This section is from the book "Materia Medica Pharmacy, Pharmacology And Therapeutics", by W. Hale White. Also available from Amazon: Materia Medica Pharmacy, Pharmacology And Therapeutics..
This term is often applied to substances which aid the expulsion of gas from the stomach and intestines. They act by stimulating the gastric and intestinal movements. It has been found from clinical observation that the most efficient carminatives are -
(1) Stomachics generally, especially -
(4) Pungent substances,
(8) Camphor and
(9) Volatile oils.
8. Emetics. - It is well known that the many complicated mechanisms involved in the act of vomiting are under the control of a centre in the medulla, which is capable of being stimulated by afferent impulses reaching it from many sources, such as the cerebrum, as when sights or smells cause sickness, the mouth, the pharynx, the oesophagus, the lungs, the heart, the stomach, the intestines, the biliary passages, the kidney, the peritoneum, and the uterus; so that the drugs acting on any of these organs, or on the centre itself, might be emetics. But it is usual, in describing drugs which cause vomiting, to mention only those which do so either by acting on the stomach or on the centre in the medulla, and they are divided into two corresponding classes. Those acting on the stomach are sometimes called direct emetics, because they act directly on the stomach; and those influencing the medulla are called indirect; but some authors reserve the word direct for those acting on the medulla, and speak of those affecting the stomach as indirect. Considering this confusion, it is better to divide emetics into gastric and central. By means of the following experiments we determine to which group any drug belongs:
(1) The emetic is injected directly into the circulation. If very shortly after this vomiting takes place, the drug must have acted on the medulla, to which it has been carried by the circulation; but if some time elapses we conclude it acted on the stomach, and that it was first excreted into this organ before vomiting took place. This experiment may be made still more striking by injecting directly into the carotid, for then the medulla is quickly reached.
(2) If the least quantity of the drug which, when injected into the circulation, will produce vomiting is larger than is necessary when it is introduced directly into the stomach, the inference is that the drug acts primarily on the stomach, and that when it produces vomiting after injection into the circulation it only does so because some of it has been excreted into the stomach.
(3) If the drug will not produce vomiting after injection into the circulation when the stomach is replaced by a bladder, it shows that it acted directly on the stomach; but if vomiting is produced it shows that the drug acted on the medulla, and that the vomiting is caused by the contraction of the abdominal muscles.
(4) If the drug takes a long while to act after its introduction into the stomach, it probably acts centrally; and the reason for the delay is that sufficient time must elapse for the drug to be absorbed.
In spite of these experiments it is difficult to be sure about the action of emetics, for some act in both ways, and some may, in the course of their circulation through the blood, act upon some of the many parts of the body from which the vomiting centre receives afferent impulses.
The following is a list of those emetics which are commonly used. Emetics acting on the stomach:
(1) Yellow mercuric subsulphate.
(3) Ammonium carbonate.
(4) Copper sulphate.
(5) Zinc sulphate.
(6) Sodium chloride.
(8) Warm water.
Of these zinc and copper sulphate act slightly on the medulla.
Emetics acting on the medullary centre:
(2) Tartar emetic.
Of these tartar emetic and ipecacuanha act partly on the stomach. The first three are very powerful emetics, and are much more depressant in their action than the gastric emetics.
Emetics have two uses. Firstly, to remove the contents of the stomach. Thus when that organ is over-full, and there is a feeling of nausea, an emetic by emptying the stomach may relieve. Emetics are largely used to empty the stomach in cases of poisoning, and they may benefit certain cases of sick headache. An emetic occasionally aids the expulsion of a foreign body which has become impacted in the fauces or oesophagus. Secondly, emetics are used to expel the contents of the air-passages, especially in children, for they cannot expectorate well. For this purpose these drugs are given to help children to expel the morbid products in bronchitis, laryngitis, and diphtheria. They also aid the expulsion of foreign bodies that have become impacted in the larynx. In choosing an emetic it will be remembered that although apomorphine, ipecacuanha, and tartar emetic are the most powerful they are the most depressant, and are therefore not suitable in many cases - such, for instance, as poisoning accompanied by severe collapse. When the poison is a powerful gastro-intestinal irritant, if the condition of the mouth and oesophagus will allow of it, it is preferable to wash out the stomach rather than to use an emetic.
Emetics are not permissible for patients suffering from aneurism, hernia, prolapse of uterus or rectum, peritonitis, or a tendency to haemorrhage, because of the straining induced by the vomiting, which should make us cautious in giving them to those who have disease of their vessels or high tension in them, for the straining may lead to haemorrhage.
9. Anti-emetics. - The causes of vomiting are so numerous that the number of drugs which may stop vomiting is very large; therefore, as in the case of emetics, we can only consider those which act either on the stomach or on the centre in the medulla.