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.
B. Subcutaneously (hypodermatically), the drug being introduced beneath the skin by means of a special hollow needle and a syringe. To be used thus, a preparation must be in liquid form, and, as a rule, in complete solution; though in some instances, as in the use of insoluble mercury salts, the drug may be in the form of a fine powder held in suspension in oil. A substance for hypodermatic use must be capable of complete absorption, or it will act as a foreign body; and must be in small quantity, because large amounts will produce too great separation of the tissues. Irritant drugs are only occasionally given hypodermatically, both because they are painful and because they may produce necrosis of cells with abscess formation. Such abscesses are sterile, however, as they are not caused by pathogenic bacteria.
For convenience, many drugs are put up in the form of tablets called hypodermic tablets. They are made of the drug and finely powdered cane-sugar mixed together, moistened with alcohol, and forced into molds. When dry, they can be handled without disintegration, but are readily soluble. (Tablets made by compression do not dissolve so easily.) Hypodermic tablets of salts of morphine, atropine, strychnine, etc., can be carried in a pocket-case; when wanted, they may be placed in the syringe and dissolved there in sterile water drawn up to make the solution, or may be made into a solution with a few drops of water in a spoon. For sterilization the water may be heated in a spoon over a spirit-lamp or a gas-burner. Drugs dissolved in normal salt solution (0.9 per cent. NaCl) tend to be less irritant to the tissues and more readily absorbed than those dissolved in plain water, but when the total amount of the solution is very small, tap-water will do.
To give a hypodermatic injection, the dose is placed in the hypodermic syringe (many liquids cannot readily be drawn up through the syringe needle), the sterilized needle (it may be sterilized in a test-tube or spoon) is screwed on, and the syringe is turned needle upward so that any bubbles of air may be driven out by pressure on the piston. Thin liquids may be drawn directly into the syringe through the needle.
There are two methods of injection for systemic effect, the subcutaneous and the intramuscular. In the subcutaneous method the properly cleansed skin, usually of an arm or a leg, is pinched up between the thumb and finger of one hand, while the needle is quickly plunged in a slanting direction through the skin into the subcutaneous tissue. In the intramuscular method the needle is plunged straight through the skin and subcutaneous tissue into the underlying muscle, usually in the back, buttocks, or chest, though sometimes in the limbs. This method favors ready absorption. By either method, a sharp needle and quick puncture give almost no pain. The fluid is slowly injected, the needle is quickly withdrawn, the point of the puncture is covered to prevent the fluid from running out, and the spot is gently massaged to promote diffusion of the liquid into the tissues. The hypodermatic needle may be cleansed by first forcing water through it, and then allowing a few drops of alcohol to descend through it by capillarity. A fine wire drawn through the lumen keeps it permeable. (In the introduction of cocaine and similar drugs for local anesthesia where a local action only is desired, the needle is inserted just beneath the epidermis and gives a superficial subcutaneous injection, or an intracutaneous injection. This method is not used when a systemic effect is desired.)
There are certain advantages and disadvantages in hypodermatic medication.
The advantages are:
1. Certainty of action - all the drug gets into the tissues; therefore the dose is more definite.
2. Rapidity of action - because the drug in most instances quickly reaches the circulation by means of the capillaries or lymphatics.
3. Availability - when administration by mouth is not feasible, as when (1) the patient cannot swallow, as in unconsciousness; or (2) will not swallow, as in drunkenness or delirium - or when drugs are taken with suicidal intent; or (3) the alimentary tract is in a state of intolerance and non-absorption, as in uncontrollable vomiting or diarrhea. The disadvantages are seldom encountered. They are:
1. The chance of abscess formation, either a sterile abscess from an irritant drug, or an infective abscess from un-sterile solution, needle, or skin.
2. The chance of injecting the drug into a vein. This would plunge the whole dose into the circulation at once, perhaps with disastrous results. To avoid this the syringe may be unscrewed from the needle; if blood oozes from the needle, this is withdrawn and inserted elsewhere.
3. The chance of injecting the drug into a nerve, with resulting great pain and even paralysis.
Hypodermatic medication has a very restricted employment, because only those drugs whose dose in solution is of small bulk are available for this method of administration.
C. By hypodermatoclysis, in which a large quantity of saline liquid (50 to 1200 c.c.) is injected into the loose tissues about the breasts or abdomen, or into the back below the scapula, or into the buttocks or thighs. The liquid is allowed to run in slowly by means of a funnel or reservoir and rubber tube attachment to the needle. If the fluid is not isotonic, or nearly so, with the blood, or if it interferes by pressure with the circulation of the part, it may result in gangrene or abscess. The writer has seen extensive gangrene follow the injection of 200 c.c. of 2 per cent. solution of sodium carbonate in a diabetic.
Drugs may be placed in the rectum by means of an enema, i. e., a rectal injection, or in the form of a suppository or ointment. The uncertainty of absorption and the chance that the drug will be expelled limit the usefulness of this channel and largely restrict it to drugs for local effect only. Proctoclysis is a rectal irrigation or injection intended for both local and systemic effect. It is usually made with saline or medicated saline fluids. (See Rectal Treatment, Part II.)
E. By the skin, by inunction, in which an oily or fatty preparation is rubbed upon the skin and left to be absorbed. On account of uncertainty of absorption the dose may vary within wide limits. Mercurial ointment is so used in the treatment of syphilis, and cod-liver oil and cocoa-butter in the treatment of malnutrition.
Drugs administered by a vein act with great promptness, the whole dose passing at once into the circulation. Intravenous medication may be by injection or by infusion. In intravenous injection the drug, diluted with a small quantity of normal salt solution, is injected from a syringe, the needle being plunged through the wall of the vein in a slanting direction and toward the heart. When the needle is withdrawn, the valve-like opening thus made usually closes of itself, though sometimes there is a moderate extravasation of blood into the tissues. In intravenous infusion a large quantity of warm normal saline solution (500 to 1500 c.c), or some isotonic liquid, with or without the addition of drugs, is slowly passed into the vein through a suitable nozzle. This requires tying a vein, so it cannot be repeated more than once or twice, and is employed only in emergencies.
G. Through the lungs by inhalation - of gas for absorption into the system, as in the use of chloroform or ether as a general anesthetic. (Inhalations of medicated vapors are employed also for a local effect on the respiratory organs.)