Sparfloxacin is a broad-spectrum oral fluoroquinolone antimicrobial agent with a long elimination half-life (t(1/2)). Concurrent treatment with antacids has demonstrated a reduction in the oral absorption of many quinolones. This study was undertaken to determine an optimal time for dosing antacids in relation to sparfloxacin administration to minimize antacid-induced reduction in sparfloxacin bioavailability. This open-label, single-dose, randomized, four-way crossover study was conducted in 20 healthy male volunteers between the ages of 18 and 38 years. Treatments consisted of single 400-mg oral doses of sparfloxacin alone and with Maalox 30 mL given 2 hours before, 2 hours after, and 4 hours after oral administration of sparfloxacin. All 20 subjects completed the study. A 400-mg single oral dose of sparfloxacin was well tolerated both given alone and with Maalox. Maalox given 4 hours after sparfloxacin administration was the only regimen that did not cause a statistically significant reduction in the rate and extent of sparfloxacin absorption. The 90% confidence intervals comparing sparfloxacin alone with the preceding regimen in terms of area under the concentration-time curve from zero to infinity (AUC(0-infinity)) and maximum plasma concentration (Cmax) were within the range 80% to 125%. Administration of Maalox 2 hours before, 2 hours after, and 4 hours after sparfloxacin caused mean decreases in AUC(0-infinity) of 23%, 17%, and 5%, respectively. Corresponding decreases in mean Cmax values were 29% with Maalox administered 2 hours before sparfloxacin and 13% with Maalox administered 2 hours after sparfloxacin. The mean Cmax value was un affected when Maalox was administered 4 hours after sparfloxacin administration. The 90% confidence intervals for these comparisons with sparfloxacin alone were outside the 80% to 125% range and did not include 100%. Time to Cmax and t(1/2) were similar for all four regimens. The elimination rate of sparfloxacin was unaffected by concomitant administration with Maalox in healthy male volunteers.