Abstract

The rabbit as a model for the investigation of the bioavailablity of intramuscularly administered veterinary drugs is described. The bioavailabilities of ampicillin from two products, which had been found to be different in calves, were investigated. The pharmacokinetics of ampicillin in the rabbit after intravenous administration can be described by an open two-compartment model. The elimination halflife of ampicillin in the rabbit is about 45 min. A large difference between male and female rabbits was observed in the apparent volume of distribution (0.26 l/kg and 0.13 l/kg resp.) and the total body clearance (1.07 l/kg and 0.60 l/kg.h.). In a two- way cross-over design the bioavailabilities of two intramuscular ampicillin products (Ampikel and Albipen) were compared. The ampicillin levels in plasma, the plasma creatin kinase activity and the tissue damage in the injection sites were estimated. The absolute bioavailabilities from both products were 100% and 40% for Ampikel and Albipen respectively. Differences in pharmacokinetics of ampicillin between sexes was also observed after intramuscular administration. After intramuscular administration of these products only slight tissue damage could be detected in the injection sites. Further investigations with other intramuscular drugs are necessary to validate this model.