Decocta. U. S. Decoctions.
Tisanes par deccetion, Decoctions, Fr.; Abkochungen, G.; Decotti, It.; Cocimiento, Sp.
Decoctions are solutions of vegetable principles, obtained by boiling the substances containing these principles in water. Vegetable tissues generally yield their soluble ingredients more readily, and in larger proportion, to water maintained at the point of ebullition, than to the same liquid at a lower temperature. Hence decoction is occasionally preferred to infusion as a mode of extracting the virtues of plants, when the call for the remedy is urgent, and the greatest possible activity in the preparation is desirable. The process should be conducted in a covered vessel, so as to confine the vapor over the surface of the liquid, and thus prevent the access of atmospheric air, which sometimes exerts an injurious agency upon the active principle. The boiling, moreover, should not, as a rule, be long continued, as the ingredients are apt to react on one another, and thus lose, to a greater or less extent, their original character. The substance submitted to decoction should if dry be either powdered or well bruised, if fresh should be sliced, so that it may present an extensive surface to the action of the solvent; and previous maceration for some time in water is occasionally useful by overcoming the cohesion of the vegetable fiber. Should the physician not happen to prescribe this preliminary comminution, the pharmacist should not omit it.
All vegetable substances are not proper objects for decoction. In many the active principle is volatile at a boiling heat, in others it undergoes some change unfavorable to its activity, and in a third set is associated with inefficient or nauseous principles, which, though insoluble or but slightly soluble in cold water, are abundantly extracted by that liquid at the boiling temperature, and thus encumber, if they do not positively injure, the preparation. In all these instances, infusion is preferable to decoction. Besides, by the latter process more matter is often dissolved than the water can retain, so that upon cooling a precipitation takes place and the liquid is rendered turbid, and this constitutes the greatest objection to this class of preparations. When the active principle is thus dissolved in excess, the decoction should always be strained while hot, so that the matter which separates on cooling may be mixed again with the fluid by agitation at the time of administering the remedy. In compound decoctions, the ingredients may be advantageously added at different periods of the process, according to the length of boiling requisite for extracting their virtues; and, should one of them owe its activity to a volatile principle, the proper plan is, at the close of the process, to pour upon it the boiling decoction, and allow the liquor to cool in a covered vessel.
As a rule, glass or earthenware vessels should be preferred, as those made of metal are sometimes corroded by the ingredients of the decoction, which thus become contaminated. Vessels of clean cast-iron or common tin, or of block tin, are preferable to those made of copper, brass, or zinc; but iron pots should not be used where astringent vegetable substances are concerned.
Decoctions, from the mutual reaction of their constituents, as well as from the influence of the air, are apt to spoil in a short time. Hence they should be prepared only when wanted for use, and should not be kept, when the "weather is warm, for a longer period than forty-eight hours.
The tendency of modern medicine and pharmacy has been decidedly against the employment of decoctions; their nauseous taste, bulky dose, repulsive appearance, and non-permanent character have been powerful reasons for causing their retirement, while the use of tinctures and fluidextracts has largely increased. In the 1880 revision of the U. S. Pharmacopoeia the number of official decoctions was reduced to two, and a general formula was appended for the guidance of the pharmacist. The U. S. P., 1890, reduced the strength of the general formula for decoctions from 10 per cent. to 5 per cent., and this strength was retained in the U. S. P. VIII and IX, as will be seen from the following: "Decoctions must be freshly made from the drugs, and, when the strength of decoctions is not otherwise directed, they are to be prepared by the following general formula:
"The Drug, coarsely comminuted, fifty grammes [or 1 ounce av., 334 grains]; Water, a sufficient quantity, to make one thousand mils [or 33 fluidounces, 6 ½ fluidrachms]. Introduce the drug into a suitable vessel provided with a cover, pour upon it one thousand mils [or 33 fluidounces, 6 ½ fluidrachms] of cold water, cover it well, and boil for fifteen minutes. Then allow it to 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 mils [or 33 fluidounces, 6 ½ fluidrachms"].
"Caution.—The strength of decoctions of energetic or powerful substances should be specially directed by the physician." U. S.
The two decoctions of the U. S. P., 1890, Decoctum Cetrariae and Decoctum Sarsaparillae Compositum, were both dismissed in the Eighth Revision and only the general formula for decoctions retained. See Decoction of Cetraria and Zittman's Decoction.