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Objective—To develop a high-performance liquid chromatography (HPLC) assay for cetirizine in feline plasma and determine the pharmacokinetics of cetirizine in healthy cats after oral administration of a single dose (5 mg) of cetirizine dihydrochloride.

Animals—9 healthy cats.

Procedures—Heparinized blood samples were collected prior to and 0.5, 1, 2, 4, 6, 8, 10, and 24 hours after oral administration of 5 mg of cetirizine dihydrochloride to each cat (dosage range, 0.6 to 1.4 mg/kg). Plasma was harvested and analyzed by reverse-phase HPLC. Plasma concentrations of cetirizine were analyzed with a compartmental pharmacokinetic model. Protein binding was measured by ultrafiltration with a microcentrifugation system.

Results—No adverse effects were detected after drug administration in the cats. Mean ± SD terminal half-life was 10.06 ± 4.05 hours, and mean peak plasma concentration was 3.30 ± 1.55 μg/mL. Mean volume of distribution and clearance (per fraction absorbed) were 0.24 ± 0.09 L/kg and 0.30 ± 0.09 mL/kg/min, respectively. Mean plasma concentrations were approximately 2.0 μg/mL or higher for 10 hours and were maintained at > 0.72 μg/mL for 24 hours. Protein binding was approximately 88%.

Conclusions and Clinical Relevance—A single dose of cetirizine dihydrochloride (approx 1 mg/kg, which corresponded to approximately 0.87 mg of cetirizine base/kg) was administered orally to cats. It was tolerated well and maintained plasma concentrations higher than those considered effective in humans for 24 hours after dosing. The half-life of cetirizine in cats is compatible with once-daily dosing, and the extent of protein binding is high.

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in American Journal of Veterinary Research