Effectiveness of enrofloxacin in mastitis treatment after systemic administration in the isolated perfused sheep udder

C López-Cadenas1, N Fernández-Martínez1, M Sierra-Vega1, JM Gonzalo-Orden2, AM Sahagun-Prieto1, JJ García-Viéitez1. 1Universidad de León, Farmacología 24071, Spain, 2Universidad de León, Medicina y Cirugía 24071, Spain

Introduction: Although the intramammary administration remains the route of choice for the treatment of mastitis in sheep, the systemic route is becoming increasingly important. The use of both ways of administration simultaneously is likely to be advantageous in acute mastitis, since this produce maximum enrofloxacin concentration rapidly in all regions of the udder. The aim of this study was to determine the concentration of enrofloxacin in the glandular tissue after sytemic administration in the isolated perfused sheep udder and to compare these results with the minimum inhibitory concentration against some pathogen microorganisms causing mastitis in sheep (Staphylococcus aureus, Mycoplasma agalactiae, Escherichia coli, Streptococcus spp. and Pasteurella haemolytica).

Material and methods: Twelve healthy Assaf lactating sheep weighing 50 - 56 kg and aged 4 -5 years were used to carry out the study. Mammary glands taken at slaughter from these lactating sheeps were perfused in vitro with warmed and gassed Tyrode solution. After equilibration phase, the plasma concentrations of enrofloxacin following a single intravenous administration at a dose rate of 5 mg/kg body weight by the addition of enrofloxacin to the perfusión fluid (systemic treatment) were simulated. After 180 min, 5 g of glandular tissue was sampled at constant distances vertically from the teat (2, 4, 6, 8 cm). The concentration of enrofloxacin in glandular tissue was measured by HPLC with UV detection. The ratios of Cmax/MIC90 were calculated for Staphylococcus aureus, Mycoplasma agalactiae, Escherichia coli, Streptococcus spp. and Pasteurella haemolytica using the mean values of Cmax obtained in each sample taken. These data concern the inhibitory activity of enrofloxacin against some pathogen microorganisms causing mastitis in sheep.

Results and conclusions: After systemic administration of enrofloxacin to the perfusion fluid, mean enrofloxacin concentrations in glandular tissue were between 35.58 and 40.38 µg/g at all sites (2, 4, 6 and 8 cm distance from the teat base). Significant differences between the sampling sites were not found (ANOVA, p < 0.05). The tissue concentration was higher than the MIC90 (Cmax/MIC90 > 8) against some pathogen microorganisms causing mastitis in sheep: Staphylococcus aureus and Mycoplasma agalactiae (0.5 µg/mL), Escherichia coli and Streptococcus spp. (0.06 µg/mL) and Pasteurella haemolytica (0.03 µg/mL). Taking into account these results we can conclude that enrofloxacin, administered at 5 mg/kg body weight (systemic administration) could be used for treatment of mastitis caused by these microorganisms.