Determination of Florfenicol and Doxcycline Residues in Chickens by Microbiological Assay

Background: Florfenicol (Ff) is a synthetic antibiotic with a broad antibacterial spectrum and high therapeutic effectiveness that was specifically developed for veterinary use as well as, doxcycline is an antibiotic synthetically derived from oxytetracycline. Methods: In the present study, the in-vitro efficacy of Ff and doxcycline against Salmonella entertidis and Escherichia coli (Serotype O78) pathogens was determined using disc diffusion technique and Minimum inhibitory concentrations (MICs). In the other hand serum and tissue residual levels of Ff and doxcycline after intramuscular (i.m.) administration of 30 mg/kg and 250 mg/kg orally respectively to 5 weeks old chicken were determined using microbiological assay method with Bacillus subtilis ATCC 6633 as a reference organism. Results: The results showed that both microorganisms were highly susceptible to Ff with lower MIC value than those of doxcycline. The peak concentration of florfenicol in serum was 5.34 ± 0.01 μg/ml and reached at 10 hr post medication and the drug was detected up to 48 hr while of doxcycline the peak concentration was 7.35±0.14 μg/ml at 12 hr post medication then declined gradually. Liver was the highest tissue concentration of florfenicol and the kidney was for doxcycline while muscle showed the lowest tissue concentration for both drugs. Conclusions: The results concluded that florfenicol was more effective in-vitro against the tested microorganisms as will as it persisted lower time than doxcycline in the tissue and sera of the chickens.