Effect of antacids on the plasma concentration of phenoperidine

The effect of antacids on the plasma concentration of phenoperidine was studied in six volunteers. All subjects received the same dose of phenoperidine (15 micrograms kg-1) on different occasions in the presence, and absence of, an antacid preparation. In control studies, secondary peaks in the plasma concentration of phenoperidine were invariably observed; these were entirely eliminated, or modified substantially, by the concurrent administration of antacids. In the latter conditions, plasma concentrations of phenoperidine were greater during the first 20 min, and the area under the plasma concentration--time curve between 0 and 20 min was significantly greater than in control studies. In contrast, the plasma clearance of the drug was almost identical in control conditions and during treatment with antacids. After the oral administration of phenoperidine to two subjects, the systemic bioavailability of the drug was 9.9% and 13.9% respectively.