Antacids neutralize excess stomach acidity to relieve heartburn, sour stomach, acid indigestion, and stomach upset. They are also used to relieve the pain of stomach and duodenal ulcers. The acid-neutralizing capacity (ANC) of an antacid is the amount of acid that can be neutralized. Commercial antacids containing one or more bases are available to treat this condition by neutralizing the excess acid in the stomach. Antacids are available with various formulations as over the counter drugs (OTC). USP<301> describes a back titration method to a set endpoint of pH 3.5 to determine the acid-neutralizing capacity. This Application Note shows the determination of the acid-neutralizing capacity for alumina magnesia, simethicone chewable tablet, magaldrate and simethicone oral suspension.