The pharmacokinetics of rufloxacin, after repeated doses, was evaluated in 12 elderly patients with lower respiratory tract infections. Patients were given a single loading dose of 400 mg on the first day of treatment and single daily maintenance doses of 200 mg for the next 6-9 days. Serum concentrations of the drug were determined by high-performance liquid chromatography (HPLC) at regular intervals during treatment and fitted to a one-compartment open model for repeated doses. The maximum serum concentration after the first dose was 6.46 +/- 1.06 (mean +/- SEM) micrograms/ml and was reached in 4.3 +/- 0.8 h after the first administration. The elimination half-life was 28.7 +/- 4.1 h. The area under the serum levels-time curve from 0 to 24 h was 103 +/- 14 micrograms/h/ml after the first dose. On the last day of observation it increased to 155 +/- 28 micrograms/h/ml, with a mean extent of accumulation of 2.3 +/- 0.3 times. The elimination half-life was comparable to those in other studies in healthy young subjects, while plasma levels were about 80% higher. These results suggest that in elderly patients elevated drug concentrations may be reached in the serum. Although no untoward reactions related either to the drug concentration in serum or the dose have been noted with rufloxacin, this patient population should nevertheless be monitored carefully for adverse effects.