Pharmacokinetic parameters and optimal dosage of a florfenicol and tylosin mixture in beagle dogs

The aims of this study were to evaluate the in vitro antibacterial activity of a florfenicol and tylosin mixture and to determine the pharmacokinetic parameters of each drug following administration of the 2 : 1 florfenicol and tylosin mixture in beagle dogs. The antibacterial activity of the two antibiotics, both singly and as a mixture, was investigated in bacteria isolated from 119 beagle dogs. Minimum inhibitory concentrations were determined using the broth dilution method, whereas the checkerboard assay was used to evaluate the antibacterial effects of the combination of florfenicol and tylosin. The pharmacokinetic parameters of the two antibiotics were determined following administration of the mixture in beagle dogs. Serum concentrations of both drugs were analysed using high-performance liquid chromatography. Pharmacokinetics parameters such as area under the concentration-time curve, absolute bioavailability and systemic clearance were determined using non-compartmental analysis. The results showed that tylosin and florfenicol exerted varying degrees of antibacterial activity against the tested isolates. The combination of florfenicol and tylosin produced a synergistic and additive antibacterial effect. Analysis of the serum samples revealed a rapid and almost complete absorption of florfenicol and tylosin with mean bioavailabilities of 92.7% and 106.1%, respectively. The times needed to reach maximum concentration for florfenicol and tylosin were 1.5 and 3 h, respectively. Moreover, intramuscular injection of the mixture to beagle dogs resulted in serum concentrations that were higher than the corresponding minimum inhibitory concentrations in beagle dogs. This is the first study to report optimisation of florfenicol and tylosin doses following administration of a combination of the two drugs to beagle dogs.