Prevention of pyelonephritis due to Escherichia coli in rats with gentamicin stored in kidney tissue.

Although gentamicin is known to accumulate and persist in the kidneys after systemic administration, its antibacterial activity at this site has not been determined. In the present study the accumulation of gentamicin in rat kidneys before infection prevented obstructive pyelonephritis due to Escherichia coli despite heavy urinary tract infection on the obstructed pelvis; thus the kidneys were protected against infection in the absence of effective levels of gentamicin in the urine. Stored gentamicin also protected pyelonephritic rats from relapse after complete obstruction of the kidneys. The level of antimicrobial activity of gentamicin in whole kidney tissue was 95% less than that anticipated on the basis of levels measured after dilution of kidney tissue homogenates; this low level of activity apparently was due in part to high concentrations of solutes. In view of these results in rats, the possibility must be considered that despite reduced activity, gentamicin storage might be useful in the prophylaxis of kidney infection in patients with abnormalities of the urinary tract. In the treatment of established kidney infection, the dose of gentamicin could be reduced and the interval of its administration increased for minimal toxicity.