Time course of enrofloxacin and its active metabolite in peripheral leukocytes of dogs.

The accumulation of fluoroquinolones in peripheral leukocytes is well established for several members of this family of drugs. This study documented accumulation of enrofloxacin and its active metabolite, ciprofloxacin, in canine peripheral leukocytes after oral administration at 7.5, 10, or 20 mg/kg, doses that are within the currently approved label of Baytril (Bayer Corporation Animal Health, Shawnee Mission, KS) in the United States. Accumulation index, as defined by C(max) in white blood cells (WBCs) divided by C(max) in plasma at the same time points, ranged from 47-fold to 63-fold for enrofloxacin and 28- to 35-fold for ciprofloxacin. Time course of both enrofloxacin and ciprofloxacin in WBCs paralleled the time course in plasma. Disappearance half-life of ciprofloxacin from WBCs was significantly (P = .001) longer than was enrofloxacin (P= .015) for all doses studied. The accumulation of enrofloxacin in peripheral leukocytes may contribute to the antimicrobial efficacy of this compound.