Disposition kinetics of florfenicol in goats by using two analytical methods

Florfenicol, a monofluorinated analogue of thiamphenicol, has antibacterial activity against a broad spectrum of bacterial strains, including enteric bacteria that are resistant to chloramphenicol and thiamphenicol. The pharm acokinetics of florfenicol was studied following a single intravenous bolus or intramuscular injections at a dose of 20 mg/kg body weight, in five hea lthy goats. Serum florfenicol concentrations were determined using two anal ytical methods: microbiological assay and high-performance liquid chromatog raphy (HPLC). Pharmacokinetic analysis was performed using redundant routin e equations and the results derived from each method were compared. While f lorfenicol was detected for up to 4 and 8 h after administration by the bio assay, the drug was recovered in serum after 12 and 24 h by HPLC following intravenous and intramuscular injections, respectively. Comparison of the c oncentration profiles obtained by the two methods revealed substantial diff erences in the resultant kinetic data. Values for the initial serum concent ration, elimination half-life, the area under the serum concentration-time curve, the mean residence time, and the systemic bioavailability were signi ficantly (P<0.01) higher when florfenicol concentrations were determined us ing HPLC. In conclusion, differences between analytical methodologies shoul d be considered when interpreting the kinetic data for clinical use. Howeve r, both the hepatic biotransformations and the interchangeability of enanti omers need further investigation.