Antidotes, (anti , against, didwmi , I give),—are agents which act upon poisons in such a manner as to alter their composition, rendering them more or less innocuous, and so preventing their toxic action being exerted upon the organism. Antidotal action takes place in the alimentary canal, upon such portion of the poison as is unabsorbed, and is applicable to vegetable as well as to mineral poisons. Antidotal Measures are such medicinal or mechanical processes as tend to remove a poison from the body, either before or after the use of an antidote; and include Emesis, the use of the Stomach pump, Purgation, etc. The term Antidotal Treatment covers the employment of both antidotes and antidotal measures, and is often used in a still wider sense, namely, to mean all the treatment of a case of poisoning, including the use of Antagonists as well as that of Antidotes.
Antagonists,—are agents which directly oppose each other, in some or all of their physiological actions, and therefore may be used, one against the other, in a case of poisoning by either, to counteract its effect upon the organism, after it has been absorbed, and when, therefore, the time for an antidote has passed. Antagonistic action takes place in the blood and tissues, and is applicable almost entirely to vegetable poisons. Antagonistic Measures are such mechanical procedures as tend to the same end, the antagonism of the effects of poisons, and include Artificial Respiration, Faradism of certain muscles, Douching, Motion, Rest, etc.
For example, in a case of poisoning by Digitalis, the antidote would be Tannic Acid, because it forms with the active principle of Digitalis a compound, (Tannate of Digitalin), which is not readily soluble, and is therefore comparatively innocuous. But as this new compound is not wholly inert, it must be removed from the body; an antidotal measure is, therefore, employed, viz. Evacuation of the Stomach,—which may be accomplished by the administration of Zinc Sulphate or any other emetic, or by the use of a stomach. pump.
But, supposing that sufficient time had elapsed, between the ingestion of the poison and the administration of the antidote, for some degree of absorption to have occurred, and that we observe evidences of the presence of the poison in the blood, we must resort then to an antagonist. Now, Aconite and Morphine antagonize the cardiac action of Digitalis, but Saponin and Senegin are its most complete antagonists, their counteraction extending throughout the whole range of its physiological effects. Having made our selection, we would use one of these agents cautiously, being careful not to substitute its toxic actions for that of the original poison; and we would aid its influence by enjoining absolute Rest in the recumbent posture, which is an antagonistic measure of great importance against the effects of Digitalis upon the heart.
In most cases of poisoning by powerful vegetable drugs assistance is not obtained until absorption has proceeded so far that antidotes are of little value, and the chief reliance must be placed upon the appropriate physiological antagonist, and such supporting measures as will sustain the action of any vital function which shows signs of failing. In this way we endeavor to maintain life until the excretory functions of the organism have had time to eliminate this poison by way of the natural channels.
Under each title in the following pages its appropriate Antidotes and Antagonists are given, for every substance which is liable to be used as a poison.
A Compend of Materia Medica, Therapeutics, and Prescription Writing, 1902, by Sam'l O. L. Potter, M.D., M.R.C.P.L.