Infusions are prepared by macerating drugs in distilled water for short periods of time, varying from fifteen minutes to two hours. The volume of the product is indefinite, and depends upon the quantity of menstruum retained by the marc, which should not be pressed. The method of disintegration to which the drugs are subjected, the temperature at which infusion is commenced, and the period of maceration depend upon the nature of the drug and the substances to be extracted. Infusions should be prepared in earthenware vessels, thoroughly warmed before use. For the preparation of infusions possessing no marked therapeutic activity, a measured quantity of boiling distilled water is usually poured into the warm vessel, containing the drug. In the case of potent infusions (such as infusion of digitalis or infusion of ergot) exactness may be ensured by weighing the boiling menstruum into a tared vessel containing the. requisite quantify of drug. When preparing infusions the material to be extracted is either suspended by some suitable contrivance immediately below the surface of the menstruum or placed at the bottom of the vessel. In the latter instance the contents should be occasionally stirred, and finally strained. If the medicament is tied in a piece of muslin and suspended immediately below the surface of the menstruum, extraction ensues by the process of circulatory solution, and the marc can be removed without straining. It is important to remove the marc from infusions as soon as the period of maceration has elapsed, and it is usually necessary to allow the preparations to cool before use. Drugs containing an active principle which is easily soluble in cold water (such as quassia wood), and those containing an appreciable quantity of starch (such as calumba root) are prepared with distilled water at ordinary temperature. Infusions are generally employed as diluents, and as vehicles for the administration of substances in the form of mixtures, by virtue of either aromatic or bitter principles. They are principally useful as flavouring agents, adjuvants, or correctives. Infusions should be freshly prepared as required where possible. Infusions which are constantly ordered, such as compound infusion of gentian and infusion of senega can be preserved by sterilisation, A convenient quantity sufficient for a week's supply may be prepared and poured into narrow necked bottles of convenient size, the bottles should be filled to within half an inch of the tops, immersed to the necks in a water-bath, and the water raised to the boiling point for ten minutes. The necks of the bottles should be tightly plugged with cotton wool, and the source of heat removed. Infusions may be safely preserved by this method for at least a week, irrespective of the prevailing temperature, and for longer periods if the bottles are closed with accurately fitting glass stoppers, secured with a covering of animal tissue. If this method of preservation is restricted to those infusions which are frequently required and the quantity sterilised is not more than is sufficient for about a week's supply, there is no risk of change in the preparation during such a period. Infusions for which special formulae are not given, and for which there is no stated strength, may be prepared by placing 5 of the drug, in coarse powder, in a suitable covered vessel, adding 100 of boiling distilled water, allowing the infusion to stand for fifteen minutes in a warm place, and straining.
Concentrated infusions are preparations which, when diluted with seven times their volume of distilled water, yield products representing approximately the corresponding infusions of the British Pharmacopoeia. Similar preparations have been used largely as substitutes for fresh infusions in cases of emergency, but the official Liquores Concentrati, which are preparations analogous to so-called "concentrated infusions," were introduced with the intention that medical men should prescribe them in place of the unofficial preparations. Those products, however, have not been received with favour, and the processes here described are recommended as yielding preparations of a more satisfactory character.
The Macero-Expression Process.—Macerate the solid ingredients in 75 of the menstruum in a covered earthenware vessel for twenty-four hours, using slight pressure when the whole of the drug is not covered by the menstruum. Strain, if necessary, and press the marc.
To the resulting liquid add the other ingredients specified in the monograph, and reserve. Repeat the above process a second and a third time for six hours each. Evaporate the weaker pressings over a water-bath, until the volume of the resulting liquor together with that of the reserved portion equals 100. Set aside for seven days, then filter. When diluted alcohol is used as a menstruum, the third maceration may be omitted, and for the second maceration only enough menstruum should be employed to make the expressed liquids, when united, measure 100. The diluted chloroform water is prepared by, dissolving 1 mil of chloroform in a litre of distilled water. This is to be used not only when diluted chloroform water is directed to be employed as a menstruum, but also in the production of the diluted alcohol used for the same purpose.
The Repercolation Process.—Moisten one-half of the solid materials with sufficient menstruum to form a damp powder, set aside in a covered vessel for two hours, or until thoroughly swollen, then pack in a percolator and percolate slowly with the menstruum. Moisten the rest of the drug with the first portion of the percolate, and, after standing for two hours, pack this in a second percolator, and, employing the first percolate as a menstruum, allow percolation to proceed slowly until the second percolate measures 60. To this add the alcohol and any tincture included in the formula, and reserve. Allow percolation to proceed until the marc is practically exhausted, collecting, if necessary, another 100 of percolate. Evaporate this over a water-bath to small bulk, mix with the reserved portion, and add, if necessary, sufficient of the menstruum to make the volume of the final product up to 100. Set aside for seven days and clarify. When diluted alcohol is the menstruum, percolation should only be carried on until too of percolate has been collected from the second percolator.