Florfenicol is a thiamphenicol derivative with the same mechanism of action as chloramphenicol (inhibition of protein synthesis). However, it is more active than either chloramphenicol or thiamphenicol, and may be more bactericidal than previously thought against some pathogens (e.g., BRD pathogens). Florfenicol has a broad spectrum of antibacterial activity that includes all organisms sensitive to chloramphenicol, gram-negative bacilli, gram-positive cocci, and other atypical bacteria such as mycoplasma. Florfenicol is highly lipophilic, which provides high enough concentrations to treat intracellular pathogens and cross some anatomic barriers (penetration across the blood–brain barrier in cattle is 46%). The half-life of florfenicol is 2-3 hours in cattle after IV administration, but it is prolonged (18 hours) after IM injection, and 27 hours after 40 mg/kg subcutaneously. In dogs, the half-life is shorter, with values of 1.1 and 1.2 after IV and oral administration, respectively. The half-life in cats is approximately 4 hours and 7.8 hours after IV and oral administration, respectively.
