Local penetration of gentamicin into the femoral cortex of rats.

To investigate the extent of local penetration of antibiotic into the bone, a single dose of 10 mg/kg gentamicin sulphate was injected over the midshaft of the left femur in 12 young and 14 old rats. In some of the rats the injected gentamicin was dissolved in saline while in the others it was dissolved in dimethylsulphoxide (DMSO). Up to 120 minutes after the injection gentamicin concentrations were measured by the fluoroimmunoassay method in the serum, cortex and spongiosa of both femurs. In young rats gentamicin was shown to have penetrated directly into the bone and its presence was limited to the femoral cortex. In the old rats, on the other hand hematogenic was found to be the antibiotic spread in the femurs. No significant difference was observed between DMSO and saline as solvents in facilitating gentamicin penetration into the bone or capillaries in either age group.