A family of alkaloids, originally prepared from extracts of Digitalis purpurea, the foxglove plant, which are one of the most ancient herbal medications to have a definite pharmacologic effeect. A mixture of alkaloids in the plant improve the pumping ability of the heart (i.e., show positive inotropic effects).
The therapeutic index of these alkaloids, or the ratio between the effective and toxic dose, is narrow. Since the mixture and concentration of the alkaloids, in a given plant and by traditional extraction methods, varies widely, the version used in conventional medicine is made synthetically so that its activity is predictable. The most commonly used alkaloid, digoxin, also has a half-life that is convenient for once-daily dosing.