Ciprofloxacin Pharmacokinetics in Clinical Canine Patients

BACKGROUND Ciprofloxacin generic tablets approved for human use frequently are administered to dogs for treatment of bacterial infections because they are inexpensive and readily available. However, previous work indicated low and variable oral absorption in healthy research dogs. OBJECTIVE To examine orally administered ciprofloxacin in a group of clinical canine patients using population pharmacokinetics in order to identify minimum inhibitory concentrations (MIC) that potentially could be achieved with orally administered ciprofloxacin in dogs. ANIMALS Thirty-four clinical canine patients; mean weight, 22.95 kg (range, 4.6-57 kg). METHODS Ciprofloxacin generic tablets intended for human use were administered to dogs in a prospective study (mean dose, 23.5 mg/kg). Sparse blood sampling was used to obtain population pharmacokinetic results with nonlinear mixed-effects modeling. These data were used to estimate a breakpoint for susceptible bacteria. Monte Carlo simulations were used to determine the probability of target attainment (PTA) for an area under the curve (AUC)/MIC ratio of ≥100, the pharmacokinetic-pharmacodynamic target for fluoroquinolones. RESULTS The values for volume of distribution, peak concentration, and half-life were 10.7 L/kg (11.7%), 1.9 μg/mL (11.66%), and 4.35 hours (7.62%), respectively (mean, % coefficient of variation [CV]). The size of the dog was an important covariate with larger dogs achieving lower plasma drug concentrations than smaller dogs, despite a similar mg/kg dose. Ninety percent PTA was obtained for a MIC ≤ 0.06 μg/mL. CONCLUSIONS AND CLINICAL IMPORTANCE A breakpoint (susceptible) of ≤0.06 μg/mL should be considered when ciprofloxacin tablets are administered to dogs at a dose of 25 mg/kg once daily, which is much lower than the breakpoint of ≤1 μg/mL in humans.