Antacids are remedies employed to lessen or counteract acidity. The excessive acidity for which antacids are given may be present in the stomach, intestines, or urine.

Antacids are divided into direct and indirect or remote. Direct antacids lessen the acidity in the stomach, to which they are directly applied. Remote antacids lessen the acidity of the urine. Some substances have both actions, such as potash and soda, or the carbonates and bi-carbonates. Other substances, such as the citrates, tartrates, and acetates of these bases, have no power to lessen acidity in the stomach, but, after absorption into the blood, they appear to undergo combustion, and become converted into carbonates. In this form they are excreted in the urine, and lessen its acidity.

1 Beaumont, Physiology of Digestion, Burlington, 1847, p. 118.

Ammonia and its carbonate are direct antacids, but not remote antacids. They lessen acidity in the stomach or intestines, but after absorption they undergo change, and are eliminated in the form of urea, and, according to some, of nitric acid, so that they do not lessen the acidity of the urine.

Direct Antacids. - Liquor potasssae, potassium carbonate, potassium bi-carbonate, liquor sodae, sodium carbonate, sodium bicarbonate, liquor Utilise, lithium carbonate, lithium bi-carbonate, magnesia, magnesium carbonate, magnesium bi-carbonate, lime-water, saccharine solution of lime, chalk.

Direct but not Remote Antacids. - Ammonium carbonate, aromatic spirit of ammonia.

Remote Antacids. - Potassium acetate, potassium citrate, potassium tartrate, potassium bi-tartrate, sodium acetate, sodium citrate, tartarated soda, lithium citrate.