Comparative clinical pharmacology of gentamicin and tobramycin in neonatal calves

Abstract

The minimum inhibitory concentrations (MIC) of gentamicin, and a closely related aminoglycoside--tobramycin, for gram-negative bacteria isolated from cattle (326 strains of E. coli, 240 Salmonella sp., 17 Klebsiella, 6 Aerobacter aerogenes, 32 Pseudomonas aeruginosa) was 0.25 mu g/ml for at least 75% of the strains tested and 2.0 mu g/ml for more than 95% of the isolates. Intramuscular injection of gentamicin at 1.5 mg/kg/day and 3.0 mg/kg/day for three days did not alter normal renal function. Neither antibiotic was bound to serum proteins. When administered at 1.5 mg/kg, both antibiotics produced serum levels in excess of the MIC during 10 hours and after the 3.0 mg/kg dose was injected effective blood levels were maintained during 12 hours. Gentamicin blood levels were rather erratic and unpredictable in the majority of animals treated. This behaviour was not observed with tobramycin.