Tissue distribution and residues of beta-lactam antibiotics in normal dairy cows.

Tissue residues and concentrations of benzylpenicillin, cloxacillin, ampicillin, amoxycillin, cephapirin, and cephacetrile were determined in normal dairy cows after parenteral administration of several forms of these drugs. Assay methods included the Sarcina lutea Kidney Test of Van Schothorst, the Bacillus subtilis BGA Tests at pH 6.0 and 8.0, the Escherichia coli Test and a Sarcina lutea Test performed at pH 8.0 of the agar, and specific quantitative assay methods. The E. coli test method demonstrated an insensitivity for the beta-lactam antibiotic residues. Identical results in residue testing of meat and kidney were obtained with the B. subtilis BGA tests and S. lutea test at pH 8.0, and these test methods replicated each other. The S. lutea Kidney Test was very often positive at times after treatment when the antibiotics were no longer detected in the meat. The qualitative and quantitative residue data from the renal cortex were higher than the data obtained from the muscle meat. The concentration relationship between renal cortex and muscle meat dependent on the formulation and type of drug used, and on the time of sampling after treatment. After treatment with products containing ampicillin trihydrate and procaine penicillin an unexpectedly long persistence of these drugs in the renal cortex was observed. It is suggested that, in the case of beta-lactam antibiotics, meat tests are more accurate indicators for the residue status of the carcass.