[Netilmicin in refractory urinary tract infections. Good therapeutic effect in spite of long dosage intervals].

Aminoglycoside antibiotics are useful--despite potential toxicity--for treating urinary tract infection when other antibacterial agents have failed to eradicate bacteriuria. That this is true of the recently introduced aminoglycoside netilmicin was shown by 16 cases of tenacious and frequently recurring urinary tract infection. In contrast to previous recommendations, but relying on well known pharmacokinetic data which show prolonged urinary excretion of aminoglycosides, netilmicin was administered according to the following dosage schedule: Intramuscular injections of 3 mg/kg in cases where renal function was unimpaired, and of 2 mg/kg where it was reduced, were administered at dosage intervals of 1 to 4 days. Peak serum levels of netilmicin measured 1 hour after intramuscular injection were within the expected range of 8-14 micrograms/ml (3 mg/kg) and 6-10 micrograms/ml (2 mg/kg). As a result of the long dosage intervals the serum trough levels were usually far below 1 microgram/ml except in patients with moderate renal failure. Urinary concentrations of netilmicin, however, remained for the most part above the limit of antibacterial activity throughout the dosage intervals of 1 to 4 days. One week after the usual three weeks treatment course, urinary concentrations were still between 1 and 5 mcg/ml, and slowly decreasing amounts of the drug could be detected at least in traces up to 3 months beyond the last dose. Considering the type of urinary tract infections selected to receive netilmicin, the response to treatment was satisfactory and seemed unaffected by the long dosage intervals. Bacteriological cure was achieved in 5 of 11 infections associated with chronic pyelonephritis or analgesic nephropathy and in 4 of 5 urinary infections in patients with renal transplants. Treatment failures could be accounted for by obstructive lesions, stones, and in one transplanted patient by infection localized to her own shrunken kidneys. No instance of ototoxicity or nephrotoxicity due to netilmicin could be detected. Netilmicin administered according to the dosage schedule described can be recommended for ambulatory treatment of tenacious, recurring urinary tract infections due to gram-negative bacteria and refractory to cure by the usual oral antibiotic therapy.