Pharmacokinetics of selamectin following intravenous, oral and topical administration in cats and dogs

Authors: Sarasola, P.¹; Jernigan, A. D.²; Walker, D. K.³; Castledine, J.¹; Smith, D. G.¹; Rowan, T. G.¹

Source: Journal of Veterinary Pharmacology & Therapeutics, Volume 25, Number 4, August 2002 , pp. 265-272(8)

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Abstract:

Pharmacokinetics of selamectin following intravenous, oral and topical administration in cats and dogs. J. vet. Pharmacol. Therap.24, 265-272.

The pharmacokinetics of selamectin were evaluated in cats and dogs, following intravenous (0.05, 0.1 and 0.2 mg/kg), topical (24 mg/kg) and oral (24 mg/kg) administration. Following selamectin administration, serial blood samples were collected and plasma concentrations were determined by high performance liquid chromatography (HPLC). After intravenous administration of selamectin to cats and dogs, the mean maximum plasma concentrations and area under the concentration-time curve (AUC) were linearly related to the dose, and mean systemic clearance (Cl_b) and steady-state volume of distribution (V_d(ss)) were independent of dose. Plasma concentrations after intravenous administration declined polyexponentially in cats and biphasically in dogs, with mean terminal phase half-lives (t_½) of approximately 69 h in cats and 14 h in dogs. In cats, overall Cl_b was 0.470 ± 0.039 mL/min/kg (±SD) and overall V_d(ss) was 2.19 ± 0.05 L/kg, compared with values of 1.18 ± 0.31 mL/min/kg and 1.24 ± 0.26 L/kg, respectively, in dogs. After topical administration, the mean C_max in cats was 5513 ± 2173 ng/mL reached at a time (T_max) of 15 ± 12 h postadministration; in dogs, C_max was 86.5 ± 34.0 ng/mL at T_max of 72 ± 48 h. Bioavailability was 74% in cats and 4.4% in dogs. Following oral administration to cats, mean C_max was 11929 ± 5922 ng/mL at T_max of 7 ± 6 h and bioavailability was 109%. In dogs, mean C_max was 7630 ± 3140 ng/mL at T_max of 8 ± 5 h and bioavailability was 62%. There were no selamectin-related adverse effects and no sex differences in pharmacokinetic parameters. Linearity was established in cats and dogs for plasma concentrations up to 874 and 636 ng/mL, respectively. Pharmacokinetic evaluations for selamectin following intravenous administration indicated a slower elimination from the central compartment in cats than in dogs. This was reflected in slower clearance and longer t_½ in cats, probably as a result of species-related differences in metabolism and excretion. Inter-species differences in pharmacokinetic profiles were also observed following topical administration where differences in transdermal flux rates may have contributed to the overall differences in systemic bioavailability.

Document Type: Research article

DOI: http://dx.doi.org/10.1046/j.1365-2885.2002.00415.x

Affiliations: 1: Veterinary Medicine Clinical Development, Pfizer Animal Health Group, Pfizer Ltd, Sandwich, Kent, UK, 2: Veterinary Medicine Clinical Development, Pfizer Animal Health Group, Pfizer Inc., Groton, CT, USA, 3: Department of Drug Metabolism, Pfizer Global Research and Development, Pfizer Ltd, Sandwich, Kent, UK,

Publication date: 2002-08-01

Pharmacokinetics of selamectin following intravenous, oral and topical administration in cats and dogs

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