[Pharmacokinetic aspects of mastitis therapy]

Treating mastitis in dairy cattle, most often antibiotics are used systemically or intracisternally, supported by influencing the inflammatory process with other measures. The success of systemic treatment is influenced by the bioavailability of the chemotherapeutic agent. Here, apart from the molecular size and protein binding, the fat-solubility of the active principle as well as its degree of ionisation play a major role. The degree of ionisation is determined by the isoelectric point (pKa) of the substance and by the pH-value of the surrounding medium. Thus, weak acids are mainly ionised in blood and cannot be transferred into udder tissue and milk. Weak bases react in the opposite way. Applied locally, the drug must not irritate the udder to secure deep diffusion into the glandular tissue. Therefore, topically administered drugs are formulated on an oily basis, also for longer prophylaxis during the dry-off-period. The pharmaceutic and pharmacokinetic relevance of the chemical and physical factors as well as the influence of the particle size of the active principle were demonstrated with benzylpenicillin potassium in the in vitro model of the isolated perfused bovine udder.