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The pharmacokinetics of gatifloxacin (400 mg orally) and the influence of the antacid aluminum magnesium hydroxide (20 ml of Maalox 70) on the bioavailability of gatifloxacin in 24 healthy volunteers were assessed. In an open, randomized, six-period crossover study, the volunteers received either gatifloxacin alone (treatments A and D); aluminum magnesium hydroxide concomitant with gatifloxacin (treatment C); or aluminum magnesium hydroxide 2 h before (treatment B), 2 h after (treatment E), or 4 h after gatifloxacin administration (treatment F). Gatifloxacin concentrations were measured by a validated bioassay and high-performance liquid chromatography. Pharmacokinetics of a single 400-mg dose of gatifloxacin alone were characterized as follows (mean +/- standard deviation): peak concentration (Cmax), 3.8 +/- 0. 5 (treatment A) and 3.4 +/- 0.9 (treatment D) microgram/ml; time to Cmax, 1.4 +/- 0.8 (treatment A) and 1.7 +/- 0.7 (treatment D) h; area under the curve from time zero to infinity (AUC0-infinity), 33. 5 +/- 5.9 (treatment A) and 31.4 +/- 3.4 (treatment D) microgram. h/ml; urine recovery, (83 +/- 6)% (treatment A) and (84 +/- 8)% (treatment D). Comparison of the results obtained by bioassay showed a good correlation. Aluminum magnesium hydroxide administration 2 h before (treatment B) or concomitant with (treatment C) gatifloxacin decreased the Cmax by 45% (2.1 +/- 1.2 microgram/ml) or even 68% (1.2 +/- 0.4 microgram/ml) highly significantly (P < 0.01). AUC0-infinity was significantly reduced from 33.5 +/- 5.9 to 19.4 +/- 6.9 microgram. h/ml (by 42%) or even to 11.9 +/- 3.3 microgram. h/ml (by 64%) (P < 0. 01). If aluminum magnesium hydroxide was given 2 h after gatifloxacin (treatment E), there was no significant reduction of concentration in serum but AUC0-infinity was significantly reduced from 31.4 +/- 3.4 to 25.9 +/- 5.3 microgram. h/ml (18%) (P < 0.01). Aluminum magnesium hydroxide given 4 h after gatifloxacin (treatment F) showed no influence on the gatifloxacin pharmacokinetics. Therefore, the optimal time between gatifloxacin application and the intake of an aluminum-containing antacid should be 4 h.

In an open, randomized, triple crossover study, the effects of cisapride and sucralfate on the pharmacokinetics of sparfloxacin were assessed. Fifteen healthy volunteers received 400 mg of sparfloxacin as a single oral dose on day 0. In a random order, concomitant doses of 10 mg of cisapride three times daily from day -2 to day 2 and 1 g of sucralfate four times daily from day -2 to day 0 were administered. Sparfloxacin concentrations were measured by bioassay and high-performance liquid chromatography. Pharmacokinetic parameters for sparfloxacin alone were as follows (mean +/- standard deviation): maximum concentration of drug in serum (C(max)), 1.27 +/- 0.39 microg/ml; time to C(max) (T(max)), 4.1 +/- 1.9 h; area under the concentration-time curve (AUC), 35.0 +/- 9.7 microg x h/ml; mean residence time, 28.5 +/- 5.7 h; half-life (t1/2), 20 +/- 4 h; urinary recovery (UR x f), 11.0% +/- 2.7%; and metabolite-sparfloxacin ratio in urine, 2.6. For the cisapride group there was a significant decrease in the sparfloxacin T(max) (1.9 +/- 2.1 h) and a significant increase in C(max) (1.74 +/- 0.73 microg/ml). The QTc interval for patients receiving sparfloxacin and cisapride was prolonged by 7.7% compared to the QTc interval during medication-free periods. Significant differences in the values for the group receiving sucralfate compared to the values for the group receiving sparfloxacin alone were found: C(max), 0.77 +/- 0.31 microg/ml; AUC, 18.6 +/- 5.8 microg x h/ml; t1/2, 26 +/- 10 h; and UR x f, 5.8 +/- 1.8%. Concomitant adminstration of cisapride accelerates the absorption and increases the peak concentration of sparfloxacin without having a significant effect on the extent of bioavailability. Coadministration of sucralfate leads to a 44% decrease in the bioavailability of sparfloxacin.