies - especially hay fever • Pruritus & urticaria - eg caused by bites, infxns, drug allergies • Anaphylaxis - adjunctive Rx after use of adrenaline & other life saving measures • Other drugs in this class may be used for N & V (see Antiemetics, histamine H1-receptor antagonists) |
| MOA of antihistamines. | The term ‘antihistamine’ is generally used to mean an antagonist of the H1 receptor. H2-receptor antagonists have different uses & are discussed separately. Histamine is released from storage granules in mast cells as a result of antigen binding to IgE on the cell surface. Mainly via H1 receptors, histamine induces the features of immediate-type (type 1) hypersensitivity: ^capillary permeability causing oedema formation (wheal), vasodilatation causing erythema (flare), & itch due to sensory nerve stimulation. When histamine is released in the nasopharynx, as in hay fever, it causes nasal irritation, sneezing, rhinorrhoea, congestion, conjunctivitis & itch. In the skin, it causes urticaria. Widespread histamine release, as in anaphylaxis, produces generalised vasodilatation & vascular leakage, with consequent hypotension. Antihistamines work in these conditions by antagonism at the H1 receptor, blocking the effects of excess histamine. In anaphylaxis, their effect is too slow to be life-saving, so adrenaline is the more important first-line treatment. |
| SE's of antihistamines. | • Sedation - especially with 1st generation antihistamines (eg chlorphenamine). 2nd generation drugs (inc loratadine, certirizine, fexofenadine) tend to cause less drowsiness as they don't cross the BBB. |
| CI's, cautions, & important interactions of antihistamines. | CI's: • Sedating antihistamines (e.g. chlorphenamine) should be avoided in severe liver DS, as they may precipitate hepatic encephalopathy Cautions: • None Important interactions: The antihistamines mentioned here are not subject to any major drug interactions. |
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