Treament Efficacy of Florfenicol and its Combinations Against E.coli in Chickens

A study was conducted on the antibacterial activity,post_antibiotic effect and efficacy of florfenicol and its combination with doxycycline against the experimental infection of chickens with E.coli.The results revealed that the minimal inhibitory concentrations(MICs)of flofenicol against E.coli were 1.6 mg·L~(-1),equal to that of chloramphenicol and 2.5% of thiamphenicol.The results also demonstrated that PAEs duration induced by florfenicol against E.coli (1.45～2.07 h) was much longer than that of thiamphenicol(P0.05) and showed concentration dependent.The sensitivity test for combination of florfenicol with doxycycline was conducted by Chess_boardmethod. The results illustrated that the combinations were indifferent to E.coli and fractional inhibitory concentration(FICs)was 1.5,that is to say,MICs of these combinations were 2 times lower than those of florfenicol alone.The PAEs of the combinations were little longer than those of singles against the same organism,and they illustrated indifference.Following treatment with three doses of florfenicol(10 mg·kg~(-1) and 20 mg·kg~(-1) via intramuscular,30 mg·kg~(-1) via oral )or two doses combinations (10 mg·kg~(-1) florfenicol plus 20 mg·kg~(-1) doxycycline or 20 mg·kg~(-1) florfenicol plus 40 mg·kg~(-1) doxycycline by oral ),the curative rates against E.coli were 73.3%,76.7%,73.3%,76.7% and 80.0%,respectively,and the mortality of infected control group was 80.0%.