Abstract: The pharmacodynamics of florfenicol on bacterium Yersinia ruckeri were studied in vitro including minimal inhibitory concentration(MIC);minimal bactericidal concentration(MBC ); the growth curve of the bacterium; the bacteriocidal curve of the florfenicol and post-antibiotic effect(PAE). The results showed thatthe florfenicol had MIC of 0.5 μg·mL^-1, MBC of 1μg·mL^-1 and MBC/MIC of 2. The logarithmic growth phase was observed in the bacterium cultured in fluid medium for 1 hour and lasted about 7 hours. The florfenicol showed the maximum activity 4-6 hours after administration and was a dose-dependence by the bacteriocidal curve. The value of PAE were found to be 3.71±0.11 in 2 MIC,4.54± 0.27 in 4 MIC, and 5.52± 0.23 in 8 MIC. Florfenicol had the most effective inhibition of Y. ruckeri at pH 6-8. There was no significant impact of Mg2+, serum content, and less than 108 of bacteria quantity on bactericidal activity of the florfenicol. Therefore, the maximal efficacy of florfenicol depends on dose, administration period and the optimal environmental factors.

Key words: florfenicol, Yersinia ruckeri, pharmacodynamics in vitro