Absorption, distribution, metabolism and excretion of [14C]levocetirizine, the R enantiomer of cetirizine, in healthy volunteers
Abstract
The main goal of the present study was to investigate the absorption and disposition of levocetirizine dihydrochloride, the R enantiomer of cetirizine dihydrochloride, following a single oral administration (5 mg) of the 14C-labelled compound in healthy volunteers. Configurational stability was also investigated. Levocetirizine was rapidly and extensively absorbed: 85.4% and 12.9% of the radioactive dose were recovered 168 h post-dose in urine and faeces, respectively. Levocetirizine and/or its metabolites were not, or only very poorly, associated with blood cells, as the blood-to-plasma ratio was 0.51 to 0.68. The mean apparent volume of distribution (Vz/F) was 26.9 1 (0.3 l/kg) indicating that the distribution of levocetirizine is restrictive. The protein binding of radiolabelled levocetirizine was 96.1% l h after administration. In vitro, at concentrations ranging from 0.2 microg/ml to 1 microg/ml, the protein binding was 94.8% to 95.0%. Levocetirizine is very poorly metabolised. The cumulative 48-h excretion as parent compound accounted for 85.8% of the oral dose, equivalent to 95% of the total radioactivity excreted at this time. At least 13 minor metabolites were detected in urine and represented 2.4% of the dose at 48 h. The metabolic pathways involved in levocetirizine metabolism are oxidation (hydroxylation, O-dealkylation, N-oxidation and N-dealkylation), glucuroconjugation, taurine conjugation and glutathione conjugation with formation of the mercapturic acids.…
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