Abstract

Marbofloxacin is second generation fluoroquinolone with bactericidal concentration dependent activity against Gram-negative, some Gram-positive and mycoplasma organisms due to the interaction with DNA gyrase enzyme. The study was conducted to determine plasma pharmacokinetics parameters in weaning calves after intramuscular administration of marbofloxacin and influence of flunixin co-administration. In a crossover design, each animal group A (n=3) received 6 mg / kg intramuscular marbofloxacin. Group B (n=3) received marbofloxacin 6 mg / kg plus 2.2 mg/ kg intramuscular flunixin meglumine. Treatments were exchanged after 2 weeks. Blood sample from each animal were collected in heparinized tubes at different times up to 24 hours post application, they were immediately centrifuged and stored at -20 °C until HPLC analysis. Preparative analyte assay consisted of liquid-liquid extraction using 200 microliters of plasma, 200 microliters of water, 800 microliters of methanol and enrofloxacin as internal standard, stirred 30” in vortex then centrifuged 30´ at 13,500 rpm at 4 °C. Separation and quantification were performed by isocratic elution on reverse phase, at 0.8 ml per minute flow rate, 50 microliter injection volume, pre- column, C-18 octadecylsilane column, fluorescence detector at 295 nm excitation and 490 nm emission and mobile phase composed of water, acetonitrile and triethylamine (79: 19: 1 v/v/v), pH 3. Plasma concentration data are analyzed by PK Solution 2.0 software. Results indicate that intramuscular marbofloxacin has rapid absorption and distribution from the central compartment, moderate retention in body tissues and wide, disseminating showing as well that the co-administration of flunixin does not modify the kinetics of marbofloxacin.