Administration of Medicines.
Medicines may be introduced into the circulation by various routes, as the gastro intestinal tract, the rectum, the respiratory tract, the veins and arteries, the subcutaneous cellular tissue, and the integument itself.
The Gastro-intestinal Route is the one most frequently employed, being the most convenient. The remedies, after being swallowed, find their way into the current of the circulation, through the walls of the gastro intestinal blood vessels and the lacteals. When the stomach is empty and its mucous membrane healthy, crystalloidal substances in solution pass through the walls of its vessels with great rapidity. Colloidal substances (fats, albumen, gum, gelatin, etc.) require to be digested and emulsified before they can be absorbed.
The Rectum will absorb many substances applied in the forms of Enemata or Suppositories. Those most suited to this route are the salts of the alkaloids in solution, especially those of Morphine, Atropine, and Strychnine, the latter being absorbed more rapidly per rectum than by the stomach. Acid solutions, if not too frequently repeated, are also well administered by this channel.
The Respiratory Tract admits of the rapid absorption of medicinal substances through its extensive blood-supply. The inhalation of vapors or atomized fluids, the insufflation of powders into the nares, fauces, larynx, etc., and the use of a medicinal nasal douche, are methods whereby this channel may be utilized.
The Veins are only used as a route of medication in emergencies, when the other channels are not available and where immediate action is necessary to the preservation of life, the operation being a highly dangerous one. The injection intravenously of Saline Solutions in the collapse of cholera, diabetic coma, etc.,—Blood or Milk as a last resort in excessive hemorrhage, epilepsy, uraemia, the collapse of cholera, etc.—and a solution of Ammonia for the bites of venomous reptiles, Hydrocyanic-acid poisoning, Opium narcosis, Chloroform asphyxia, etc., are the instances admitted in practice.
Arterial Transfusion has also been performed successfully in a number of cases, and is considered safer than venous transfusion when a large quantity of fluid has to be introduced into the circulation. A special apparatus is employed for these purposes, known as Aveling's Transfusion Syringe, but the ordinary Dieulafoy's aspirator slightly modified, may be used with safety and convenience. The danger of the operation lies in the liability of the introduction of air into the circulation, an occurrence which may cause instant death in the human subject.
The Hypodermic Method is the introduction of medicines into the organism by injecting them into the subcutaneous areolar tissue, from which they are quickly absorbed by the lymphatic and capillary vessels.
The medicines must be in solution, of neutral reaction and freshly prepared, the usual menstruum being distilled water; though spring water filtered will answer just as well, and much better than distilled water which has been standing several days, and exposed from time to time to the air. The solution is to be injected beneath the skin, by a hypodermic syringe, care being taken to avoid puncturing a vein. The most suitable localities for the injection are the external aspect of the arms and thighs, the abdomen, the back, and the calves of the legs. On the external aspect of the thigh, just in front of the great trochanter, there is an area of some two inches square, over which the insertion of a fine hypodermic needle is not felt, so barren is the skin in that region of sensitive nerve filaments.
After nearly filling the syringe with the solution to be used, the needle should be screwed on tightly; and with the instrument held in a vertical position, point uppermost, the excess of solution over the amount required should be ejected, thus expelling air—bubbles and filling the needle itself. The needle should then be quickly inserted until its point has passed beneath the skin, when the piston may be pressed down slowly, delivering the solution gradually so as to avoid rupturing the tissue. If the solutions are freshly prepared with clean water, the needles kept clean and sharp, and the injection be made beneath the skin not into it, there will be no risk of producing abscesses with the agents ordinarily employed.
Parenchymatous Injection is the delivery of a medicine deeply into the tissues, either to affect a muscle itself or to locally influence some important nerve-trunk. The principal agents used in this manner are Strychnine for palsied muscles, Chloroform for sciatic and other neuralgias, Salts of Cocaine for local anaesthesia, and Carbolic Acid for deep-seated inflammations.
The Skin is an active absorbent of crystalloidal substances when its epidermis or cuticle is removed. By this route there are four methods of introducing medicaments into the circulation, viz.—the Enepidermic, Epidermic and Endermic Methods, and Inoculation.
The Enepidermic Method consists in placing the medicine in simple contact with the epidermis, no friction being used to hasten its penetration. Solutions of the alkaloids in Chloroform and Oleic Acid pass by osmosis in this manner with comparative ease, but aqueous solutions act very slowly, and alcoholic ones with great difficulty if at all.
The Epidermic Method consists in the use of friction to promote the passage of the medicament between the cells of the epidermis. Mercurial Ointment, Cod liver Oil, and other fats, Oleates, etc., are used in this way for their local and systemic effects.
The Endermic Method obviates the difficulty of absorption through the cuticle by removing the latter through the agency of a blister, and then powdering the medicament over the surface of the denuded derma.
An ordinary cantharides-plaster, followed by a poultice to raise the blister, may be employed but a quicker method is to place upon the skin a piece of lint soaked in Stronger Water of Ammonia, covering it with a watch-glass or a piece of oiled silk to prevent evaporation. The blister raises rapidly and should then be removed with scissors. Morphine, Atropine, Quinine and Strychnine, are the agents generally used in this manner, but the method is painful and unpopular.
Inoculation is the introduction of medicinal agents through the scraped or punctured skin by an operation similar to that employed for vaccination.
A Compend of Materia Medica, Therapeutics, and Prescription Writing, 1902, by Sam'l O. L. Potter, M.D., M.R.C.P.L.