This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol1", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
Laudanum is prepared, according to the U. S. Pharmacopoeia, by-macerating two ounces and a half of powdered opium first, for three days, with a pint of water, then, for three days longer, with the same menstruum increased by the addition of a pint of alcohol; submitting the whole to percolation; and, when the liquid ceases to pass, pouring in diluted alcohol, until two pints of tincture are obtained. When it is properly made, the virtues of the opium may be considered as wholly extracted by the menstruum. The pulverization of the opium ensures the previous drying of the drug, which is important; for crude undried opium always contains water, and often in considerable though variable proportion; and, if it were employed in the process, would render the resulting tincture weaker than the officinal, and of uncertain strength. Happily, though the British process differs somewhat from our own, the resulting tincture is so nearly the same, that the two, for all practical purposes, may be considered as identical. Laudanum should be kept in well-stopped bottles, as the alcohol evaporates on exposure, and the liquid is rendered turbid by the deposition of the dissolved matter. Not unfrequently flakes of solid extract may be seen at the bottom of old laudanum bottles; and it may be readily conceived that, if this should be dropped out with the liquid, the narcotic effects of it would be very greatly increased. Death in infants has resulted from this cause; and I suspect that the cases of unexpectedly violent effects in young children from a drop or two of laudanum, which we find related by writers, might, if carefully investigated, have been traced to this cause. Every practitioner should be aware of this fact, and guard against the use of laudanum rendered turbid by evaporation, especially when prescribing for the very young.
This tincture is very much used for obtaining the effects of opium, the properties of which it may be considered as fully representing. It has the advantage of operating more quickly than the opium in substance, and of facilitating the exhibition of the medicine in minute doses; but it is sometimes less acceptable to an irritated stomach, probably in consequence, in part, at least, of the alcohol it contains. The same cause renders it less suitable than the infusion of opium, or a solution of the extract, for application to tender surfaces, as to the conjunctiva, rectum, urethra, and even sometimes the skin, when highly irritated or inflamed.
The dose of laudanum equivalent to a grain of opium is thirteen minims, or about twenty-five drops. It should be remembered that a flui-drachm or teaspoonful contains on the average about 120 drops, and that one minim is about equal to two drops. The mistake has often been made of directing a teaspoonful of laudanum by enema, under the impression that it contained only 60 drops, or between twice and three times the amount of the ordinary dose by the mouth, whereas it is about quintuple that dose. Hence, profound narcotism has often been induced, when only gentle sleep was wanted. I have known of a fatal case of coma, occurring immediately after an enema of laudanum, and have not been without my suspicions that this was the cause of death. Not more than fifty or sixty drops should be given at first by injection. Tincture of opium is often used as a local anodyne; being employed as a lotion, or added to cataplasms, or in conjunction with other anodynes or with rubefacients in the form of a liniment. It may be added to the common soap liniment (Linimentum Saponis,U. S., Br ), in the proportion of one part by measure to three, according to the late London Pharmacopoeia, or in equal measure according to the British; and this mixture is usually called the Anodyne Liniment (Liniment of Opium, Linimentum Opii, Br.). Laudanum may be introduced into the external auditory meatus, or into the cavity of a carious tooth, upon a little raw cotton. From five to ten drops of it in a fluidounce of water may be inhaled in the form of spray, in irritative affections of the throat and lungs.