Abstract
Florfenicol was administered intravenously and intramuscularly at a dose rate of 20 mg/kg bwt to determine its concentration in blood and bronchial secretions as well as kinetic behavior in healthy and diseased calves. Sever acute bronchopneumonia was induced via inoculating the animals with Pasteurella multocida. Following intravenous (i.v) administration, the serum concentration - time curve indicated a two compartment open model with a mean elimination half-lives (t 1/2β ) of 4.10 and 4.84 h in healthy and infected calves, respectively. The mean volumes of distribution at steady state (Vdss) were 0.68 and 0.63 L/kg and the total body clearances (Cltot) were 0.15 and 0.11 L/kg/h with mean residence time (MRT) of 0.05 and 0.05 h, respectively. Florfenicol was slowly eliminated from serum and bronchial secretions with elimination half-lives (t 1/2el ) of (12.43 and 17.23 h) and (13.74 and 22.46 h), respectively, following intramuscular (i.m.) injection. The peak concentrations (Cmax) in serum and bronchial secretions were (3.70 and 4.06 µg/ml) and (6.88 and 7.62 µg/ml) attained at (3.07 and 3.01 h) and (1.54 and 1.70 h), respectively. The drug is extensively distributed to bronchial secretions with AUCbronchial secretion / AUCserum ratio of 1: 2.53 and 1: 2.03, respectively. The clinical and hematological parameters in calves treated intramuscularly returned to normal faster than those treated intravenously. These results suggest that i.m. injection of florfenicol could be used for treatment of acute P. multocida bronchopneumonia in calves.
Highlights
Bronchopneumonia is one of the most economically important respiratory disorders affecting calves reared indoors [1,2]
The intrinsic antibacterial activity of the drug together with its pharmacokinetic properties after subcutaneous injection suggest that systemic florfenicol bronchopneumonia calves therapy should be explored, in field efficacy trials, as a means of eliminating P. haemolytica lung infections
The results of this study had shown that the serum and bronchial secretions concentrations of florfenicol in experimentally P. haemolytica-infected calves remained above the minimum inhibitory concentrations (MICs) for the most sensitive bacteria (P. multocida and P. haemolytica (0.25 to 1 μg/mL), and A. pleuropneumoniae (0.2 to 1.56 μg/mL) isolated from cattle [13,25] for 24 and 36 h post i.v. and i.m. injection
Summary
Bronchopneumonia is one of the most economically important respiratory disorders affecting calves reared indoors [1,2]. The etiology of calf bronchopneumonia is complicated and could involve viruses, Mycoplasmas, and bacteria [3]. Pasteurella species, play an important role in many outbreaks of calf bronchopneumonia. All Pasteurella species occur as commensals in the upper respiratory and alimentary tracts of their various hosts. They might increase the severity of the primary lung damage caused by viruses and exacerbate the clinical signs, frequently with fatal outcome (i.e. secondary to other infections). Varieties of some species, including P. multocida and / or P. haemolytica could act as primary pathogens and would produce sever acute pneumonia in calves [4,5,6,7]
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