Norfloxacin versus co-trimoxazole for treatment of urinary tract infections in adults: microbiological results of a coordinated multicentre study.

In a prospective, coordinated, double-blind multicentre trial, outpatients with urinary tract infections were randomized to 7 days b.i.d. treatment with norfloxacin 200 mg or 400 mg or trimethoprim/sulfamethoxazole. The most prevalent species was Escherichia coli (76.6%) followed by Staphylococcus saprophyticus (14.1%), the latter of which showed a marked seasonal variation with peak incidence during late summer. Minimum inhibitory concentrations (MICs) of 11 antibiotics for 651 pre-treatment bacterial strains were studied. Norfloxacin was found to be active against all isolates with MICs less than or equal to mg/l for gram-negative and less than or equal to 8 mg/l for gram-positive isolates. Reduced susceptibility to norfloxacin was seen in 2 strains of E. coli and 1 of Klebsiella pneumoniae from patients with persisting or relapsing infections following treatment with norfloxacin 400 mg b.i.d. Of other antibiotics tested, ampicillin, cephalothin and sulfamethoxazole were found to have poor activity against many gram-negative isolates while nalidixic acid and mecillinam lacked activity against all gram-positives. Cefotaxime, gentamicin, trimethoprim and trimethoprim/sulfamethoxazole were generally highly active against the isolated bacterial strains.