This section is from the book "Materia Medica: Pharmacology: Therapeutics Prescription Writing For Students and Practitioners", by Walter A. Bastedo. Also available from Amazon: Materia Medica: Pharmacology: Therapeutics: Prescription Writing for Students and Practitioners.
The subject of the materia medica is an extensive one, and the text-books contain many things that the physician does not need to know. He need not learn the pharmacopeial definition, where and how a drug grows, the method of its collection, its physical and microscopic characters, its preparation for the market, its adulterants, the process of manufacture of chemic drugs, the shapes of crystals, melting-points, etc. Such data are for the pharmacist, the chemist, and the pharmacognosist, the men upon whom the physician must depend for his proper supply of good drugs.
But as physicians we need to know the following:
In prescriptions we use the Latin names only, but in the literature find both the English and the Latin, so we must know both. We learn, therefore, that ficus is fig, and zingiber is ginger, and rhamnus purshiana is cascara, and mistura cretae is chalk mixture. (See also Use of Latin in chapters on Prescription-writing.)
Of particular importance are those active constituents which are isolated from the drug and used by themselves in medicine, as morphine, strychnine, salicin, menthol, etc., or those which make undesirable incompatibles, as tannic acid.
3. The solubilities and incompatibilities of chemic drugs and of active constituents, where these become of importance from a prescription or utility point of view.
These are the official preparations, and such unofficial ones as are in common use. To know at least some of them is essential to the writing of prescriptions, for not only are the official preparations the ones that are made of uniform strength throughout the United States, but they are the forms in which a remedy can be conveniently obtained.
The average dose is given in the Pharmacopoeia, and this, in most instances, is the dose to learn; and since what is desired for the patient is a therapeutic dose of the drug itself, the dose of the preparation should be such an amount as will represent the desired dose of the drug. The learning of doses is greatly facilitated by the pharmacopeial custom of having one strength for all the more powerful preparations of a given class. For example, all fluidextracts are of 100 per cent. strength; therefore their dose is that of the drug, but in liquid measure, i. e., each cubic centimeter is equivalent to one gram of the drug. All potent tinctures are of 10 per cent. strength, so their dose is 10 times that of the fluidextract. Most extracts approximate 5 times the strength of the drug, hence have a dose of one-fifth as much. For preparations, therefore, the doses do not have to be carried in mind as separate things, but can be instantly calculated from the percentage strength if the dose of the drug itself is known. On account of pharmacopeial uniformity, the percentage strength is easily learned, as shown above. As an example, take the preparations of digitalis; if the dose of digitalis is taken as 1 grain (0.06 gm.), that of the fluidextract is 1 minim (0.06 c.c), that of the 10 per cent. tincture is 10 minims (0.6 c.c), and that of the 1.5 per cent. infusion is 67 minims, or approximately 1 dram (4 c.c). These amounts of the specified preparations each represent the dose of 1 grain of digitalis.
How the drug acts. This includes the expected or usual action and any unusual actions, from both therapeutic and toxic amounts.
An extensive subject of immediate practical importance to every physician, to be studied in a general way with pharmacology, but to be studied in greater detail in connection with the individual diseases. It is in therapeutics that there is so much of the traditional, the old-fashioned, the empiric; and the crying need of the medical profession is that drug therapeutics shall be based directly upon thorough pharmacologic knowledge tried out by clinical tests.
How best to prescribe or administer the remedy.
Conditions in which the drug is dangerous, or may be prescribed only with special caution.
Indication is a term used in medicine for the kind of treatment "indicated" or "pointed out" by the symptoms or disease of the patient. We say, for example, that "the indications in such a sickness are that the patient shall remain in bed, on a milk diet, and shall have a dose of calomel." Or, to put it in another way, we say that "rest in bed, a milk diet, and calomel are indicated," i. e., "pointed to" by the symptoms as the means of treatment to be employed. Contraindication has the opposite meaning; it is a condition in which the drug should not be employed.