The effect of antacids on the absorption of riboflavin from the gastrointestinal tract



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The effect of various over-the-counter antacids on the rate of gastric emptying was evaluated in both in vivo and in vitro studies using riboflavin as a test drug. In vivo studies, using five male volunteers, showed that only aluminum hydroxide gel had any significant effect (p<0.05) on two of three categories observed (time of peak riboflavin excretion and peak rate of riboflavin excretion). No differences in bioavailability of riboflavin were noted with co-administration of the antacids. The percent of riboflavin binding to antacid as a function of both riboflavin concentration and antacid amount was determined in the in vitro studies along with the effect of antacid and hydrochloric acid concentration on the pH of riboflavin-antacid suspensions. Magnesium hydroxide exhibited the highest percent binding and pH readings. The smooth muscle relaxant properties of aluminum hydroxide may account for the significant level of delayed gastric emptying noted with this antacid. Although magnesium hydroxide showed no significant difference in riboflavin absorption compared with control values, higher values were observed in 4 out of the 5 subjects for time of peak riboflavin excretion, peak rate of riboflavin excretion, and bioavailability of riboflavin. This suggests that additional studies are needed to evaluate the potential of magnesium hydroxide to alter gastric emptying and drug absorption.