Pharmacokinetics in plasma and alveolar regions of healthy calves subcutaneously administered a single dose of enrofloxacin

This study aimed to analyze the pharmacokinetics of enrofloxacin (ERFX) and its metabolite ciprofloxacin (CPFX) in plasma, as well as their migration to, and retention in, the epithelial lining fluid (ELF) and alveolar cells within the bronchoalveolar fluid (BALF). Four healthy calves were subcutaneously administered a single dose of ERFX (5 mg/kg). ERFX and CPFX dynamics post-administration were analyzed via a non-compartment model, including the absorption phase. The Cmax of plasma ERFX was 1.6 +/- 0.4 mu g/ml at 2.3 +/- 0.5 hr post-administration and gradually decreased to 0.14 +/- 0.03 mu g/ml at 24 hr following administration. The mean residence time between 0 and 24 hr (MRT0-24) in plasma was 6.9 +/- 1.0 hr. ERFX concentrations in ELF and alveolar cells peaked at 3.0 +/- 2.0 hr and 4.0 +/- 2.3 hr following administration, respectively, and gradually decreased to 0.9 +/- 0.8 mu g/ml and 0.8 +/- 0.5 mu g/ml thereafter. The plasma half-life (t1/2) of ERFX was 6.5 +/- 0.7 hr, while that in ELF and alveolar cells was 6.5 +/- 3.6 and 7.4 +/- 4.3 hr, respectively. The Cmax and the area under the concentration-time curve for 0-24 hr for ERFX were significantly higher in alveolar cells than in plasma (P<0.05). These results suggest that ERFX is distributed at high concentrations in ELF and is retained at high concentrations in alveolar cells after 24 hr in the BALF region; hence, ERFX may be an effective therapeutic agent against pneumonia.