Effect of furosemide on the pharmacokinetics of gentamicin in patients.

The clearances of inulin and gentamicin were studied before and after intravenous furosemide in seven patients. There was a significant fall in glomerular filtration rate after furosemide and a similar though less marked fall in gentamicin clearance in six of the seven subjects. Small but consistent increases in plasma gentamicin concentrations were observed after furosemide. The reduction in clearance may explain the enhanced risk of nephrotoxicity in patients receiving both aminoglycosides and diuretics.