| Rifaximin is currently the only used for intestinal bacterial infections antibiotics rifamycin derivatives. Rifaximin was first approved in 1987 as an anti-infectious diarrhea drugs in Italy, was widely used in foreign countries after 2004, approved by the SFDA in our clinical application. Rifaximin is a broad spectrum that is effective against many Gram-positive and Gram-negative organisms, with good antimicrobial activity against a broad spectrum of bacterial species. Rifaximin has a low incidence of drug resistance, higher application security and efficiency, widely used for the intestinal tract caused by susceptible bacteria. To provide a reference in clinical application, the determination by HPLC, the antibacterial activities in vitro, pharmacodynamic and pharmacokinetics of rifaximin were studied in this paper.1 The determination of rifaximin by HPLCA method for determination of rifaximin by HPLC was established. The HPLC system consisted of C18 column (4.6 mm x 250 mm,5μm), the mobile phase of methanol-acetonitrile-0.075 mol/L potassium dihydrogen phosphate-l.Omol/L citric acid solution (volume ratio 50:20:25:5), UV The detection wavelength was 240 nm, injection volume was 20μL, the flow rate was 1.0 mL/min, column temperature was 30 ℃. The calibration curve was linear in the range of 0.04 mg/mL-0.16 mg/mL, regression formula were obtained through determination with HPLC method:A= 129674C-1402286, R2= 0.9995. The RSD of the variation coefficient was 0.47% within a run or 0.65% between runs, respectively. The RSD of stability rate was 0.89%. The RSD of repetition rate was 0.79%.The results showed that the method was simple, rapid, accurate and suitable for the content determination of rifaximin. The content of rifaximin in test solution is 99.08% compared with signed content 10%, the result accorded with the regulation of veterinary drug quality criterion.2 Study on the antibacterial activities of rifaximin in vitroTo study the antibacterial activity of rifaximin, ciprofloxacin, ceftriaxone, gentamicin, marbofloxacin against clinical strains and standard strains, an antimicrobial susceptibility testing was done by microdilution method.The results showed that rifaximin had very high activities to clinical strains and standard strains in vitro.The MIC of the rifaximin against S.aureu was 0.125 μg/mL, which was better than ciprofloxacin, ceftriaxone, gentamicin, marbofloxacin. Antibacterial activities of rifaximin in vitro against E.coli were weaker than ciprofloxacin, ceftriaxone, gentamicin, marbofloxacin. Antibacterial activities of rifaximin in vitro against Salmonella were similar with ciprofloxacin, marbofloxacin, weaker than ceftriaxone, gentamicin. The MIC of rifaximin in vitro against Proteus, Clostridium perfringens were similar with marbofloxacin, gentamicin, less than ciprofloxacin, ceftriaxone. Rifaximin have strong antibacterial activity in a variety of Gram-positive and Gram-negative bacteria.3 Study of rifaximin on the normal intestinal flora of broilers.The influence of rifaximin had on intestinal flora in normal broilers.5 day-old AA broilers in experiment groups were divided into 3 groups and rifaximin was administrated orally by 25,50,100 mg/kg in 3 continuous days. Chicken were killed at day 4,7,10 respectively after the first administraton and contents of the cecum and ileum were taken for selective culture, counting Lactobacillus and E. Coli, to evaluate the effectiveness of rifaximin on affecting number of intestinal flora in broilers. The results showed that the number of E. coli in all experiment groups decreased compared with the control group, high (100 mg/kg) dose group at day 4 after administration showed significant difference compared with control group, when no significant difference compared the other experiment groups. The Lactobacillus of ileum and cecum in all experiment groups increased compared with the control group, but the difference was not significant.4 Study on pharmacodynamics of rifaximin in chickens infected artificially by E.coliTherapeutic effect of rifaximin has been investigated in chickens infected artificially by E.coli. One hundred and eighty one-day old sanhuang broilers were randomly divided into six groups after 7 days breeding, three dose of rifaximin such as low(25 mg/kg), medium(50 mg/kg) and high dose groups(100 mg/kg), ciprofloxacin(1.25 g/mL), the healthy and infection control groups were designed. The results showed that rifaximin can effectively control the infection caused by E.coli at the dose of medium and high dose groups. The effective rates were 96.7% and 86.7%, respectively. The relative weight increase rates were 90.53% and 79.58% respectively. Rifaximin was used at the dose of high and medium can alleviate the symptom and prevent the discreasing weight and reduce the mortality rate of the broiler chicken infected by E.coli. The effect was superior to ciprofloxacin. All the results showed that the drug was perspective and recommend ability in the veterinary clinic. The commend at 50 mg/kg for chicken when used in clinic.5 Study on Pharmacokinetics of rifaximin in broiler chickensHPLC method to be established to determine the concentration in plasma of rifaximin in broiler chickens. Ten broiler chickens were used to give of rifaximin by single oral administration at a dose of 200 mg/kg. After extracted with ethyl acetate, rifaximin concentration of preparation samples were determined by HPLC/UV with solid phase extraction method. C18 was used as the reversed column, and methanol-acetonitrile-0.075 mol/L potassium dihydrogen phosphate-1.0 mol/L citric acid solution (volume ratio 50:20:25:5) as the mobile phase. The results suggested that, the standard curves for rifaximin was linar in a range of 0.25～25, R2= 0.9998, adding 0.5,5 and 25 rifaximin into blank plasma, the recovery rate were 88.17±0.02%,90.48±0.02%,97.97±0.03% respectively. The coefficient of within variation was 2.25%,2.02%,2.00%, the coefficient of between variation was 1.57%,3.47%,1.85% respectively. It was conclused that rifaximin by oral administration was almost not absorbed in broiler chickens, the concentration of plasma was very low. Rifaximin exist only in high concentrations in the animal gastrointestinal tract, mainly through fecal excretion. |
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