Tissue distribution of cloxacillin after intramammary administration in the isolated perfused bovine udder

Mammary glands taken at slaughter from healthy lactating cows were perfused in vitro with warmed and gassed Tyrode solution. 600 mg cloxacillin benzathine were administered as Orbenin Extra Dry Cow by the intramammary route to six front and rear quarters each. Samples of glandular tissue - at different distances from and vertical to the teat right up to the udder base - were gathered from the treated quarters after 6 h. Perfusate was also sampled before and hourly after treatment for 6 h. The cloxacillin content of the tissue samples and perfusate samples was analysed by high performance liquid chromatography.The concentration of cloxacillin in the glandular tissue of front quarters measured 6 h after administration tended to decrease with increasing vertical distance from the teat. The decrease pattern of the concentration was not quite clear in rear quarters. A considerable variation in the tissue concentrations of cloxacillin was obvious, which reflects in vivo conditions. The concentrations measured in the perfusate samples were below the limit of quantification at all time points, indicating limited absorption of the antibiotic from the glandular tissue.After intramammary administration of the dry off product containing cloxacillin benzathine concentrations of more than 0.5 μg/g (MIC) were reached in all regions of the front and rear quarters.Various cloxacillin benzathine containing intramammary suspensions are registered for use in cattle as antibiotics for intramammary use at drying off. The drying off formulations are recommended for routine use in cows at drying off to treat existing intramammary infections and to provide prolonged protection against new infections during the dry period.Cloxacillin is known as an effective agent against penicillin-resistant and sensitive staphylococci (Staphylococcus aureus), the most prevalent Gram positive pathogen involved in persistent udder infections, which are targeted by the drying off treatment. In a recent pan-Eu