Chronic dose urinary and serum pharmacokinetics of norfloxacin in the elderly.

1. Norfloxacin was administered as two daily 400 mg oral doses to eight elderly patients requiring treatment for urinary tract infections. Blood specimens were obtained for pharmacokinetic profiles following the first and fifteenth doses. Further specimens were obtained before each morning's dose of norfloxacin. Specimens of urine were obtained to ascertain if adequate antimicrobial concentrations were reached in these patients with diminished renal function. 2. Norfloxacin half-life was consistent with that expected in mild renal impairment and was not different between the first and fifteenth doses. Based on ratios of AUC values, accumulation is probably related to renal function, being greatest for creatinine clearance values below 30 ml min-1. 3. On the great majority of occasions, the urinary concentrations of norfloxacin exceeded 20 micrograms ml-1. On days 2-7, the mean percentage 12 h renal elimination of norfloxacin was 18.6 +/- 1.47 (mean of 82 separate observations). Norfloxacin 400 mg twice daily was well tolerated in this group of elderly patients and produced adequate antimicrobial concentrations in urine.