Pharmaceutical and pharmacological remarks upon using dry-off preparations in dairy cows

In an earlier study, the isolated perfused bovine udder was used to study the pharmacokinetics of two antibiotic long acting drugs called dry-off preparations. During three hours of diffusion, high pressure liquid chromatography showed that with micronized active principles (particle size 4.5 mum in average) and suitable ointment base, but contrary to 23 mum large particles, a rapid accumulation in the entire glandular tissue above minimal inhibitory concentrations can be reached without an undesirable rapid absorption into the blood. Therefore, dry-off preparations authorized in Germany were now examined microscopically with regard to the particle size of included antibiotics. The particles sizes ranged between 0.3 and 112 mum. in several preparations, the number of orders of magnitude, which the particles were allocated to, exceeded the number of different active principles or molecular formulations of the same active principle. Thus, the size homogeneity and micronisation of the particles was independent of the active principle components. These dissimilar, especially the > 10 mum large particles may cause problems with respect to a sufficient tissue distribution as has been demonstrated with the described pharmacokinetic in vitro studies.