This section is from the book "Materia Medica And Therapeutics: An Introduction to the National Treatment of Disease", by John Mitchell Bruce. Also available from Amazon: The pharmacology and therapeutics of the materia medica.
Time. The times of the day or night at which the doses must be taken are of the first importance; and speaking generally, it may be said that every advantage must be taken in this respect of the natural tendency which it is desired to assist or stimulate by the drug. Thus, drugs which induce sleep are naturally given at bedtime; alkaline stomachics before meals; saline purgatives early in the morning. The time required by the drug to act must also be calculated, especially in the case of the different purgatives.
7. Combinations: Chemical and Physiological Incompatibles. - In most instances more than one drug has to be given at the same time, and the practitioner finds that he must combine them in a angle prescription, whether, for instance, pill, powder, or liniment. Successful combination is at once the most important and difficult part of the art of prescribing. Whilst it affords the prescriber an opportunity of applying the whole of his knowledge of drugs and their action, it cannot be accomplished without a thorough acquaintance with the physical, chemical, and physiological properties of the ingredients of the proposed compound. The mere appearance, taste, and flavour of a mixture are important points to be considered in ordering it. The chemical reactions which may occur between the constituents must be constantly kept in view. The prescriber may either intend the constituents to remain chemically unchanged, or arrange for the decomposition of one or more of them, and the production of a new substance. Drugs which decompose each other are said to be chemically incompatible in the widest sense; but the use of the term is commonly restricted to instances in which the result is an unexpected, inelegant, useless, or dangerous compound. Thus, if it be desired to give a patient chlorate of potash and hydrochloric acid, we say that the undiluted acid is incompatible with the salt, because chlorine is produced by their combination; but if it be intended to order a fresh solution of chlorine in water, and the decomposition is deliberately planned, the combination would not be considered incompatible. A list of incompatibles will be found under the "characters" of the principal drugs.
The prime consideration, however, will be the physiological effect of the combination. This is very different in different cases. Each of the constituents may be intended to produce an effect different from the others; or to have the same effect; or one or more ingredients may be introduced to modify the action of the principal, that is, to correct some unpleasant, dangerous, or otherwise undesirable influence which it happens to possess, in addition to the influence which we wish to secure. Such correctives are necessarily physiological antagonists, and appear, therefore, to be physiological incompatibles; but it is for this very reason that they are to be combined, because whilst they neutralise the action of each other in certain directions, they are left mutually free to affect other parts of the system. Thus, calomel combined with opium prevents it from causing constipation, whilst it does not interfere with its action on the brain ; and the opium, in turn, prevents the calomel from purging the patient, whilst it allows the mercurial to act as an alterative. Most purgative pills contain correctives or carminatives, which moderate the violence of peristalsis and prevent -pain.
The Prescription. A prescription consists of five parts : The superscription, consisting of a single sign, R, an abbreviation for recipe, "take"; the inscription, or body of the prescription, containing the names and quantities of the drugs ordered ; the subscription, or directions to the dispenser; the signature, or directions to the patient, headed by Signa ; and, lastly, the patient's name, the date, and the prescriber's name or initials. In what may be called a classical prescription, it was customary to arrange the constituents of the inscription under four heads, viz. the basis, or active drug proper; the adjuvant, or substance intended to assist, and especially to hasten, the action of the basis; the corrective, to limit or otherwise modify the same (commonly a carminative); and the vehicle, or excipient, to bring the whole into a convenient, pleasant form for administration.
To take an example:
Ferri et Ammonite Citratis, gr.v. (basis).
Liquoris Ammoniae Fortioris min.jss. (ad-juvant).
Spiritus Myristicae, min.vj. (Corrective).
lnfusi Calumbae, ad ℥i. (vehicle or excipient).
Misce. Mitte doses tales viij.
Signa - Two tablespoonfuls twice a day.
Practitioner's name or initials.
It will be seen that the first three parts of the prescription are in Latin; the signature or directions to the patient in English. The names of the drugs or preparations are in the genitive case, the quantities standing in the accusative case, governed by recipe:
Recipe, Spiritus Myristicce, minima sex.
Take, of Spirit of Nutmeg, six minims.
A few abbreviations and signs are allowed, viz. : R for recipe; m., misce; S., signa; αα., ana (avā), of each;ft., fiat, make; q.s., quantum sufficit, a sufficiency ; αd, up to, to amount to (the full phrase being quantum sufficit αd); c., cum, with; no., numerus, number; p.r.n., pro re nata, as required, occasionally; rep., repetatur, let it be repeated; ss.,fs., semi, or semis, a half.
The names of drugs must always be written in full wherever there can be the smallest possibility of error. It is not only inelegant, but dangerous, to use such abbreviations as Acid. Hydroc. Dil, and Hyd. Chlor.
The various weights and measures are expressed by characters and figures, very rarely by words, placed distinctly at the end of the line occupied by the name of each ingredient; but if two or more consecutive ingredients are ordered in equal quantity, it is usual, instead of repeating this each time, to write it only once after the last of them, preceded by the sign āā, of each.