Action of Poisons

ACTION OF POISONS Poisons may have a local action or a general systemic action after absorption into the circulatory system, or they may act in both ways. Almost all poisons have a general systemic action. Some poisons such as "corrosives" destroy the mucous mem brane or tissues with which they come in contact and cause serious or dangerous injury thereby. Irritant poisons set up a local inflammatory reaction in the mucous membrane of the alimentary tract.

Apart from these local effects, the common result of the absorp tion of a poison is the harmful effect produced by the poison on the important organs of the body, for example, the liver, kidneys, heart and nervous system are almost certain to be adversely affected. A poison after absorption attacks all the organs of the body to a more or less extent and it is a mistake to regard poisons as being exclusively selective in their action though some poisons appear to direct the brunt of their attack on a particular system.

Among the conditions affecting the action of a poison may be mentioned the following : I. The Amount the quantity of a poison taken bears a relation to the effects produced ; exception to this rule are substances in the case of which owing to the quantity taken vomiting occurs so that most of the poison is expelled; oxalic acid and tartar emetic are examples.

The term "fatal dose" when applied to a poison means the smallest amount which is known to have caused death in an adult. Frequently larger doses may be taken without death resulting, but much depends on other factors than quantity, and also as to whether adequate treatment has been adopted.

2. tolerance to some poisons occurs after their repeated use, and in some cases doses far greater than a normal "fatal dose" may be tolerated without serious symptoms develop ing; examples of such drugs are morphine, opium, cocaine and alcohol. In the case of some of these poisons their repeated use leads to the development of the "drug habit" with all its pernicious symptoms and effects.

3. persons are exceedingly intolerant of certain drugs which in moderate doses may cause in them dan gerous or even fatal symptoms; examples are salicylates and aceto-salicylic acid which in some persons have a severe cardio , depressant action.

4. children are much more susceptible to the effects of a poison than adults. The dosage of drugs in the case of children has been fixed by a pharmacological rule, but exceptions to this are morphine, opium and its preparations which are much more toxic than the rule would indicate ; on the other hand chil dren tolerate belladonna preparations better than adults. Aged persons withstand poisons badly.

5. The State of

disease, usually drugs are much more toxic and this is especially so where the excretory organs are diseased. For example, in nephritis medicinal doses of such drugs as morphine, salvarsan, hyoscine, etc., often cause dangerous symptoms, likewise in cirrhosis of the liver there is a greatly increased susceptibility to such drugs. In conditions of gastritis or enteritis irritant drugs like arsenic are especially toxic.

On the other hand in some conditions associated with delirium or pain large doses of sedative drugs produce little effect provided that the excretory organs are healthy.

6. Condition and Mode of

a poison is taken by the mouth in solution it acts much more powerfully than if in an insoluble form, for example, an insoluble prepara tion of arsenic may produce little poisonous effect even in large doses ; similarly strychnine given in hard pills has a much delayed action.

The state of the stomach as regards the presence of food has a marked influence on the effect of a poison ; for example, if the stomach is empty the effect will be rapid, particularly so when the poison is in a soluble form ; on the other hand if the stomach is full considerable delay may occur in the action of the poison as is well shown in acute arsenical poisoning.

Poisons administered subcutaneously or intravenously act more powerfully than by the mouth.

When a poison is inhaled in the form of spray, vapour or gas its absorption from the respiratory tract is rapid and the effect great. Poisons may be absorbed by the skin or mucous membrane of the vagina or rectum with fatal result.