Infusa. U.S. Infusions.
Apozemes, Tisanes, Infusions, Fr.; Infusa, P. G.; Infusionen, Aufgüsse, G: Infusi, It.; Infusiones, Sp.
These are aqueous solutions obtained by treating with water (without the aid of ebullition), vegetable products only partially soluble in that liquid. The water employed may be hot or cold, according to the objects to be accomplished. Infusions are generally prepared by pouring boiling water upon the vegetable substance and macerating the mixture in a tightly closed vessel until the liquid cools. The soluble principles are thus extracted more rapidly, and, as a rule, in a larger proportion, than at a lower temperature. Some principles, moreover, are dissolved in this manner which are nearly or quite insoluble in cold water. A prolonged application of heat is in some instances desirable, and this may be effected by placing the vessel near the fire. Cold water is preferred when the active principle is highly volatile, when it is injured by heat, or when any substance of difficult solubility at a low temperature exists in the vegetable, which it is desirable to avoid in the infusion. A longer continuance of the maceration is necessary in this case, and in warm weather there is sometimes danger that spontaneous decomposition may commence before the process is completed. When a strong infusion is required, the process of percolation may be advantageously resorted to. The water employed should be free from saline impurities which frequently produce precipitates and render the infusion turbid. Fresh river, rain, or distilled water is usually preferable to water pumped from wells or obtained from springs, except when the latter are known to produce water which will not react with any of the constituents of the infusion.
The substance to be acted on should be sliced or bruised, or in the state of powder, but this last condition is seldom requisite, unless when percolation is employed, and is always inconvenient, as it requires that the infusion should be filtered through paper in order completely to separate the undissolved portion. In other cases it is sufficient to strain it through fine linen or muslin. When percolation is resorted to, the substance should be more or less finely powdered. The United States Pharmacopoeia furnishes a general formula for infusions, which is to be used when the proportions are not specified. In the U. S. P., 1880, the strength of such infusions was fixed at 10 per cent. Experience has shown, however, that this was too strong for general purposes, and in the U. S. Pharmacopoeia of 1890 and the Eighth and Ninth Revision, 5 per cent. has been chosen as the limit.
General Formula for Infusions, U. S. P. IX.
"Infusions must be freshly made from the drugs, and, when the strength of Infusions 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 fluid-ounces, 6 ½ fluidrachms]. Introduce the substance into a suitable vessel provided with a cover, pour upon it one thousand mils [or 33 fluidounces, 6 ½ fluidrachms] of boiling water, cover the vessel tightly, and allow it to stand for half an hour. Then strain with expression, and pass enough water through the strainer to make the Infusion measure one thousand mils [or 33 fluidounces, 6 ½ fluidrachms]. If the activity of the Infusion is affected by heat, cold water only should be used.
"Caution.—The strength of Infusions of potent or very active drugs should be specially directed by the physician." U. S.
Infusions are usually prepared in glazed earthenware or porcelain vessels fitted with covers. Brande suggests the use of clean metallic vessels, which, when finely polished, retain the heat for a longer time, but they are more liable to chemical alterations, and may sometimes injuriously affect the preparation. Vessels of block-tin are generally well adapted for the purpose.
As infusions do not keep well, especially in warm weather, they should be made extemporaneously and in small quantities. In this country they are usually prepared in the patient's home, and the propriety of their introduction into the Pharmacopoeia has been doubted, but it is desirable to have certain fixed standards for the regulation of the medical practitioner, and it is always preferable to direct infusions from the apothecary, for whose guidance official formulas are necessary. Physicians would, indeed, find an advantage in more frequently directing them to be prepared by the pharmacist, instead of leaving their preparation to the carelessness or want of skill of attendants upon the sick. Infusions may be kept during hot weather, and for many months, by straining them while hot, and pouring them at once into bottles provided with accurately ground stoppers. The bottle must be brim-full, the stopper being made to displace its bulk of the fluid. A common bottle with a cork stopper may be used, if the softened cork be forced into the full bottle, tied down, and at once dipped into hot sealing wax. The hotter the liquid and the freer from the air the better will the infusion keep. Sterilization of infusions by heating them to the boiling point, then preserving in bottles which have been kept hot to destroy germs, and stoppered with sterilized cotton, is effective, particularly if the bottles have a stopcock near the bottom to draw the infusion when wanted. Almens has proposed a very efficient method of preserving infusions. (A. J. P., April, 1875.) It is as follows: The infusion or decoction is heated for some time in a water bath at 100° C. (212° F.), and the bottle is then fitted with a tight cork, through which a glass tube passes lightly filled with cotton wool. The cork has a second opening, through which a glass tube passes nearly to the bottom of the bottle; this tube is bent at a sharp angle and has fitted to it a piece of India rubber tubing, to which a pinchcock is attached, by means of which the contents may be drawn as wanted. By making very concentrated infusions, as suggested by Donovan, with a mixture of three parts of water and one part of alcohol, they may be long kept, and when used can be diluted with water to the proper strength. Thus, if made four times as strong as the official infusion, they may be diluted with three measures of water. The proportion of alcohol would thus be very small, but it might still be medicinally injurious, and infusions should not be prepared in this way unless with the cognizance of the prescriber.
Battley, of London, introduced a set of preparations, which he called inspissated infusions, the advantages of which are that the virtues are extracted by cold water, are not injured by heat used in the evaporation, are in a concentrated state, and are not impaired by time. To prepare them he macerated the material, coarsely powdered, bruised, or finely sliced, in twice its weight of cold distilled water, pressing the solid matter into the liquid repeatedly by a rammer or the hand; then allowed the liquid to drain out, or expressed it in the case of highly absorbent substances, and repeated the process, with an amount of water equal to that which had been separated, until the strength was exhausted. Four or six hours of maceration were usually sufficient. The infusion is then to be concentrated by evaporation, at a temperature not exceeding 71.1° C. (160° F.) to the sp. gr. 1.200, and as much alcohol is to be added as will make its sp. gr. 1.100. These preparations are very analogous to the fluidextracts already considered. As a rule, it would probably be preferable to prepare infusions by the process of percolation.
The inspissated infusions must be diluted when administered. The presence of alcohol, though in small quantity, would sometimes be a serious objection. (P. J., x, 129.) Concentrated infusions of the strength of 50 per cent. were introduced into the British Pharmacopoeia (1898); they are mostly made by percolation, and were termed "Liquors." This certainly led to confusion in nomenclature, and it is difficult to understand why they were not called concentrated infusions, particularly as then- almost universal use is for making ordinary infusions by diluting with water. They were dropped from the British Pharm. 1914.