PHARMACOKINETICS OF FLORFENICOL FOLLOWING INTRAVENOUS AND INTRAMUSCULAR DOSES TO CATTLE

The disposition of florfenicol after single intravenous and intramuscu lar doses of 20 mg of florfenicol/kg of body weight (b.w.) to feeder c alves was investigated. Serum florfenicol concentrations were determin ed by a sensitive high performance liquid chromatographic method with a limit of quantitation of 0.025 mug/ml. The extent of serum protein b inding of florfenicol was only 13.2% at a serum florfenicol concentrat ion of 3.0 mug/ml. Serum concentration-time data after intravenous adm inistration were best described by a triexponential equation. Total bo dy clearance and steady state volume of distribution were 3.75 ml/min/ kg b.w. and 761 ml/kg b.w., respectively. The terminal half-life after intravenous administration was 159 min. The absolute systemic availab ility after intramuscular administration was 78.5% (range: 59.3-106%) and the harmonic mean of the terminal half-life was 1098 minutes, indi cating slow release of the florfenicol from the formulation at the int ramuscular injection site.