Small molecule
PubChem CID 2678
Cetirizine
Zyrtec
- Mechanism of action
- Second-generation H1 histamine receptor antagonist
- In plain language
- Blocks histamine from docking onto its receptors outside the brain, stopping the sneezing, itching, and swelling of an allergic reaction before it can start.
- How it works
- Cetirizine is a second-generation antihistamine that acts as a selective, competitive antagonist at peripheral histamine H1 receptors, with negligible affinity for muscarinic, serotonergic, or other receptor classes. By occupying H1 receptors on vascular endothelium, sensory nerve endings, and smooth muscle, it blocks histamine-mediated vasodilation, increased vascular permeability, and sensory nerve stimulation — the processes underlying the wheal-and-flare response, rhinorrhea, pruritus, and lacrimation of an allergic reaction. Unlike first-generation antihistamines, cetirizine shows negligible penetration across the blood-brain barrier, so it occupies few central H1 receptors and produces markedly less sedation. H1-receptor inhibition begins within about 20 minutes to 1 hour and persists at least 24 hours, supporting once-daily dosing.
- Therapeutic applications
- Indicated for relief of symptoms associated with seasonal allergic rhinitis and perennial allergic rhinitis — sneezing, rhinorrhea, postnasal discharge, nasal and ocular pruritus, and lacrimation — due to allergens such as pollen, dust mites, animal dander, and molds. Also indicated for treatment of the uncomplicated skin manifestations of chronic idiopathic urticaria, reducing the occurrence, severity, and duration of pruritus and hives.
- Class
- Small molecule
- Therapeutic area
- Allergy / Immunology
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