Pharmacokinetics and tissue depletion of florfenicol in Leghorn and Taiwan Native chickens

Chang, S. K., Davis, J. L., Cheng, C. N., Shien, R. H., Hsieh, M. K., Koh, B. W., Chou, C. C. Pharmacokinetics and tissue depletion of florfenicol in Leghorn and Taiwan Native chickens. J. vet. Pharmacol. Therap. 33 , 471–479. Florfenicol (Ff) is a synthetic antibiotic with a broad antibacterial spectrum and high therapeutic effectiveness that was specifically developed for veterinary use. In the present study, tissue residual levels and the pharmacokinetics of Ff after oral administration of 30 mg/kg to Leghorn and Taiwan Native chicken were studied. Furthermore, differential pharmacokinetics between leg and breast muscles were compared using samples collected from an optimized microdialysis model designed for avian species. Significant differences in C_max were detected between the plasma and muscle microdialysates, and between the breast and leg microdialysates of the Leghorn chickens by noncompartmental pharmacokinetic analysis. After a single oral dose of Ff at 30 mg/kg, the drug was quickly absorbed and widely distributed with tissue penetration factors significantly different between leg and breast muscles. The serum protein binding of Ff was estimated to be 16.8 ± 1.2%. Significant breed differences in tissue depletion were noted and characterized by higher Ff concentration in the brain, lung, kidney and at least 12 h longer resident times in kidney, heart and spleen for Taiwan Native chicken. Results from this investigation demonstrate the practicality of using in vivo microdialysis in chickens for pharmacokinetic studies and reveal significant time‐dependent differences in the free concentrations of Ff in leg and breast muscles. The tissue depletion study signified breed differences in tissue residue concentration and detection times between Leghorn and Taiwan Native chickens. Therefore, currently used withdrawal times for Ff in chickens can not be assumed safe for Taiwan Native chickens.