Pyrogallic acid. A triatomic phenol.

Properties

Gallic acid, subjected to a high temperature, loses its water of crystallization and becomes pyrogallic acid. This is a white, shining powder, crystalline in structure, without odor, and having a persistent bitter taste. It is soluble in two and a half parts of water, and to some extent in alcohol and ether. For exhibition by the stomach, the pill-form is best, the excipient being some unoxidizable substance, and the coating complete. The dose for internal administration will range from one sixth of a grain to two grains. For topical application, solutions are preferred, and they vary in strength from one to ten per cent. Solutions can not be kept long, because of chemical changes; exposed to light, the color becomes brownish, and the power declines with the loss of oxygen.

Pyrogallic acid is an active poison, and this property is exhibited as well when administered by the stomach as when applied to an abraded surface on the skin. Caution in its use becomes necessary, therefore, for several instances of fatal poisoning, and numerous cases in which the toxic action was stopped by treatment, have been reported..

Pyrogallic acid is an irritant poison, and all the characteristic actions of that group of remedies follow its administration in sufficient quantity—nausea, vomiting, purging, accompanied by intense gastroenteric inflammation (Besnier). The changes wrought in the blood are significant in a high degree. It impairs or destroys the respiratory function of the blood by the damage it inflicts on the red corpuscles, which are disorganized, the haemoglobin separated. Changes in the intima of the blood-vessels, fatty and fibroid degeneration of organs, especially of the liver and kidneys, are constant results of its toxic activity (Neisser); and of these lesions, we find the clearest evidence in the changes which take place in the urine, which becomes brown, almost black, and by the presence in it of haemoglobin, or the products of its decomposition. Decline in temperature, profound anaemia, haemorrhages, especially haematuria, are also most clearly significant of the toxic action. It need hardly be observed that such dire results are toxic, and the quantity of the agent necessary to produce them is much beyond ordinary medicinal doses.

The elimination of pyrogallic acid takes place by the ordinary channels, but especially by the kidneys and liver. It is probable that the structural changes in the eliminating organs are due to the immediate contact of the acid as it passes out of the system.

Therapy

The use to which pyrogallic acid was first applied, was suggested by its therapeutical relationship to chrysarobin. As is now well known, chrysarobin, under the designation "Goa-powder," has proved to be an efficient remedy for psoriasis and parasitic affections of the skin. If pyrogallic acid is not so certain, which may well be doubted, it has great advantages. Both color and irritate or inflame the skin, but pyrogallic acid is far less injurious in its local action (Jarisch).

Having very powerful germicide action, pyrogallic acid is an efficient remedy in pityriasis versicolor, herpes tonsurans, favus, etc., and it has also exhibited some curative action in more serious affections, as lupus and epithelioma.

The strength of the solutions used has ranged from one hundredth to one tenth per cent. The ointment made in these proportions with vaseline or lard—more frequently vaseline—is held to be less effective than solutions of the same, which are also more readily applied (Arra-gon, Kaposi).

If the solutions or unguents are too strong, or frictions too forcibly made, violent inflammation may be set up, and permanent injury done to the skin. More or less brownish discoloration of the skin is an effect of the application, but it is not permanent. The aqueous or alcoholic solution of pyrogallic acid can be applied to the affected surface by means of absorbent cotton, the strength of the solution and the duration of the application being regulated by the effect it has on the diseased surface. As, however, toxic effects follow if the application is made over too extensive surface, a part of the diseased area only should be treated at one time.

M. Vidal has made the important announcement that the ointment of pyrogallic acid is an excellent application to chancroid, especially if it tends to slough. A few applications change the character of the sore, and soon effect cicatrization.

In the treatment of ulcers, sloughing phagedena, epithelioma, and similar conditions, pyrogallic acid may be mixed with a powder—kaolin or starch, for example—and then well dusted over the diseased part.

Authorities referred to:

Besnier, Dr. E. Bul. Gén. de Thérap. for 1884.

Hamilton, Robert, F. R. C. S. On the Employment of Tannic Acid in some Diseases of the Eye and Eyelids. The Practitioner, vol. ii, p. 347.

Hanbury and Fluckiger. Pharmacographia, pp. 170, 213, 536, et seq.

Husemann, Drs. August und Theodor. Die Pflanzenstoffe, 996, and pp. 1002,1006, 1008, et seq.

Jarisch, Dr. A. Centralblatt für die gesammte Therapie, vol. i, p. 17, et seq.

Kaposi, Prof. Dr. Ibid.

Neisser, Dr. Annuaire de Thérap., 1883.

Porcher, Dr. Francis Peyre. Resources of the Southern Fields and Forests: Various articles on the indigenous remedies mentioned at the head of this article.

Ringer, Dr. Sidney. On the Glycerine of Tannin. The Practitioner, vol. i, p. 27. Ibid., Handbook of Therapeutics.

Waldenburg, Prof. Dr. L. Die locale Behandlung der Krankheiten der Athmungs-organe, Berlin, 1872, p. 237, et seq.

Waldenburg und Simon. Handbuch der Arzneiverordnungslehre.