Acidum Lacticum, B.P. Lactic Acid.

C₃H₆O₃ = 90.048.

Lactic acid, CH₃CHOHCOOH, is prepared usually by the fermentation of lactose, with subsequent purification. The official preparation is an aqueous solution, containing 75 per cent. of real acid. An acid of this strength is also official in the U.S.P. It occurs as a colourless, syrupy, odourless, and somewhat hygroscopic liquid. Specific gravity, 1.21 (about 1.206 at 25°). More accurate results than are yielded by the official titration process for determining the percentage of the lactic radicle which it contains, may be obtained by adding excess of alkali, boiling, and titrating back with acid, as the anhydride or lactone is sometimes present in appreciable amount.

Miscible freely with water, alcohol, or ether; almost insoluble in chloroform.

Action and Uses.—Lactic acid is employed as a caustic to destroy tuberculous ulcerations of the pharynx and larynx. It has also been employed as a local application to lupus and (1 in 15) to diphtheritic membranes. A 1 in 3 dilution has been recommended as an application in alopecia. It is administered in mixtures in the form of the diluted acid, often with iron and calcium lactates, in the treatment of atonic dyspepsia, and vesical catarrh. Sometimes it produces pains in the joints, and it was believed at one time to be the cause of rheumatism. Lactic acid is an intermediate product in the oxidation of carbon compounds in the body; normally it is burned to CO₂, but in many conditions of poisoning, especially phosphorus and arsenic, this oxidation fails, and an acidaemia results. Diabetic coma is also largely due to an acidaemia of this nature. Recently, nascent lactic acid has been much employed as an intestinal antiseptic. For this purpose living lactic acid bacilli are ingested with suitable material for their growth and multiplication. (See Lac Coactum.)

Dose.—1 to 3 mils (15 to 45 minims).

PREPARATIONS.

Acidum Lacticum Dilutum, B.P., 1885.—DILUTED LACTIC ACID.

Lactic acid, 15; distilled water, to 100. Taken internally has a similar effect to the other diluted acids. Dose.—2 to 8 mils (1/4 to 2 fluid drachms).

Syrupus Acidi Lactici, B.P.C.—SYRUP OF LACTIC ACID. 1 in 40.

Dose.—4 to 8 mils (1 to 2 fluid drachms).

The British Pharmaceutical Codex, 1911, was published by direction of the Council of the Pharmaceutical Society of Great Britain.