Sodium carbonate is used as an alkalizing agent in injectable, ophthalmic, oral, and rectal formulations. In effervescent tablets or granules, sodium carbonate is used in combination with an acid, typically citric acid or tartaric acid. When the tablets or granules come into contact with water, an acid– base reaction occurs in which carbon dioxide gas is produced and the product disintegrates. Raw materials with low moisture contents are required to prevent the early triggering of the effervescent reaction. As an alkalizing agent, concentrations of sodium carbonate between 2% and 5% w/w are used in compressed tablet formulations. As an effervescent agent, concentrations of sodium carbonate up to 10% w/w can be used. Therapeutically, sodium carbonate is also used as an oral antacid.