Study On Subacute Toxicity, Residue And Elimination Of Azithromycin In Broilers

Azithomycin, a 15-membered-ring macrolide, is the first of a class of antibiotics classified as azalides that differ structurally from other macrolides by the insertion of a methyl-substituted nitrogen atom at position 9a in the lactone ring. This structurally modification produces a significant increase in potency against Gram-negative bacteria in comparison with erythromycin, with the retention of the classical activity against Gram-positive bacteria. The present study was to determine that azithromycin has increased stability at an acid pH, a longer half-life, a more extensive distribution, a slower elimination than other macrolides, and the ability to achieve high tissue concentrations by direct uptake and delivery via phagocytes. Furthermore the side-effects are less than erythromycin and roxithromycin.After comfirmed preferred antimicrobial to prevent severe acute respiratory syndrome (SARS) by ministry of health the people's republic of China in 2003, azithomycin was embodied by the provincial veterinary drug standard and the applied effectiveness of clinic of veterinarian is perfectness. The patent protection of azithomycin was over Oct.25 in 2005, but the studies of azithomycin in feeding animal still don't develop across-the-board in the internal.The overseas numerous studies have reported its growth promotion effect in livestock, and it is possible for azithomycin to be used safely and effectively in poultry. As a new veterinary medicine for food producing animals, the veterinary drug residues is a key parameter to evaluate the veterinary clinical application, while residue elimination is the scientific groundwork to avoid drug residue. So in the research, systemic studies have been carried out following the requirments of clinical evaluation in new drug research, which focuse on the subacute toxicity, pathology, effectiveness in vitro, analytical methods of residues and residue elimination of azithomycin in Mahua broilers. The results clarified the effectiveness and safety of azithomycin in broilers, and indicated that azithomycin has a good application foreground in poutry production.1. The antimicrobial susceptibility test of azithromycin on veterinary clinical pathogenic microbes in vitroThe in vitro antibacterial activities of azithromycin on familiar veterinary clinical pathogenic microbes in broiler was tested by micro-dilution method. The results showed that azithromycin was active to Mycplasma gallisepticum, Staphylococcus auerus and Escherichia coli.. The minimal inhibitory concentration (MIC) is 0.125,0.5,1.0μg/ml, and the minimal bactericidal concentration (MBC) is 0.5,16,2.0μg/ml. The results also showed that the antibacterial activity of azithromycin on Mycplasma gallisepticum and Escherichia coli. was stronger than that of erythromycin thiocyanate, while on Staphylococcus auerus was weaker than that of erythromycin thiocyanate. But the bactericidal activity of azithromycin is comparative strong, so this indicated that azithromycin could be used as an antibacterial agent clinically.2. Study on subacute toxicity of azithromycin and pathology in Mahua broilersEighty 19-days-old Mahua broilers were divided randomly into four groups and the 4 groups were given 0, 50, 100 and 200 mg/L azithromycin by freely drinking for 14 days. Growth rate and feed conversion rate in 50 mg/L group were significantly higher than that in the other groups (P<0.05). The activity of alanine transaminase (ALT) and liver coefficient in 200 mg/L group increased significantly compared with that in control group and 50 mg/L group (P<0.01). Livers of chickens in 200 mg/L group becames wollen, yellow and fragile and appeared necrotic focus, and gallbladder was intumescent and filled with gall. Disordered distribution, vacuolar plasms and diffuse fatty degeneration were observed in liver cells in the 200 mg/L group. The results showed that growth rate of broilers was promoted by 50mg/L azithromycin but inhibited by azithromycin over 100 mg/L.3. Detection of azithromycin residues in broiler tissues by HPLCA highly sensitive specific method for determination of residues of azithromycin in broiler tissues by reverse-phase high-liquid chromat- bgramphy was developed and validated. Separation was achieved on a C₁₈ (4.6mm×250mm,5μm) at UV 210nm with the mobile phase of acetonitrile-lsopropylalcohol-0.002 mol/L phosphate (60:15:25,v/v/v). Samples were extracted using chloroform/lsopropylalcohol(95:5, v/v). The results was showed that a good linear relationship was obtained in the concentration range of 0.05-5.0μg/g (r>0.990). The limit of determination in serum was 0.02μg/ml and the limits of quantitation were 0.05μg/g. The average recovery was above 83% in serum and above 77% in tissues. The relative standard deviation of intra- and inter-day were less than 5%. In a word the method is quick, accurate, and repeat, and is accorded with the requirement for determining residues of azithromycin in broilers.4. Study on residue elimination of azithromycin after multiple-dose oral administration in broilersAzithromycin was administrated to Mahua broilers in medicated menstruum with 10 mg/kg body weight once daily for seven consecutive days, then HPLC-UV method was used to determine the concentrations of azithromycin in tissues. The results showed that the residue levels of azithromycin in broilers from high to low were liver, kidney, spleen, muscle and serum. In this study, all concentrations of azithromycin in various tissues frequently exceeded those in serum by 10-40 times. After 11 days, the concentrations of azithromycin in various tissues were under the limits of quantitation. Refering to the minimal risk levels (MRLs) of erythromycin in broilers, the drug withdrawal should be preponderated over 15 days.In conclusion, following the clinical evaluation procedure in newresearch, this study opens out the good application foreground, determines the safe dose and reasonable dose of azithomycin in broilers, and clarifies the residue elimination characteristics, and establishes the withdrawal time of azithomycin in boilers. Moreover the feasible analytical methods of azithomycin are developed to control the redsidues of azithomycin. These results will submit the referenced data for the effectiveness and safety evaluation of azithomycin in poutry, and give the scientific guidances for the reasonable use of azithomycin in the veterinary clinic. As a conclusion azithomycin is safer than erythromycin with excellent growth promotion effect and antimicrobial activity, and it is promising for azithomycin to be used extensively in poutry production.