Plasma concentrations of enrofloxacin and its active metabolite ciprofloxacin in dogs following single oral administration of enrofloxacin at 7.5, 10, or 20 mg/kg.

Plasma concentrations of enrofloxacin and its active metabolite ciprofloxacin were monitored following oral administration of enrofloxacin at 7.5, 10, and 20 mg/kg to six healthy female bloodhounds using a randomized crossover design. Plasma samples were collected at various times over 24 hours following drug administration. Both the parent drug and its metabolite were detected by high-performance liquid chromatography, and plasma drug concentration-versus-time curves were subjected to noncompartmental pharmacokinetic analysis. Descriptive statistics were determined for each dosage, and comparisons were made among dosage groups for selected pharmacokinetic parameters. Increasing dosages of enrofloxacin resulted in increased plasma concentrations of both enrofloxacin and ciprofloxacin. Maximum concentration (Cmax) was 2.12 +/- 0.59, 2.1 +/- 0.34, and 4.74 +/- 1.05 mcg/ml for enrofloxacin and 1.30 +/- 0.31, 1.30 +/- 0.32, and 1.86 +/- 0.35 mcg/ml for ciprofloxacin when enrofloxacin was given at dosages of 7.5, 10, and 20 mg/kg, respectively. Cmax and area under the curve (AUC) for both enrofloxacin and ciprofloxacin were significantly greater at 20 mg/kg than at 7.5 and 10 mg/kg. Disappearance half-life was similar for all dosages, ranging from 4.6 to 5.2 hours for enrofloxacin and 8.8 to 10.7 hours for ciprofloxacin. Ciprofloxacin contributed up to 42% of the Cmax and up to 55% of the AUC of the total (enrofloxacin plus ciprofloxacin). For organisms with a minimum inhibitory concentration (MIC) of 0.5 mcg enrofloxacin/ml, an inhibitory quotient (IQ; Cmax:MIC) of 8 or more was achieved in plasma only at 20 mg/kg.