Determination of plasma and skin concentrations of orbifloxacin in dogs with clinically normal skin and dogs with pyoderma

Plasma and skin concentrations of orbifloxacin (Orbax tablets, Schering-Plough Animal Health) were assessed in 14 clinically normal dogs and 14 dogs with pyoderma following oral administration of the drug at 7.5 mg/kg once daily for 5 to 7 days. Skin biopsies and whole blood samples were obtained before dosing and at the time of the expected maximum concentration in skin (3 hours after dosing) on the first and on the fifth to seventh day of dosing. Skin biopsies and plasma were analyzed for orbifloxacin concentrations by high-performance liquid chromatography. Dogs with pyoderma had significantly higher mean skin concentrations of orbifloxacin within 3 hours of administration (Day 0: 7.80 +/- 3.40 mcg/g, Days 4 to 6: 9.47 +/- 6.23 mcg/g) than did dogs with normal skin (Day 0: 3.85 +/- 1.08 mcg/g, Days 4 to 6: 5.43 +/- 1.02 mcg/g). After dosing on Day 0 and after five to seven daily treatments, dogs with pyoderma had significantly higher mean orbifloxacin skin:plasma ratios (1.40 and 1.44, respectively) than did clinically normal dogs (0.81 and 0.96, respectively). The accumulation of orbifloxacin in diseased skin may contribute to the efficacy of this compound for the treatment of bacterial skin infections.