130018-77-8

The (R)-enantiomer of the second-generation antihistamine cetirizine, levocetirizine, was first introduced in Germany for seasonal allergic rhinitis (including ocular symptoms), perennial allergic rhinitis and chronic idiopathic urticaria. The dihydrochloride salt can be prepared in four steps from optically active 4-chlorobenzhydrylamine obtained by resolution of its racemate with (+)-tartaric acid. Levocetirizine (eutomer) is a 2-fold more potent H₁ antagonist than cetirizine whereas the other enantiomer (distomer) is 10-fold less potent compared to levocetirizine. Pharmacodynamic studies on healthy volunteers showed that compared to cetirizine, half the dose of levocetirizine (5 mg) was necessary to obtain similar inhibitory effects in the skin test of histamine-induced wheal and flare as well as on histamine-induced nasal congestion and nasal resistance. There was no evidence of chiral inversion of levocetirizine in vivo in several species including human. The daily dose of drug is rapidly and extensively absorbed in human. Interestingly, its volume of distribution (0.41 kg/L) is smaller than that of the distomer (0.60 kg/L). The low volume of distribution is considered as favorable for an antihistamine both in terms of efficacy and safety. Due to its high metabolic stability and lack of effect on the activities of the major CYP isoenzymes, levocetirizine is unlikely to cause interactions with other administered drugs. No clinically relevant effect on electrocardiograms of healthy volunteers was detected.

Off-White Solid

Sepracor (US)

A nonsedating type histamine H1-receptor antagonist. A major metabolite of Hydroxyzine. Pharmacological activity resides primarily in the (R)-isomer. Antihystaminic.

H1 antihistamine, antiallergic

Labeled cetirizine, intended for use as an internal standard for the quantification of cetirizine by GC- or LC-mass spectrometry.

ChEBI: 2-[2-[4-[(R)-(4-chlorophenyl)-phenylmethyl]-1-piperazinyl]ethoxy]acetic acid is a diarylmethane.

Xusal

Antihistamine:
Symptomatic relief of allergy such as hay fever, urticaria

The extent of metabolism of levocetirizine in humans is less than 14% of the dose. Metabolic pathways include aromatic oxidation, N- and O- dealkylation and taurine conjugation. Dealkylation pathways are primarily mediated by CYP 3A4 while aromatic oxidation involved multiple and/or unidentified CYP isoforms. The major route of excretion of levocetirizine and metabolites is via urine. Excretion via faeces accounts for only 12.9% of the dose. Levocetirizine is excreted both by glomerular filtration and active tubular secretion.