Florfenicol, the active substance of Florox, is a thiamphenicol derivative where the hydroxyl group is substituted with fluorine. Florfenicol has a bacteriostatic activity: it binds with the 70S ribosomal subunit in the bacterial cell protoplasm, thus blocking peptidyl transferase, which leads to the inhibition of protein synthesis performed by ribosomes of the sensitive microbial cell. Florfenicol is effective against acetyl transferase-producing bacteria resistant to chloramphenicol. Florfenicol has a wide range of antibacterial activity against Staphylococcus spp., Streptococcus spp., Escherichia coli, Actinobacillus pleuropneumoniae, Pasteurella spp., Bordetella bronchiseptica, Haemophilus spp., Fusobacterium necrophorum, Klebsiella pneumoniae, as well as mycoplasma M. hyopneumoniae и M. hyorhinis. After parenteral administration, florfenicol is quickly absorbed and distributed among most organs and tissues of the animal. It reaches its peak serum concentration after 30-90 minutes and remains at the therapeutic level for at least 48 hours. Florfenicol is eliminated unchanged as metabolites mostly with urine and partially with feces.