Strychnine gr. 1/50 is called for, the solution on hand has a strength of 1%
Since e 100 contains gr. i.
. . e I " "1/100.
.. gr. 1/50 will be contained in as many minims as grain 1/100 is contained in gr. 1/50.
1/50 % 1/100 = 1/50 * 100/1 = 2
Minims 2 of the stock solution represents the amount called for, viz., gr. 1/50.
The foregoing examples would hold good for modification of doses if given by the metric system.
To illustrate the procedure under these conditions the following example may be given:
Codeine tablets gram 0.06 on hand.
Dose required gram 0.015.
Demonstrate the ratio of 0.06: 0.015, viz. .4. .4 (2/5) of the .06 gram tablet will then be needed to make the dose called for, viz. 0.015.
Estimation of child's dose.
To estimate the proportional dose for a child under twelve years from the adult dose, proceed as follows:
Make a fraction by taking the child's age as the numerator and the child's age plus 12 as the denominator. Divide the adult dose by the resulting fraction.
Dover's powder grs. x represents adult dose.
Dose for child of 3 years required.
3 / 3+12 = 3/15 * 10/1 = 2
Dose for child of three years would be grs. ii.
We find the metals, as prepared for medicinal use, usually in solution, after being changed in form by the action of various other chemical agents. Among tinctures, on the other hand, are found many of those vegetable drugs from which are obtained the powerful alkaloids. But if the pure alkaloids alone are desired, as they are insoluble in water and only partly so in alcohol, they must be treated as the metals are, and combined with an acid to make them ready for ingestion. In this combination both metals and alkaloids form what are called "salts" - being perfectly soluble in water yet retaining all their medicinal qualities. Thus one reads of the "salts" of iron, the "salts" of strychnine, etc. Various acids are used, but the most common one is sulphuric acid, as it is cheap. These salts are then finally prepared for use in solution, and distinguished from each other by the name of the acid used - e. g.,"the solution of the sulphate of morphine," the "hydrochloride of cocaine," etc.
As solutions are made in varying strengths, the face of the bottle is always carefully marked either with the percentage or with the amount to the drachm.
Many preparations of drugs are injured by age, especially when not securely corked. Tinctures and fluid-extracts become stronger by reason of evaporation of their alcohol. Infusions soon spoil. Many preparations are injured by light and air, as the silver solutions, and others are unstable as to composition.
Medicinal agents may be applied: (1) to the skin in various ways, viz., by inunction, as oils, liniments, and ointments, rubbed into the skin; by simple contact without rubbing, as medicated baths, cooling or sedative mixtures, blisters, plasters, powders, etc.; and by painting, as iodine; (2) to mucous membranes, as gargles, insufflations, sprays, and douches; (3) to wounds and diseased tissue, as antiseptic powders, ointments, and solutions; or they may be administered (4) by inhalation, as fumes or vapor; (5) by hypodermic injection into the subcutaneous tissues; (6) by the mouth, or by the rectum, into the alimentary canal.
By the first three ways, the effects produced are, generally speaking, local (though in many instances the local impression may be deepened into a general one) and results are slow.
Inhalation is a rapid mode of impressing the system, but only a few drugs are fitted for use in this way.
Drugs given hypodermically act most promptly, because they go directly into the blood current, and are diffused through the tissues in a short time. Only highly concentrated or powerful agents which are active in small bulk can be given in this way; and of these, many, otherwise available, are forbidden on account of their irritant properties.
Medicines are most often given by way of the alimentary canal, and the rectum is used when for any reason it is not desirable to use the stomach.
Having entered the circulation by whatever route, a drug is carried by the blood to the tissues, and is finally eliminated, or cast off as waste product, by the excretory organs.
As full instructions for giving hypodermic injections are found in nursing text-books, only brief details of the methods used for deep and superficial injections are here given.1 The measurements commonly used in this country are the minim - e, the fluid drachm - ʒ, and the fluid ounce - ℥, or half ounce - ℥ ss.
The minim is not by any means the exact equivalent of a drop, nor are all drops alike. A medicine ordered in minims must not be measured by drops, nor one ordered in drachms, by a teaspoon.
It is hardly necessary to say that the nurse should always know what she is giving, and in what proportions. It is therefore essential that she should learn to read prescriptions, to recognize the most important ingredient or ingredients contained therein, and to find out by arithmetical process the exact amount of such ingredients contained in a given dose.
In order to facilitate the learning of doses it may be advisable to become familiar with the ordinary dose of the different classes of drugs.
xv. (0.3-1 mil), except the tincture of iodine, which is given in doses of ei.-iii. (0.05-0.2 mil).
xx. (0.65-1.3 mils). Potent fluidextracts are given in doses of ei. (0.05 mil).
Solid extracts may be administered in gr. i. (0.06
1 Pages 278-280.
Gm.) doses. The potent solid extracts are given in gr. 1/4 (0.015 Gm.) doses.
Spirits may be given in doses of ʒ ss. (2 mils), except the spirits of nitroglycerin ei.-iii. (0.05-0.2 mil), and the spirits of phosphorus ex. (0.65 mil).
Syrups are given in doses of ʒ i. (4 mils); the syrup of the iodide of iron in doses of ex.-xxx. (0.65-2.0 mils).
xxx. (0.65-2.0 mils), well diluted and taken through a glass tube. Dilute hydrocyanic (prussic) acid is taken in doses of e i.-iii.(0.05-0.2 mil).
Infusions and decoctions range in dose from one to two tablespoonfuls (15-30 mils). Infusion of digitalis is taken in doses of ʒ i.-iv. (4-15 mils).