The mechanical response of alginate rafts formed by mixing liquid alginate antacid medication (Gaviscon Extra Strength Liquid Antacid) with acidic solutions was investigated by deforming isolated rafts in a shear rheometer. As rafts were deformed to varying magnitudes of applied strain, rheological parameters were identified and related to the overall strength, durability, and recoverability of rafts formed at different pH (1.1-1.7) and aging conditions (0.5-4 h). Rafts formed in the lowest acidity solutions (pH 1.4, 1.7) were elastically weak (G'₀ = 60 , 42 Pa for un-aged raft) yet maintained their elasticity during applied shear deformation to large values of strain (γc∼90%, 50%, where G'≈G″), and displayed a low-to-moderate level of elastic recovery following large-strain deformation. Rafts formed in the highest acidity solution had the greatest strength (G'₀ = 500 Pa for un-aged raft and 21.5 kPa for rafts after 0.5 h of aging), reduced durability (γc∼2.5%, independent of aging), and displayed the greatest recoverability. A trade-off existed between un-aged raft strength and durability while recovery was dependent on durability, solution pH, and age. Rheometry-based evaluations of alginate rafts could be used for the informed design of future gastric retention and antacid products.

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.