Cetirizine in horses: pharmacokinetics and pharmacodynamics following repeated oral administration

The pharmacokinetics of the histamine H(1)-antagonist cetirizine and its effect on histamine-induced cutaneous wheal formation were studied in six healthy horses following repeated oral administration. After three consecutive administrations of cetirizine (0.2 mg/kg body weight, bw) every 12h, the trough plasma concentration of cetirizine was 16+/-4 ng/mL (mean+/-SD) and the wheal formation was inhibited by 45+/-23%. After four additional administrations of cetirizine (0.4 mg/kg bw) every 12 h, the trough plasma concentration was 48+/-15 ng/mL and the wheal formation was inhibited by 68+/-11%. The terminal half-life was about 5.8 h. A pharmacokinetic/pharmacodynamic link model showed that the maximal inhibition of wheal formation was about 95% and the EC(50) about 18 ng/mL. It is concluded that cetirizine in doses of 0.2-0.4 mg/kg bw administered at 12 h intervals exhibits favourable pharmacokinetic and pharmacodynamic properties without causing visible side effects, and the drug may therefore be a useful antihistamine in equine medicine.     

Pharmacokinetics and effects of cetirizine in horses with insect bite hypersensitivity

Horses with insect bite hypersensitivity (IBH) have difficulty in completely avoiding allergens, so effective treatment options are required. A randomised, placebo controlled and double blinded field study was conducted to determine the pharmacokinetics and efficacy in reducing dermatitis of the antihistamine cetirizine given orally at 0.4 mg/kg twice daily for 3 weeks. The influence of protection blankets and stabling were also investigated.The estimated maximum plasma concentration (C_max) and trough plasma concentration of cetirizine were 135 ng/mL and 18 ng/mL, respectively. There was no difference in dermatitis reduction between the treatment and placebo groups (P = 0.77). The findings indicated that cetirizine was of no apparent benefit in treating IBH at the dose rate tested. The use of blankets and stabling were shown to have favourable influence on the dermatitis (P < 0.05) and may be the preferred options to prevent this condition.     

The Efficacy of Clemastine (Tavist), a Fatty Acid-containing Product (Derm Caps), and the Combination of Both Products in the Management of Canine Pruritus

Abstract— Thirty dogs having pruritus associated with atopy or idiopathy were treated with the HI-blocking antihistamine, clemastine (Tavist), a fatty acid-containing nutritional supplement (Derm Caps/Derm Caps ES), and both products simultaneously. Each product, and the combination of the two, were given for a two week period. Tavist and Derm Caps/Derm Caps ES each afforded satisfactory control of pruritus in 26.7 per cent of the dogs. The combination appeared to produce a synergistic effect in three dogs. Pruritus was satisfactorily controlled in 43.7 per cent of the dogs when Tavist and Derm Caps/Derm Caps ES were administered concomitantly. Résumé— Trente chiens souffrant de prurit associé soit à de l'atopie ou soit de causes indéterminées furent traités avec l'antihistaminique bloqueur H1, clémastine (Tavist), un supplément nutritionnel contenant des acides gras (Derm Caps ou Derm Caps ES) ainsi que les deux produits simultanément. Chaque produit ainsi que la combinaison des deux ont été donnés durant deux semaines et 26.7% des chiens ont démontré un contrôle satisfaisant du prurit avec soit le Tavist soit le Derm Caps/Derm Caps ES. L'utilisation des produits en combinaison semble avoir produit un effet synergique chez trois chiens. e prurit fut contrôlé de façon satisfaisante dans 43,7% des cas quand le Tavist et de Derm Caps. Derm Caps ES étaient administrés simultanément. Zusammenfassung— 30 Hunde mit Pruritus—durch Atopie oder idiopathisch bedingtwurden mit dem die H₁-Rezeptoren blockierenden Antihistaminikum Clemastin (Tavist), mit einem fettsäurehaltigen Futterzusatz (Derm Caps) und mit einer Kombination aus diesen beiden behandelt. Jedes dieser Produkte allein sowie beide zusammen wurden jeweils 2 Wochen gegeben. Tavist und Dermcaps alleine führten jeweils zu einer zufriedenstellenden Kontrolle des Pruritus in 26.7% der Fälle. Beide Produkte zusammen schienen einen synergistischen Effekt bei drei Tieren zu haben. Der Pruritus wurde mit der Kombination von Tavist und Derm Caps in 43.7% der Fälle zufriedenstellend kontrolliert. Resumen Treinta perros que padecían cuadros pruriginosos asociados a atopia canina o de origen idiopático se trataron con un antihistamínico bloqueador de los receptores H1, la clemastina (Tavist), con un suplemento nutricional que contenía ácidos grasos (Derm Caps) y con ambos productos simultáneamente. Cada producto y la combinación de ambos se administró durante un periodo de dos semanas de duración. El Tavist y Derm Caps consiguieron un control satisfactorio del prurito en el 26,7% de los casos. La combinación de ambos productos parecía producir un efecto sinergístico en 3 perros. El prurito se controló de forma satisfactoria en el 43,7% de los perros cuando se administraba concomitantemente el Tavist y el Derm Caps.