Gentamicin sulfate in the horse: serum, synovial, peritoneal, and urine concentrations after single dose intramuscular administration

Ten healthy adult mares were given a single intramuscular dose (2.2 mg/kg) of gentamicin sulfate. Over a 48-h period, gentamicin concentrations were measured serially in the serum of all ten mares and in synovial fluid, peritoneal fluid, and urine of six of the mares. The mean peak serum gentamicin concentration was 5.73 micrograms/ml at 1 h. Gentamicin was detected in synovial fluid and peritoneal fluid, with mean peak gentamicin concentrations of 2.41 micrograms/ml and 3.92 micrograms/ml, respectively, observed at 2 h. These concentrations declined in parallel with serum concentrations and were not measurable at 48 h. Urine gentamicin concentration was relatively high, with a mean peak concentration of 424.9 micrograms/ml at 1 h after drug administration.