Cetriliv Mechanism of Action

Pharmacology: Pharmacodynamics: Mechanism of Action: The second-generation H1-receptor antagonist cetirizine is a racemate, consisting of equal quantities of two enantiomers, levocetirizine [(R)-enantiomer] and dextrocetirizine [(S)-enantiomer]. In vitro and human pharmacodynamic studies (histamine-induced cutaneous and nasal responses) have provided evidence that levocetirizine is the more active enantiomer, accounting for most or all clinical antihistaminic activity of racemic cetirizine; this activity of levocetirizine is seen at half the dose of cetirizine.
In one in-vitro study, levocetirizine exhibited a 2-fold higher affinity for human H1-receptors than cetirizine, and was about 10-fold more potent than the (S)-enantiomer; levocetirizine dissociated more slowly from the H1-receptor than the (S)-enantiomer.
Oral levocetirizine 5 milligrams (mg) was reported more effective than oral loratadine 10 mg in preventing histamine-induced cutaneous responses (i.e. wheal, flare) in a small double-blind, pharmacodynamic study involving healthy subjects.
Racemic cetirizine [Zyrtec(R)], a metabolite of hydroxyzine, is a selective H1-antagonist which has shown efficacy in allergic rhinitis and chronic urticaria, with a relatively low propensity for adverse effects. No advantage of levocetirizine over racemic cetirizine was observed in pharmacodynamic comparisons in healthy subjects.
Pharmacokinetics: Levocetirizine is well-absorbed after single oral doses, with peak plasma levels occurring in about 1 hour; a volume of distribution of 0.3 L / kg and clearance of 0.6 ml / min / kg were reported. Similar to racemic cetirizine, hepatic metabolism is minimal, and most of a dose is excreted unchanged in the urine. A plasma elimination half-life of 7 hours has been reported after a single dose. Multiple-dose pharmacokinetic data are unavailable.
Toxicology: Preclinical Safety Data: Preclinical Data reveal no special hazard for humans based on conventional studies of pharmacology, repeated dose toxicity, genotoxicity and carcinogenic potential.