Evaluation of antacid suspensions containing aluminum hydroxide and magnesium hydroxide.

Liquid antacid suspensions containing aluminum hydroxide and magnesium hydroxide were evaluated for composition, antacid properties, and product quality. The equivalent aluminum oxide and magnesium hydroxide content was determined by chelatometric titration, and sodium content was determined by flame photometry. Antacid properties measured were acid-consuming capacity, antacid effectiveness (preliminary antacid test, acid-neutralizing capacity test), and pH-stat titration. Content uniformity, consistency of the antacid properties, and microbiological content were examined for each product. Data are presented for 36 products for which samples from four or more lots were obtained. The ratio of percentage of equivalent aluminum oxide to percentage of magnesium hydroxide ranged from 1:0.6 to 1:3.5; this range allows for selection of the desired balance between the laxative effect of magnesium hydroxide and the constipating effect of aluminum hydroxide. Based on a daily dose of 280 meq of antacid, the sodium content of the products tested ranged from less than 2% to approximately 45% of the 500 mg per day of sodium allowed in a sodium-restricted diet. The concept of bioavailability was related to the amount of the antacid reacting at pH 3, 37 degrees C during the estimated gastric residence time of 15 minutes. Antacid suspensions are available which will react almost completely (neutralizing greater than 90% of the theoretical quantity of acid) during the estimated gastric residence time. Approximately 4% of the samples contained unacceptable numbers of bacteria. An antacid suspension cannot be adequately evaluated by a single test; choice of a product should be based on an evaluation that integrates several characteristics including sodium content, time and volume required to neutralize a given amount of acid, and uniformity of content.