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.
For three obvious reasons the writing of prescriptions is the dread of the young medical practitioner. The reasons are: (1) His fear that he may not express his desires correctly; (2) his distrust in his ability to make satisfactory combinations or palatable mixtures; and (3) his anxiety lest a faulty construction should make him the subject of the pharmacist's criticisms.
A prescription (prae, scriptum, written for) is a physician's order to the pharmacist directing him to furnish for a patient one or more remedies dispensed in some special form. The first essential, therefore, in prescription writing is clearness of meaning, so that the pharmacist will, without any doubt, understand correctly the physician's desires. Important on the part of the physician is familiarity with weights and measures, the symbols employed in prescription-writing, and, to some extent, Latin construction and case-endings. A table of weights and measures is to be found in Part I. The symbols employed and the methods of expressing amounts are as follows:
In metric prescriptions the amounts are expressed by simple abbreviations and Arabic numerals, with fractions expressed as decimals, e. g., gm. 6.5, c.c. 0.6. In the United States it is understood that solids are weighed and liquids measured, so that the terms gm. and c.c. may be omitted. An excellent way of avoiding the writing of periods, which occasionally, in hurried writing, may resemble the figure 1, is to draw a vertical line and place to the left of it all whole numbers referring to grams or cubic centimeters, and to the right of it all fractions. Thus, in the following formula, three ways of expressing the amounts are shown, viz.:
Massae ferri carbonatis............
Misce et fiant capsular No. xxx.
In prescriptions of the apothecaries' system the amounts are expressed by certain special symbols and Roman numerals. The symbols commonly employed are: gr. = grain or grains; gtt. = drop or drops; m = minim or minims; Э = scruple or scruples; 3 = dram or drams; = ounce or ounces; lb.
= pound or pounds; O = pint or pints (from octavius, one-eighth of a gallon), and Cong. (Congius) = gallon or gallons. As solids are weighed and liquids measured, it is superfluous to prefix f before the dram and ounce signs, as f3 , to indicate flui-dram, fluidounce. The symbol for scruple Э is dropping out of use because in written prescriptions it has frequently been mistaken for 3 (dram).
In printing Roman numerals of prescriptions small letters are employed as: iv = 4, xlviii = 48. In writing, small letters are used for one (i or j), five (v), and ten (x), and capitals for 50 (L), 100 (C), and 1000 (M); and it is customary to draw a line above all the letters making up the number, the dots of i and j being put above this line; for example, In a number with terminal one, as one, two, three, seven, or eight, the last letter is printed j, or written as i with a stroke projecting below the line, e. g., ij, iij, vij. This is to signify that it is terminal. Errors have been made because of a comma inadvertently added, and even because of some mark, such as a fly-speck, upon the paper. The dot over the terminal one is an additional check; for if all the letters i and j are not dotted, the pharmacist may be in doubt as to the number intended. As v, x, 1 and c are not dotted letters, it is incorrect to place dots over them.
In expressing fractions in the apothecaries' system, one-half is printed ss, and written ss or s, the manuscript double s. It is an abbreviation of the Latin semis. Other fractions are written in Arabic numerals as vulgar fractions, e. g., 1/3, 1/5, 1/8. Fractions other than one-half are not employed with terms other than grain or minim. Thus, while 3iss is good usage, 3i 1/5 is not, and should be expressed as 3i gr. xii, or as gr. lxxij.
A typical example of an ordinary liquid prescription is:
For Mrs. Wilson, April 20, 1913.
Bismuthi subnitratis ..........................................
q. s. ad iij
M. et Sig
3 ij with a little water every three hours.
W. M. Johnson, M.D.
Interpreted, this would read: Take two drams of the sub-nitrate of bismuth and a sufficient quantity of chalk mixture to make the total measure three ounces, mix them together (according to the art of pharmacy), and on the label write, "Two tea-spoonfuls with a little water every three hours."
According to custom, a prescription is written in six sections, viz.:
1. The name of the patient and the date. (The name is omitted from a prescription for venereal disease, or where it is best for esthetic reasons, as in prescribing a vaginal douche.) The pharmacist is expected to put the name of the patient on the label, but unfortunately does not always do so. It is important if there is more than one patient in the family. The name is also a check on the pharmacist, in case he should send the wrong bottle.
2. The symbol (pronounced R X, but always written as a capital R with the tail crossed). This is placed at the upper left-hand corner preceding the names of the ingredients. It is used at present as an abbreviation of the Latin word "Recipe," the imperative of the verb recipio, I take. It means, therefore, "Take thou," and is always followed by the accusative case.
3. The name and quantity of each ingredient. The quantity may be a weight, a measure, or a number.
4. Directions for compounding - whether the pharmacist shall simply mix the ingredients (M. or Misce), or make them into an emulsion, or into pills, or capsules, or a plaster, etc.
5. Directions for the label - to be placed there by the pharmacist. These are always preceded by the term S. or Sig., which is an abbreviation of the Latin imperative signa, meaning write or label.
6. The physician's signature.