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.
(9) _To relieve chronic constipation._ In selecting a cathartic for this
purpose we will be guided so far as possible by local conditions. The
trouble may be in the small intestine, colon, or rectum. We must decide
whether it is due to diminished peristalsis, or secretion, or too rapid
absorption. If it is due to a relaxed condition of the muscles of
descending colon and rectum, aloes is efficient. If it is due to general
relaxation of the intestinal muscles, physostigmine or strychnine may be
of use. If there is a diminished secretion or increased absorption the
ingestion of more water and foods containing water, as fruits and
vegetables, will sometimes be of service.
(10) _To purge the nursing child._