Antacid effects on the gastrointestinal absorption of riboflavin

The effect of aluminum hydroxide, magnesium hydroxide, and a combination of aluminum-magnesium hydroxide suspensions on the oral absorption of riboflavin was examined in five subjects. Coadministration of aluminum hydroxide or magnesium hydroxide suspension with riboflavin (30 mg) resulted in an increase in time of peak urinary excretion rate of riboflavin when compared with control studies. There was no increase in the peak excretion rate or total urinary excretion of riboflavin when the antacid-treated subjects were compared to the control studies. In vitro experiments indicated that significant binding of riboflavin to the aluminum hydroxide and magnesium hydroxide suspensions occurred. The results of the present investigation are consistent with the reported effect of aluminum ion on GI motility and the known influence of gastric emptying on the absorption of riboflavin from the GI tract.