A number of fluoroquinolones have been shown to interact adversely with theophylline. We studied the influence of coadministration of temafloxacin, a new fluoroquinolone antimicrobial agent, on steady-state theophylline pharmacokinetics. Twelve healthy subjects (8 males, 4 females; average age and weight 34 years and 62 kg, respectively) were given oral controlled-release theophylline in an individualized dosage to achieve a target plasma level of 10 mg/L. Once steady state was achieved, temafloxacin 600 mg given orally twice daily was concomitantly administered for 4-5 days. Serial blood samples were collected before and during simultaneous temafloxacin administration and plasma assayed for theophylline using a high-performance liquid chromatography technique. Theophylline pharmacokinetic parameters were determined noncompartmentally, and results of single and combined administration were compared. Theophylline plasma concentrations did not differ significantly with temafloxacin coadministration, and similar area-under-the-curve (AUC) values were observed. Theophylline oral clearance increased from 2.67 +/- 1.01 L/hour to 2.69 +/- 0.93 L/hour, when given alone and with temafloxacin, respectively (p = 0.92). Only 2 of 12 subjects showed an appreciable decrease in clearance when theophylline and temafloxacin were administered together, while 2 subjects demonstrated increases greater than 15% and 8 showed no change. We conclude that temafloxacin does not interact significantly with theophylline and that these agents can be safely administered together.