Plasma and pulmonary disposition of ceftiofur and its metabolites after intramuscular administration of ceftiofur crystalline free acid in weanling foals

The objectives of this study were to determine the plasma and pulmonary disposition of ceftiofur crystalline free acid (CCFA) in weanling foals and to compare the plasma pharmacokinetic profile of weanling foals to that of adult horses. A single dose of CCFA was administered intramuscularly to six weanling foals and six adult horses at a dose of 6.6 mg/kg of body weight. Concentrations of desfuroylceftiofur acetamide (DCA) were determined in the plasma of all animals, and in pulmonary epithelial lining fluid (PELF) and bronchoalveolar lavage (BAL) cells of foals. After intramuscular (IM) administration to foals, median time to maximum plasma and PELF concentrations was 24 h (12-48 h). Mean (+/-SD) peak DCA concentration in plasma (1.44 +/- 0.46 mu g/mL) was significantly higher than that in PELF (0.46 +/- 0.03 mu g/mL) and BAL cells (0.024 +/- 0.011 mu g/mL). Time above the therapeutic target of 0.2 mu g/mL was significantly longer in plasma (185 +/- 20 h) than in PELF (107 +/- 31 h). The concentration of DCA in BAL cells did not reach the therapeutic level. Adult horses had significantly lower peak plasma concentrations and area under the curve compared to foals. Based on the results of this study, CCFA administered IM at 6.6 mg/kg in weanling foals provided plasma and PELF concentrations above the therapeutic target of 0.2 mu g/mL for at least 4 days and would be expected to be an effective treatment for pneumonia caused by Streptococcus equi subsp. zooepidemicus at doses similar to the adult label.