ATC Group: A02A Antacids

Anatomical Therapeutic Chemical Classification System



Hierarchical Position


Active Ingredients

Chemical substance

Aluminium hydroxide is a slow-acting antacid. It is used to provide symptomatic relief in gastric hyperacidity. In addition, the antipeptic and demulcent activity of aluminium hydroxide helps to protect inflamed gastric mucosa against further irritation by gastric secretions.

Calcium carbonate releases, in a pH-dependent manner, calcium ions in the stomach. Calcium carbonate is widely used as antacid and extensively used as a dietary supplement.

Hydrotalcite is a layered double hydroxide of general formula Mg6Al2CO3(OH)16·4(H2O), whose name is derived from its resemblance with talc and its high water content. The carbonate anions that lie between the structural layers are weakly bound, so hydrotalcite has anion exchange capabilities. Hydrotalcite is also used as an antacid.

Magaldrate is a common antacid drug that is used for the treatment of duodenal and gastric ulcers, esophagitis from gastroesophageal reflux.

Magnesium carbonate, MgCO3 (archaic name magnesia alba), is an inorganic salt. The most common magnesium carbonate forms are the anhydrous salt called magnesite (MgCO3) and the di, tri, and pentahydrates known as barringtonite (MgCO3·2 H2O), nesquehonite (MgCO3·3 H2O), and lansfordite (MgCO3·5 H2O), respectively. The primary use of magnesium carbonate is the production of magnesium oxide by calcining.

Magnesium hydroxide is practically insoluble in water and solution is not effected until the hydroxide reacts with hydrochloric acid in the stomach to form magnesium chloride. Its neutralising action is almost equal to that of sodium bicarbonate. When the dose is in excess of that required to neutralise the acid the intragastric pH may reach pH 8 or 9. Acid rebound following magnesium hydroxide is clinically insignificant. Magnesium hydroxide has an indirect cathartic effect resulting from water retention in the intestinal lumen.

Magnesium oxide (MgO), or magnesia, is an empirical formula of MgO and consists of a lattice of Mg2+ ions and O2− ions held together by ionic bonding.