Cefadroxil in the horse: pharmacokinetics and in vitro antibacterial activity

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Abstract
Wilson, W.D., Baggot, J.D., Adamson, P.J.W., Hirsh, D.C. & Hietala, S.K. Cefadroxil in the horse: pharmacokinetics and in vitro antibacterial activity. J. vet. Pharmacol. Therap. 8, 246–253.Sodium cefadroxil was administered as a single intravenous dose (25 mg/kg) to six healthy adult mares. Plasma samples were collected over a 24‐h period and cefadroxil concentrations were measured by microbiological assay. The pharmacokinetic behavior of the drug was appropriately described in terms of a one‐compartment open model. Values for the major pharmacokinetic terms were: extrapolated initial plasma concentration = 59.2 ± 15.0 μg/ml; half‐life = 46 ± 20 min; apparent volume of distribution = 462 ± 191 ml/kg; and body clearance = 7.0 ± 0.6 ml/min.kg. In a subsequent study, a suspension of cefadroxil monohydrate was administered intragastrically (25 mg/kg) to the same six horses. Plasma concentrations of the drug peaked at 1–2 h but, in general, absorption was both poor and inconsistent. The data were unsuitable for determination of cefadroxil bioavailability from this oral dosage form.Ninety‐nine isolates of eleven bacterial species obtained from clinically ill horses were tested for susceptibility to cefadroxil. All strains of Streptococcus equi, Streptococcus zooepidemicus, coagulase‐positive staphylococci, Corynebciclerium pseudotuberculosis and five out of six strains of Actinobacillus suis were highly susceptible to the drug (MIC 128 μg/ml). Dr W. Dcvid Wilson, Department of Medicine, School of Veterinary Medicine, Universily of California, Davis, CA 95616, U.S.A.