Tissue distribution of enrofloxacin after intramammary and systemic administration in the isolated perfused sheep udder.

JJ García-Viéitez1, C López-Cadenas1, JM Rodriguez-Lago1, JF Garcia-Sierra2, FJ Rodriguez-Lera2, MJ Diez-Liébana1. 1Universidad de León, Farmacología 24071, Spain, 2Universidad de León, Arquitectura y Tecnologia de Computadores 24071, Spain

Introduction: Insufficient contact between drug and causative bacteria at the site of infection is a major cause of mastitis treatment failure. Drugs and routes of administration that achieve high concentration at the site of infection are needed to provide an adequate treatment. The aim of this study was to determine the concentration of enrofloxacin in the glandular tissue after intramammary and sytemic administration in the isolated perfused sheep udder.

Material and methods: Twenty-six healthy Assaf lactating sheep (50 – 56 kg and 4 – 5 years) were used to carry out the study. Mammary glands taken at slaughter from these lactating sheep were perfused in vitro with warmed and gassed Tyrode solution. Intramammary treatment: After equilibration phase, one intramammary syringe of enrofloxacin (1 g enrofloxacin per 5 g ointment) was administered via the teat canal and massaged into the glandular cistern. Systemic treatment: the plasma concentrations of enrofloxacin following a single intravenous administration at a dose rate of 5 mg/kg body weight was simulated by the addition of enrofloxacin to the perfusión fluid. In both cases and after 180 min, 5 g of glandular tissue was sampled at constant distances vertically from the teat base (2, 4, 6, 8 cm) using a scalpel. The concentration of enrofloxacin in glandular tissue was measured by HPLC with UV detection.

Results and conclusions: After intramammary administration, the concentration of enrofloxacin in the glandular tissue decreased exponentially with increasing vertical distance from the teat base. Mean enrofloxacin concentration at 2 cm was 123.80 µg/g; at 4 cm was 54.48 µg/g; at 6 cm was 36.72 µg/g, and at 8 cm was 26.42 µg/g tissue. In the case of the systemic administration of enrofloxacin to the perfusion fluid, mean enrofloxacin concentrations in glandular tissue was 35.58 µg/g; at 4 cm was 36.45 µg/g; at 6 cm was 40,38 µg/g, and at 8 cm was 39.97 µg/g tissue. We can conclude that the tissue concentrations of enrofloxacin achieved after intramammary administration were higher than those reached after systemic administration in biopsies taken at 2 cm and slightly higher at 4 cm from the teat base. However, at the base of the breast (6 and 8 cm) the tissue concentration achieved after intramammary administration were slightly lower than those obtained after systemic administration. The use of both routes of administration simultaneously is likely to be advantageous in acute mastitis, since this produces maximum enrofloxacin concentrations rapidly in all regions of the udder.