Antihistamines and Allergic Rhinitis/URI Drugs Flashcards
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Histaminergic neurons
Located exclusively in the posterior hypothalamus, associated with peak release at night as regulated by circadian rhythm
Agents that trigger histamine release without prior sensitization (3)
Drugs, radiocontrast media, direct cell injury
Efffects of H1 receptor stimulation
- Vasodilation
- increased capillary permeability
- bronchoconstriction
- increased itching or pain
Can you treat asthma with antihistamine?
No, the antihistamine has minimal benefit
effects of H2 stimulation (1)
Secretion of gastric acid
Can antihistamines treat anaphylaxis?
No, they have minimal impact and are used as primarily adjunctive therapy
2 classes of H1 antagonist
1st gen - diphenhydramine and chlorpheniramine
2nd gen - cetirizine, levocetirizine, fexofenadine, loratidine, desloratidine
Diff between 1st and 2nd gen H1 antagonists
- 1st gen are highly sedating, 2nd not very much
- 1st gen have anticholinergic effects leading to dry mouth, difficulty in micturition, tachycardia, constipation, virtually absent in 2nd generation
H1 antagonist mech of action
Competes with antihistamine for H1 receptors, does not inhibit histamine already attached to receptors so therefore should be taken 2 to 5 hours before allergen exposure (prophylactically)
Therapeutic uses of H1 antagonist (5)
- mild allergy
- severe allergy (supplemental)
- motion sickness
- insomnia
- useless for the common cold
ADR’s of H1 (primarily 1st gen but some 2nd gen) antagonist (4)
- sedation (1st gen)
- psychomoor performance
- GI disturbances
- anticholinergic effects (primarily 1st gen)
Drug interactions of H1 antagonists (2)
- CNS depressants
- alcohol
Name the 5 big 2nd gen H1 blockers (brand name and generic)
Fexofenadine (allegra) Cetirizine (zyrtec) Loratadine (claritin and alavert) Desloratadine (clarinex) Levocetirizine (xyzal)
Loratadine (claritin and Alavert) indications (2)
- allergic rhinitis
- chronic idiopathic urticaria
Cetirizine (zyrtec) indications (3)
- seasonal allergic rhinitis
- Perennial allergic rhinitis
- Chronic idiopathic urticaria