Cathartics are not only of use to remove feces, but owing to the physiological relation of the intestinal tract to the other organs, they are often of great service in a number of different pathological conditions. With a knowledge of their mode of action we can select on a rational basis the proper cathartic for the different indications.
Cathartics are indicated:
(1) To remove dropsical effusions. In disease of the liver, heart, kidneys, etc., there are sometimes accumulations of serum in the serous cavities and subcutaneous cellular tissue. For this purpose those which stimulate secretion and cause a profuse watery discharge are best suited. When the effusion is due to obstruction in the liver so that the serum leaks from the congested postal vessels, they are most prompt in action, because they drain the water from the postal vessels and lower the high portal pressure. Magnesium sulphate, elaterium, and gamboge are efficient here.
(2) To remove urea, etc., from the blood. Sometimes the kidneys are so diseased that they cannot excrete the waste matter from the body, and its action, when abnormally accumulated, causes serious symptoms. For this purpose use those which cause watery stools, so as to wash the waste out through this channel. If the case is urgent as in uremic convulsions or coma, croton oil is the best to use, because it can be dropped on the tongue and does not have to be swallowed, and, besides, acts in an hour or two. As it is a violent irritant, it should not be continued.
(3) To lower high systemic pressure. High arterial tension often increases the disease as sometimes occurs in cerebral hemorrhage, in meningitis, and at the beginning of many acute diseases. Those drugs are of use which cause great dilatation of the intestinal vessels, draining the blood from the other organs, or which cause a profuse watery discharge from the blood. In this way croton oil is of use in cerebral hemorrhage, calomel in meningitis, etc.
(4) To depress the liver when it is excessively active. In that condition known as “biliousness,” where there is congestion of the liver, and enormous quantities of bile are poured into the intestine, chologogue cathartics are needed, because they remove all this bile from the duodenum, and give the over-active liver rest.
(5) To deplete the mucous membrane in gastro-duodenitis. When persons of a certain predisposition over-eat there is congestion or even inflammation of the gastro-intestinal mucous membrane. This extends up the bile-duct, and the swelling occludes it, so that the outflow of bile is obstructed, and soon it diffuses into the blood, and the person becomes jaundiced. The salines, specially sodium salts, are here of use, because they drain away the water without stimulating the mucous membrane, and hence lessen the hyperemia.
(6) To stimulate the torpid liver. This is not in biliousness, but when the liver does not secrete bile enough; the patient is constipated, and the stools are too light from lack of bile.
(7) To remove pathogenetic material from the bowels. Diarrhea is usually caused by the irritation of toxines formed by the growth of bacteria in the intestinal liquids. In the adult when this is an acute attack, salines are best to wash them out. In the child, when this continues for days, it is better to select those cathartics which are bactericides, so as to kill them, such as calomel and gray powder.
(8) To remove feces. This is probably the most common use of cathartics. Those which slightly increase peristalsis and secretion are adapted for this. The drastic purgatives are too strong for this purpose. Among those commonly used are magnesia, sulphur, castor oil, rhubarb, senna, cascara sagrada, jalap, podophyllin, and salines.