This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol1", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
Medicines are employed by the rectum with two distinct objects; one to evacuate the bowels by simply irritating the part, the other to produce their peculiar and characteristic impression either on the rectum itself, or, through absorption or sympathy, upon other parts, or the whole system. These two objects are often incompatible; and it is necessary, therefore, when the latter effect is desired, to administer the medicine in such a manner as not to produce the former. But, in either case, the patient should be directed to resist the immediate impulse to evacuate the bowels; as, even when the cathartic effect is aimed at, time should be allowed for the influence of the medicine to be extended to the higher portions of the large intestines, which might otherwise not be affected, and only the rectum emptied. Medicines may be administered by the rectum either in the liquid or solid form. In the former case, they are called enemata, injections, or clysters; in the latter, suppositories.
In either of the forms mentioned, the dose of the medicine, when given in reference to its peculiar effects, may be about three limes that given by the mouth. But, as the relative susceptibility of the stomach and rectum varies, it would be a safer course, when the medicine is very active, as in the instances of the poisonous alkaloids, to administer at first about the same dose as by the stomach, and increase afterwards if necessary. There is another important consideration in regard to the relative dose by the stomach and rectum. When an individual has become habituated to very large quantities of the more active medicines by the mouth, as opium, for example, it might be very dangerous to triple the quantity, when administering it per anum. Though, undoubtedly, the loss of susceptibility is mainly in the nervous centres, it is very probable that the stomach experiences the loss in a greater degree than other organs, and that, applied to another part, the medicine might be found to exercise a much greater proportionate influence. It would be best, therefore, in such cases, not only not to triple the dose, but not to increase it at all, and at first even to administer the medicine in much smaller quantity by the rectum than the stomach, until the relative susceptibility of the two parts, or the relative facility of absorption from them, shall have been tested by trial.*
The circumstances under which medicines may be administered by the rectum, in reference to their peculiar effects, are the following: 1. when the stomach is unable to retain them, or from any cause they may be thought injurious to that organ; 2. when it is desirable to produce a very rapid or powerful impression on the system, and thus to seek an entrance into it by every avenue; 3. when, from the long continuance of the indication for the use of any medicine, it is advisable to vary the surface of application, in order to avoid wearing out the susceptibility of the stomach, and thus to prolong the period during which the effects of the medicine may be sustained; 4. when the seat of disease is in parts neighbouring to the rectum, and the disease itself is of such a character as to be relieved by impressions made in its vicinity more speedily and effectually than through the system at large, as in painful affections of the urinary and genital organs; and 5. when the indication is to produce the effects of the medicine upon the rectum itself, as in neuralgia or spasm of that bowel, and chronic inflammation and ulceration of its lining membrane. Medicines are also exhibited in this way, in order to weaken or destroy the thread-worm which infests the rectum.
Enemata. When intended to evacuate the bowels, the enema should measure for an adult a pint or somewhat less, for a youth of twelve years about half the quantity, for a child one or two years old two fluidounces, and for an infant at birth one fluidounce. Too great a quantity, if used habitually, may injuriously distend the rectum, and diminish its power of contraction. Upon the subject of cathartic enemata more will be said under the head of cathartics.
When the object is to obtain any characteristic effect from medicines, other than purgation, the bulk should be small, say from one to four fluidounces, and the vehicle very bland, consisting of pure water, or of some mucilaginous or starchy fluid; and, when there is danger of its being rejected, from twenty to forty drops of laudanum, or an equivalent quantity of some other liquid preparation of opium, should be added, in order to control the irritability of the rectum.
* Experiments performed by Mr. W. S. Savory on the lower animals, especially the rabbit, guinea pig, and rat, show that certain medicines injected into the rectum act much more vigorously, in these animals, than when introduced in the same dose into the stomach. This was true especially of strychnia; but the same results, though in less degree, were obtained with other medicines, as cyanide of potassium and hydrocyanic acid. (Lancet, May 9, 1863, p. 516; also Ibid. p. 548.) Mr. Savory, however, states that, in order to obtain these results, the medicine must be exhibited in the liquid form; as in the solid state the substance often remains long in the rectum without effect. (Med. T. and Gaz., June, 1865, p. 586.) These results of Mr. Savory confirm the propriety of the caution given in the text. In relation to powerful medicines, administered in the liquid form, it would be prudent never to commence with them by the rectum in larger dose than by the stomach. (Note to the third edition).
The most convenient instrument for the administration of enemata is on the whole a good metallic syringe, which may vary in capacity, according to the bulk to be thrown up, from a pint to two fluidounces. The old-fashioned pipe and bladder may be resorted to, in the absence of this instrument. The gum-elastic bottle with a tube is still more convenient. Another instrument, sometimes used in France, is a slender, water-proof, tube-like bag, three or four feet long, two or three inches in diameter at the larger end, and gradually diminishing to the smaller, to which an ivory pipe is attached for insertion into the rectum. When employed, the pipe is introduced, the larger extremity of the bag held up as high as it will extend, and the liquid poured in. This either enters the rectum by its own specific gravity, or may be gently forced in by running the lingers, pressing the bag between them, from the upper gradually down towards the lower end. The self-injecting apparatus, which is a kind of forcing-pump, is very useful when an individual wishes to administer an enema to himself, and also when the object is to throw an indefinite quantity of liquid into the bowels, with the view of overcoming obstruction.* Whatever instrument is employed, the liquid injected, as well as the instrument itself, should be at about the temperature of the interior of the body; and, after the injection, the operator, in cases where there is any disposition to a premature discharge of the liquid, should aid the efforts of the patient to retain it by pressing a warm folded towel against the fundament, until the first irritant effect shall have passed away. Great care should be taken not to wound the mucous membrane by entangling the end of the pipe in its folds, or pressing it against the membrane too strongly. Severe pain is some-times produced by a neglect of this caution. In relation to the medicine injected, if a soluble substance, it should be dissolved; if a solid, or liquid not soluble in water, it should be thoroughly and equably incorporated with the liquid vehicle by means of some suspending substance. When an irritating substance, such as oil of turpentine, is injected, the yolk of eggs is an excellent intermedium.
* The apparatus of Dr. Mattson is very convenient for the same purpose, being exceedingly simple, and easy of application. It consists of a gum-elastic bag. communicating near its orifice with a rectum tube, and having a short tube with a valve opening inward inserted into its orifice, through which the liquid to he injected enters the instrument. The open end of this tube is introduced into the liquid, which is drawn into the instrument, and then forced into the rectum. by the alternate expansion and compression of the bag. (See Boston Med. and Surg. Jaurn., liii. 274).
A still more convenient instrument, which is a modification of Dr. Mattson's, is described in the London Lancet (March 31, 1866, p. 349). It consists of a stout oval gum-elastic bag, communicating at one end with a rectum tube, and at the other with a water-proof bag containing the liquid to be injected, a valve opening inward being placed at the orifice connected with the receiver. By alternate pressure with the hand, it is obvious that the gum-elastic bag will be alternately emptied into the rectum and filled from the receiver until any desirable quantity of liquid is made to enter the bowel. (Note to the third edition).
Advantage might sometimes ensue, in cases in which a speedy operation of the medicine is essential, and the stomach will not retain it, from introducing it by means of a long flexible tube far up into the colon. Being thus diffused over a greater extent of surface, it might possibly be absorbed more rapidly, and in greater amount, and consequently produce a more speedy and powerful effect.
Suppositories. Like enemata, these may be used simply to evacuate the bowels by irritating the rectum, or to produce the peculiar effect of the medicine employed. For the former purpose, they may be of a cylindrical, oval or conical form, an inch or two in length by about half an inch in diameter, and made of some softish material, like soap or cacao butter. For the latter, they should be as small as is consistent with due effect, and preferably of the pilular form; the object being that they should irritate as little as possible. Opium is not unfrequently employed in this way. Suppositories, with a view to systemic effect, have recently come into more extended use. They have even been adopted as officinal in the British Pharmacopoeia. For a fuller account of thisef preparations, see the U. S. Dispensatory (12th ed., p. 1361).
Gaseous Injection. Aeriform substances have sometimes been injected into the rectum, though this method of medication is rare. Atmospheric air thrown up largely has been found useful in overcoming obstruction of the bowels; tobacco smoke has been employed to produce relaxation: and carbonic acid gas has been recommended in certain morbid states of the rectum.
Electric action may also be developed in the rectum, either by introducing a complete metallic galvanic arrangement in a compact form, or by passing a wire connected with one pole into the bowel, and applying the other at some point on the back or abdomen.