Guaco.—This name is given in Central and South America and the West Indies to various plants belonging to the genera Willoughboea (better known under the newer name, Mikania. and Aristolochia;but it is in its application to the different species of the former genus that the drug is known in medicine. The species most used is W. amara (Willd.) O. Kze. (Mikania amara Willd.., and M. Guaco, genus Eupatorium, Humb. and Bonpl. Plants closely allied to the M. Houstonis (Willd.) O. Kze. —as M. gonoclada (DC.) O. Kze. (of the Fam. Composites); Aristolochia fragrantissima Ruiz., A. grandiflora Sw., A. pentandra Jacq. (of the Fam. Aristolochiaceae); Comocladia integrifolia Jacq. (Fam. Anacardiaceae)—are also known locally as guaco. M. amara is described as having twining stems, with round, sulcate, and hairy branches; ovate subactt-minate, remotely dentate leaves, somewhat narrowed at the base, rough above and hairy beneath, and flowers in opposite axillary corymbs. The plant is a native of tropical America, and has been introduced into the West Indian Islands from the continent. The leaves are the part used. The result of a long and close investigation into the natural history of guaco by Guibourt is, that the guaco from this source, instead of possessing, as has been asserted, a strong, penetrating, and nauseous odor, is in fact inodorous, and destitute of all active properties, and that the strongly aromatic plants which have been employed under the name of guaco all belong to the genus Aristolochia, especially A. cymbifera Mart. and Zucc., growing in Brazil, after this A. maxima (DC.), and in less degree A. maxima Jacq. (A. geminiflora H.B.K.). (J. P. C., 1867, 99.)
Although the guacos of South America seem to be entirely distinct drugs they appear to be indiscriminately used by the natives for the cure of the bites of poisonous serpents. The medicine is also used in South America as a febrifuge and anthelmintic, and has been considered antisyphilitic. A few years ago it attracted on the continent of Europe considerable attention on account of its alleged power in epidemic cholera and chronic diarrhea. The Aristolochia cymbifera Mart. and Zucc. has been the subject of a careful study by L. Butte. (Annales de la Policlin. de Paris, Sept., 1890.) The root of this plant as it occurs in commerce is cylindrical, from three to four centimeters in diameter, much broken up into long rootlets, yellowish, with a strong odor, especially in the bark. The plant itself is a vine, growing in great abundance in the province of Tabasco in Mexico. Butte was not able to find in it either an alkaloid or a glucoside, but he found a blackish resin which may be the active principle of the plant, though this does not seem probable, since Butte found the alcohol extract much less active than the aqueous extract, which would hardly be the case if the resin were really the active principle. In the physiological experiments made with the aqueous extract it was found that massive doses produced cries and excitement, followed after a time by sleep, with muscular relaxation and symptoms of gastro-intestinal irritation. There was also depression of the nerve center, both sensory and motor. If the dose were sufficient death was produced by an arrest of the respiration. The heart continued to heat after the cessation of respiration; nevertheless there was depression of the arterial pressure, apparently due to the action of the drug upon the heart. After death marked signs of irritation of the gastro-intestinal tract and kidneys were found. Butte believes that guaco has valuable therapeutic properties in the treatment of skin affections, especially eczema and pruriginous maladies, in which he used it both locally and internally. He gives the dose of the aqueous extract of guaco as three grains (0.2 Gm.) three times a day. In the external' application the following formula was used. Guaco (bruised), 30 parts; sodium bicarbonate, 5 parts; water, 1000 parts; boil for a quarter of an hour, allow to macerate one hour, decant, and use the liquid as a lotion. Guaco is said to be largely used in South America as an antirheumatic and E. W. Pritchard (P. J., 1861) affirms that in the gouty paroxysms it is especially effective given in the dose of a fluidrachm (3.75 mils) of the tincture every four hours, and applied locally.
The Dispensatory of the United States of America, 1918, was edited by Joseph P. Remington, Horatio C. Wood and others.