Abstract
The oral absorption of dexamethasone in humans was compared to its absorption when coadministered with magnesium trisilicate. The bioavailability of dexamethasone was estimated by measuring the suppressive effect of the drug on the daily excretion of endogenous steroids. Administration of 1mg of dexamethasone to six healthy male volunteers significantly decreased the urinary excretion of 11-hydroxycorticosteroids. However, the coadministration of magnesium trisilicate with dexamethasone decreased its absorption, as indicated by the increased urinary excretion of 11-hydroxycorticosteroids. The decrease in absorption was attributed to drug adsorption on the antacid surface. These results confirm previous in vitro findings.