Abstract

Marbofloxacin is a second-generation fluoroquinolone with 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 the plasma pharmacokinetics of marbofloxacin alone and associated with dexamethasone to assess whether the pharmacokinetics of marbofloxacin is modified by dexamethasone in weaning calves. 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 dexamethasone. Treatments were exchanged after 2 weeks. Blood samples from each animal were collected in heparinized tubes at different times up to 24 hours, samples 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 in 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 were analyzed by PK Solution 2.0 software. Results indicate that intramuscular marbofloxacin has rapid absorption and distribution from the central compartment with moderate retention in body tissues. Statistical non-parametric Mann-Whitney test was used. It can be verified that the coadministration of dexamethasone did not significantly modify (P <0.05), the kinetic parameters of marbofloxacin.