Influence of antacid administrations on aspirin absorption in patients with chronic renal failure on maintenance hemodialysis.

In order to investigate the possible interaction between oral aspirin and antacids in uremic patients on chronic hemodialysis, we administered to 5 uremic patients: (1) aspirin alone; (2) aluminum-magnesium hydroxide with aspirin; (3) aluminum-magnesium hydroxide followed (two hours) by aspirin; (4) calcium carbonate simultaneously with aspirin; and (5) calcium carbonate followed (two hours) by aspirin. In all the occasions, aspirin was given two hours after a standard lunch. Both antacid preparations induced comparable changes in aspirin mean peak plasma concentration (Cmax), if given simultaneously with aspirin, whereas no difference was found in other pharmacokinetic parameters. When antacids were followed (two hours) by aspirin, both Cmax and time of maximum concentration (Tmax) were significantly altered in respect to the value with aspirin alone. No changes in the time course of post aspirin serum thromboxane B2 were detected when aspirin and antacids were administered simultaneously, but the inhibition of serum thromboxane B2 was delayed when antacids were followed (two hours) by aspirin. These results indicate that the administration of antacids to uremic patients interferes with absorption of oral aspirin. This interference can be minimized if aspirin and antacids are given simultaneously.