The effect of a fat- and liquid-calcium-rich meal on the pharmacokinetics of single and multiple doses of fleroxacin in 20 healthy men and women was investigated in a randomized crossover fashion. Fleroxacin was administered as 400 mg daily for 3 days and as a single 400 mg dose. Concurrent administration of fleroxacin with food resulted in a statistically significant (P < or = 0.05) decrease in the area under the curve (13.9% for multiple-dose administration, 10% for single-dose administration) and in the peak concentration (25.9% for multiple-dose administration, 27% for single-dose administration) and a lengthening of the time to peak (more than doubled for single- and multiple-dose phases). In addition, by using an equivalence criteria of 80 to 125%, the two one-sided tests procedure indicated that the mean areas under the curves for fleroxacin administered in a fed and a fasted state were statistically bioequivalent (P < or = 0.05) for both the single- and multiple-dose regimens. Although a meal high in fat and containing liquid calcium reduces the peak concentration by approximately 25%, a minimal effect on bioavailability is seen with concomitant food administration. In addition, multiple-dose bioavailability studies appear to give similar information to single-dose studies while representing the clinical setting more closely.