Comparative Effects of Liquid Antacids on Esophageal and Gastric pH in Patients with Heartburn

This double-blind crossover trial compared the postmeal effects of single doses of liquid antacids on esophageal and gastric pH in patients with a history of heartburn. Treatment consisted of one of two antacids containing the same active components---aluminum and magnesium hydroxide---but different in vitro acid-neutralizing capacities (ANCs). The pH was assessed continually from 1 h before a refluxogenic meal to 4 h after its completion in 24 subjects who received 20 ml of Mylanta((R)) Double Strength (MYL-20: ANC = 101.6 mEq), 20 or 30 ml of Extra-Strength Maalox((R)) Plus (MA-20, MA-30: ANC = 116.2 and 174.3 mEq, respectively), or placebo (ANC = 0) in random order. Esophageal pH increased rapidly and significantly (p < 0.05) to peak values of 7.0--7.4 with antacid. The increase in mean esophageal pH values was significantly higher (p < 0.05) than placebo for 30 min with MA-20 and for at least 70 min with MYL-20 and MA-30. In contrast, gastric pH rose slowly to mean peaks of 2.9--3.1 with antacid. During this interval, only MYL-20 was associated with significant improvements (p < 0.05 versus placebo) in total number of reflux episodes and total time that esophageal pH measured >4. Thus, ANC alone is not a useful guide in predicting in vivo antacid behavior, as in this study where the antacid dose with the lowest ANC demonstrated a duration of action as long or longer than that of antacid doses with higher ANC values. The rapid, prolonged increases in esophageal pH that preceded modest changes in gastric pH strongly suggest that the lower esophagus is the primary site of antacid action for heartburn relief.