PHARMACOKINETIC ASPECTS OF MASTITIS THERAPY

Treating mastitis in dairy cattle, most often antibiotics are used sys temically or intracisternally, supported by influencing the inflammato ry process with other measures. The success of systemic treatment is i nfluenced 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 maj or role. The degree of ionisation is determined by the isoelectric poi nt (pKa) of the substance and by the pa-value of the surrounding mediu m. Thus, weak acids are mainly ionised in blood and cannot be transfer ed into udder tissue and milk. Weak bases react in the opposite way. A pplied locally, the drug must not irritate the udder to secure deep di ffusion into the glandular tissue. Therefore, topically administered d rugs are formulated on an oily basis, also for longer prophylaxis duri ng the dry-off-period. The pharmaceutic and pharmacokinetic relevance of the chemical and physical factors as well as the influence of the p article size of the active principle were demonstrated with benzylpeni cillin potassium in the in vitro model of the isolated perfused bovine udder.