Fate of oral neutralizing antacid and its effect on postprandial gastric secretion and emptying.

The fate and neutralizing efficiency of oral antacids (aluminum and magnesium hydroxides) as well as their effect on postprandial gastric function were quantified in 6 patients with duodenal ulcer disease. We employed a double-marker technique for measurement of gastric secretion and emptying and combined this with back-titration of the gastric samples and analysis of aluminum to trace the fate of antacid in the stomach and duodenum. These studies show that: (a) antacid therapy with aluminum and magnesium hydroxides significantly increases gastric secretion; (b) intragastric neutralization of gastric acid produces a significant and substantial decrease in net acid output (acid secreted minus acid neutralized), but the beneficial effects of neutralization are partially offset by incomplete intragastric formation of aluminum trichloride; (c) most but not all of the ingested antacid is utilized in acid neutralization in the stomach (average 78.6% in our 6 patients); and (d) antacid therapy does not modify the absolute rate of postprandial gastric emptying, but increases dilution of gastric contents, expanding the intragastric volume. Thus, the fractional gastric emptying rate declines, and this, in turn, should enhance antacid utilization by delaying its emptying.