A comparative study on irritation and residue aspects of five oxytetracycline formulations administered intramuscularly to calves, pigs and sheep

After intramuscular (IM) administration (dose 20 mg/kg) of three 20% (Terramycin/LA (product A), Alamycin LA (product B) and Terralon 20% LA (product C) and two 10% oxytetracycline (OTC) formulations (Engemycin 10% (product D) and Oxyject 10% (product E)), to calves, pigs and sheep, the OTC residue concentrations were determined in organs, muscle, fat, plasma, urine and at the injection sites at 10 days post injection (p.i.). At that time the irritation at the injection site was studied, too. The three 20%-formulations (products A, B, C) and one 10%-formulation (product E) induced considerable local irritation in and between the muscles. This was most pronounced in calves and pigs; in sheep the extent of irritation was limited. Ten days after administration of formulations A, B, C and E, OTC residues were found in organs and the OTC recovery at the injection sites varied widely among the three species. Following IM injection of product D minimal tissue irritation and no OTC residues could be detected at the injection site at 10 days p.i. The differences in local tissue irritation and the residue state of the carcass (including injection site) are related to the various solvent systems used in the formulations.