Cetirizine hydrochloride pharmacology
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Cetirizine Hydrochloride Mechanism of Action and Antihistaminic Activity
Cetirizine hydrochloride is a second-generation antihistamine that works primarily as a selective histamine H1-receptor antagonist. It blocks the action of histamine, a chemical responsible for allergic symptoms, by binding to peripheral H1 receptors. This action leads to a marked reduction in allergic responses such as wheal and flare reactions, sneezing, rhinorrhea, and itching, with a fast onset and long-lasting effect. Cetirizine is more potent in inhibiting these responses compared to other antihistamines like terfenadine, loratadine, epinastine, and ebastine 15.
Anti-Inflammatory and Eosinophil-Modulating Properties
Beyond its antihistaminic effects, cetirizine also inhibits eosinophil chemotaxis and infiltration, which are important in allergic inflammation. This property helps reduce persistent inflammation in conditions like allergic rhinitis and urticaria, and may also benefit patients with asthma and atopic dermatitis by decreasing hypersensitivity and normalizing inflammation in the upper respiratory tract and skin 15.
Pharmacokinetics: Absorption, Distribution, and Elimination
Cetirizine is rapidly absorbed after oral administration, with significant clinical effects seen within 20 minutes and lasting up to 24 hours. It has high oral bioavailability (over 70%) and is mainly excreted unchanged in the urine, with a mean elimination half-life of about 7–8.3 hours. The drug is highly bound to plasma proteins (88–96%) and shows minimal interaction with liver enzymes, reducing the risk of drug-drug interactions 235.
Central Nervous System (CNS) Effects and Safety Profile
Cetirizine’s zwitterionic structure limits its penetration into the central nervous system, resulting in minimal sedative effects compared to first-generation antihistamines. Studies show negligible brain penetration and low risk of CNS impairment at recommended doses. It also has negligible anticholinergic and antiserotonergic activity, and does not cause significant cardiac side effects or teratogenicity 25.
Clinical Efficacy and Use in Allergic Disorders
Cetirizine is effective in treating symptoms of allergic rhinitis, urticaria, and other allergic skin diseases. It provides fast and strong relief from histamine-induced symptoms and can reduce the need for topical anti-inflammatory medications in atopic dermatitis. Its anti-inflammatory properties may also help in the management and prevention of mild asthma 15.
Formulation and Administration Considerations
Cetirizine is available in oral formulations and, in some cases, as a transdermal preparation combined with other agents like boric acid for skin hypersensitivity diseases. Transdermal delivery can reduce adverse effects associated with oral or injectable administration and is particularly suitable for infants, the elderly, and patients with difficulty swallowing .
Bioequivalence and Generic Availability
Generic brands of cetirizine hydrochloride have been shown to be bioequivalent to innovator brands, with similar pharmacokinetic profiles and urinary excretion patterns. This ensures that generic options are effective and suitable alternatives for patients .
Conclusion
Cetirizine hydrochloride is a potent, selective, and well-tolerated second-generation antihistamine. Its rapid onset, long duration of action, minimal CNS effects, and additional anti-inflammatory properties make it a preferred choice for managing a range of allergic disorders. Its favorable pharmacokinetic profile and availability in both branded and generic forms further support its widespread clinical use 12345.
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