Effect of antacids on activity of oral hypoglycemics

The effect of some antacids on the dissolution and hypoglycemic activity of acetohexamide, tolazamide, and tolbutamide tablets was investigated, as was the adsorption of the three drugs onto the antacids. The dissolution rates of the three drugs in the presence of magnesium oxide, aluminum hydroxide, magnesium carbonate, and calcium carbonate increased (0.5-1 hr) and then plateaued or decreased (1-3 hr). Magnesium trisilicate directly suppressed the dissolution of the three drugs. The antacids reduced the hypoglycemic activity of tolbutamide in the following order:magnesium trisilicate greater than magnesium oxide greater than aluminum hydroxide greater than magnesium carbonate greater than calcium carbonate. The same order occurred for the first three antacids with acetohexamide and tolazamide. Decreased hypoglycemic activity of the drugs may have been due to their adsorption to the coadministered antacids.