Tissue distribution and residues of aminoglycoside antibiotics in normal dairy cows.

The concentration and persistence of streptomycin, dihydostreptomycin (DHS), neomycin, and kanamycin in the body organs of normal dairy cows following intravenous (i.v.) and intramuscular (i.m.) injections were determined by qualitative and quantitative assay methods. The most sensitive qualitative procedure, i.e. Bacillus subtilis BGA at pH 8.0, failed to detect kanamycin in the meat of cows slaughtered 4 hours after i.m. and 6 hours after i.v. injections. This test, however, was positive for the kidneys of cows slaughtered 144 hours after the i.m. administration of neomycin. Low concentrations of neomycin were measured in the meat of cows slaughtered 2 hours and 7 hours after injection. Treatment with streptomycin i.v. resulted in significantly lower renal cortex drug levels than after the i.v. administration of other drugs. Injection of neomycin in a formulation containing benzylpenicillin procaine resulted in higher neomycin concentrations in the renal cortex compared to the levels of the drug found after i.v. injection of the drug. Results are discussed the possible role played by drug interaction on the persistence of aminoglycoside antibiotics in the kidneys after treatment with different dosage forms of these drugs.