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.
In this mode of employing medicines, the epidermis is first removed, and the medicine then applied to the denuded surface. It is by far the most efficient external method. Medicines are rapidly absorbed; and produce their effects in some instances as quickly as when taken by the mouth, or even more so. In cases of great irritability or phlogosis of the stomach, and when the patient cannot or will not take medicines by the mouth, it is an invaluable resource. Other indications for its use are afforded by insusceptibility of the stomach, arising from a long-continued or excessive employment or the medicine, by the necessity in urgent cases of introducing medicines by every practicable avenue, and by the existence of serious local affections, which have refused to yield to remedies addressed to the constitution. The last indication is often very agreeably fulfilled by endermic medication. I have known, for example, vomiting which had resisted all other means, yield to a salt of morphia sprinkled upon a blistered surface in the epigastrium. This method of medication had long been partially employed, as exemplified in the frequent application of mercurial ointment to blistered surfaces; but it was first systematized by Dr. A. Lembert, of France, whose experiments were repeated and extended by Dr. Gerhard, of Philadelphia, by whose essay on the subject the attention of the profession in this country was first extensively called to it. as a useful mode of employing a great number of medicines. (N. Am. Med. and Surg. Journ., ix. 392, A.D. 1830.) Almost all medicines, the dose of which is not very large, or which do not irritate severely, or corrode the surface to which they are applied, may be employed in this way; but it is especially appropriate to the organic alkalies, and to the other more active proximate vegetable principles. Perhaps no medicine acts more efficiently by the endermic plan than the salts of morphia.
The dose of medicines administered in this way may be twice or thrice that given by the mouth. There is less danger here from an over-dose; as what remains of the offending material may be readily removed, should serious consequences be threatened. Sometimes the medicine will be found to act as efficiently as by the stomach in the same dose.
The part best adapted for the application of the medicine, when some local affection does not call for a special direction, is the epigastrium; bat any portion of the anterior surface of the body, or the inner surface of the thighs and arms will answer well. A denuded surface for the purpose is most conveniently obtained by means of a blister of cantharides; though, in cases of great urgency, the more rapid action of the stronger solution of ammonia may be resorted to. Upon the average, the blistered surface may be about three or four inches square. It is not necessary to detach the cuticle immediately. The medicine may be first applied over the raised epidermis, which, if cut freely, will come off with the first dressing.
The medicine should be reduced to the state of a very fine powder, and, if irritant, should be diluted with pulverized gum arabic, or other bland substance, and then sprinkled equably over the surface, or applied upon dressings of simple cerate. If so soft that it cannot be powdered, it may be rubbed up with solution of gelatin, glycerin, mucilage, lard, or cerate, and applied upon pledgets of lint; and substances originally liquid may be applied in the same way.
Care should be taken to avoid irritation as far as possible. Active congestion and inflammation, independently of the pain and inconvenience, interfere with the operation of the medicine by offering an impediment to absorption. Sometimes sloughing results from the incautious use of an irritant medicine, and a permanent scar is left. I have known this to follow the application of sulphate of quinia undiluted.
In cases of excessive constitutional action from the medicine, it may sometimes be advantageously followed, after removal, by a counter-agent. Thus, unpleasant symptoms from strychnia or digitalis, might possibly be relieved by morphia applied to the blistered surface; and the effects of morphia are said to have been neutralized by musk.