MICROBIOLOGY, PHARMACOKINETIC DISPOSITION AND SAFETY OF FLORFENICOL IN CATTLE

The minimum inhibitory concentration (MIC) and minimal bactericidal co ncentrations (MBC) of florfenicol were determined for isolates of Past eurella haemolytica and Pasteurella multocida obtained from animals wi th bovine respiratory disease (BRD). The MICs and MBCs of florfenicol against these important BRD pathogens were found to be remarkably simi lar. In a study involving the pharmacokinetic disposition and distribu tion of florfenicol, calves were given two doses of florfenicol (20 mg /kg) intramuscularly 48 hours apart. Serum, bronchial secretion (BS) a nd tissue cage fluid (TCF) concentrations were measured for 48 hours a fter the initial dose and for 60 hour;following the second dose. Florf enicol achieved excellent penetrations in both BS and TCF, and concent rations in BS were higher than those in serum, showing the affinity of florfenicol for lung tissue. Safety studies were performed in which c attle were given the commercial formulation of florfenicol (NUFLOR(R) Schering-Plough Animal Health(2)) at up to 10 times the recommended do se via intramuscular injection. Some side effects were associated with these higher dosages but were transient and reversible. NUFLOR(R) was well tolerated by cattle following intramuscular administration. The neck musculature was identified as the preferred site of administratio n.