Yohimbine.—This is an alkaloid which is obtained from the bark of Corynanthe Yohimbi Schum., a rubiaceous tree growing in the Southern Cameroons district in Africa. The bark comes into commerce in flattened or slightly quilled pieces 75 cm. long to 4 to 8 mm. thick, with an external corky layer of a gray-brown color covered with. isolated lichens. It shows numerous longitudinal and transverse fissures like some old specimens of cinchona bark. The transverse fracture is of a uniform yellowish-brown color, and presents short, soft fibers like rough velvet. The taste is bitter.
The alkaloid has been obtained in white needles melting at 234° C. (453.2° F.) and having the composition C23H32N2O6.
The salt of this base that is ordinarily used is the hydrochloride, being preferable on account of its solubility and high percentage of the alkaloid.
It was originally investigated by Oberwarth and Loewy (V. A. P. A., cliii, and B. K. W., No. 42, 1900), who found it to be in animals and also in man a very active excitant to the sexual organs and functions. On the other hand, Kravkoff, as the result of experiments upon the lower animals and upon man, concluded that it has no aphrodisiac effects and frequently produces nausea, salivation, irritability, and other disagreeable results.
Muller (A. I. P. T., 1907, p. 65) found that yohimbine, in small doses stimulated, and in large doses depressed, the respiratory center. If lethal doses are given the heart continues beating after the respiration has ceased. Small doses have little effect upon the blood pressure, but moderate-sized doses caused a slight rise in the blood pressure with local dilatation of the vessels of the pelvic organs. He believes that its aphrodisiac action is due to an increase in the excitability of the lower centers in the spinal cord. On the other hand, many authors believe that its effect is due to the hyperemia produced. Toff (D. M. W., 1904) has found it useful because of this effect in scanty or irregular menstruation.
It has been used by numerous clinicians in neurasthenic impotence, with reports which are generally favorable to its influence. (For literature, see M. R., 1901, 1902.) It is said to be of no value when the impotence depends upon organic nerve trouble, and to be harmful when it is caused by chronic inflammatory disease of the sexual organs or of the prostate gland. Dose, of the hydrochloride, 0.005 Gm. (one-twelfth grain), either in tablet or solution, three or four times a day. Yohimbine has also been employed in a 1 per cent. solution hypodermically.
The Dispensatory of the United States of America, 1918, was edited by Joseph P. Remington, Horatio C. Wood and others.