In vivo synergistic antimicrobial effects against pathogens in chickens have been reported for florfenicol (FF) and thiamphenicol (TAP) at a ratio of 1:2. The present study evaluates the pharmacokinetics and tissue residues of a single combined intramuscular treatment of FF+TAP at 1/6 and 1/3 of their respective recommended doses in 5-week old broiler chickens. The drug concentrations were determined by LC/MS/MS. Significant reductions were observed in the Cmax (0.045 and 2.64 µg/mL for FF and TAP, respectively) and AUC (0.13 and 7.19 h•µg/mL for FF and TAP, respectively) compared to corresponding values reported for the recommended dose (up to two orders of magnitude lower). Tissue FF (10.6-88.4 µg/kg) and TAP concentrations (6.5-147.0 µg/kg) declined below the maximum residue limit within only one day except for TAP residue in skin/fat. This experiment provided supporting evidence for a complete study that synergistic FFTAP has potential benefits over monotherapy since drug residues could be greatly reduced; much shorter withdrawal period was strongly indicated. [ABSTRACT FROM AUTHOR
