The solution procured from the various parts of plants, by boiling them in water, is called a decoction. Decoctions are generally prepared from those articles which do not readily yield their active constituents to water, at a temperature below 100° C. (212° F.). Yet it must be remembered, that as most plants contain starch, gum, and other inert matters, which are readily soluble in boiling water, these will generally be found associated with the remedial principles in a decoction. Medicines containing volatile principles, or substances liable to be changed into insoluble and inert matters at a boiling heat, should never be subjected to decoction. When, however, decoction is determined upon, the drugs should be sliced, bruised, or powdered, according to their character, and placed in an earthenware, glass, or iron vessel of suitable size, the latter being lined internally with enamel. In most instances, tin vessels may be employed, but copper, brass, iron, or zinc vessels, on account of their liability to oxidation, or incompatibility with such principles as tannic acid, are apt to prove injurious, and should not, therefore, be used. The water employed should be pure and clear, and the boiling should not be continued for too long a period. The vessel should be kept covered. The decoction should be strained before it cools.
In decoctions where several drugs are employed, each should be placed in the boiling water at periods adapted to the time required to obtain its soluble constituents. Some plants require to be boiled for some minutes, while others yield all their virtues if added toward the termination of the process. Volatile agents should be added after the decoction, which should be kept closely covered until cold, has been removed from the fire.
Decoctions are now seldom ordered from the pharmacist, but are made a matter of domestic management; hence, with but few exceptions, a list of decoctions is omitted herein, an explanation of the general rules relating to them being deemed sufficient. Physicians usually prepare decoctions by allowing 1 ounce of the drug to 1 pint of water, the dose depending on the activity of the agent, or the physiological effect required.
Decoctions are liable to speedy change or decomposition; consequently they should be made in small quantities. Decoctions have been largely superseded by the more stable and elegant pharmaceutical preparations of the present. Owing to the fact, however, that many are occasionally employed, we give formulae for those most important. The U. S. P. gives the following general method for the preparation of decoctions:
"An ordinary decoction, the strength of which is not directed by the physician nor specified by the Pharmacopoeia, shall be prepared by the following formula: Take of the substance, coarsely comminuted, fifty grammes (50 Gm.) [1 oz. av., 334 grs.]; water, a sufficient quantity to make one thousand cubic centimeters (1000 Cc.) [33 fl℥, 391♏]. Put the substance into a suitable vessel provided with a cover, pour upon it one thousand cubic centimeters (1000 Cc.) [33 fl℥, 391♏] of cold water, cover it well and boil for 15 minutes. Then let it cool to about 40° C. (104° F.), express, strain the expressed liquid, and pass enough cold water through the strainer to make the product measure one thousand cubic centimeters (1000 Cc.) [33 fl℥, 391♏]. CAUTION.—The strength of decoctions of energetic or powerful substances should be specially prescribed by the physician"—(U. S. P.).
The Pharmacopoeia, of 1880, directed decoctions of 10 per cent drug strength. Those of the present U. S. P. have a strength of 5 per cent, and only two are recognized.
Decoctions Formerly Official.—The following decoctions were official in the U. S. P. of 1870: DECOCTUM CHIMAPHILAE, Decoction of Pipsissewa; DECOCTUM CINCHONAE FLAVAE, Decoction of Yellow Cinchona; DECOCTUM CINCHONAE RUBRAE, Decoction of Red Cinchona; DECOCTUM CORNUS FLORIDAE, Decoction of Dogwood; DECOCTUM DULCAMARAE, Decoction of Bittersweet; DECOCTUM HAEMATOXYLAE, Decoction of Logwood; DECOCTUM HORDEI, Decoction of Barley; DECOCTUM QUERCUS ALBAE, Decoction of White Oak Bark; DECOCTUM SENEGAE, Decoction of Seneka; DECOCTUM UVAE URSI, Decoction of Uva Ursi.
All were prepared (excepting decoction of barley) by boiling for 15 minutes a troy ounce of the drug in a pint of water, straining and finally bringing the finished product to 1 pint by adding to it a sufficient quantity of water.