518. Digitalis.
The carefully dried leaves of Digita'lis purpurea Linné, without admixture of more than 2 per cent. of stems, flowers, or other foreign matter.
BOTANICAL CHARACTERISTICS.—Biennial, hoary-pubescent. Leaves alternate, ovate-lanceolate, crenate, rugose. Racemes terminal, loose; flowers purple, sometimes white, hairy, and spotted within.
SOURCE.—The plant is indigenous to Southern and Central Europe, particularly in the western section, and grows wild as far north as Norway, also in Madeira and the Azores, and is cultivated in the United States. It is found on the edges of woody land and prefers sandy soil.
It is claimed by some investigators that Digitalis leaves of the first and second year's growth have proved identical in their activity, and the cultivated leaves are at least as active as those wild grown.
DESCRIPTION OF DRUG.—The margin of this leaf is rather irregularly double crenate. In the market it comes in wrinkled, velvety fragments, the lower surface paler green than the upper, softly pubescent, especially along the midrib and veins; the midrib is prominent, but not so much so as in hyoscyamus; the venation forms prominent meshes on the under surface of the leaf, the principal veins joining the midrib at a very acute angle; odor slight and characteristic; taste strongly bitter.
ADULTERATIONS.—Other dried leaves are sometimes mixed with digitalis, the commonest of these are: Inula conyza (Conyza squarrosa), spikenard, and Inula helenium, both having entire, instead of crenate or serrate, margins, and the latter having its veins branching off at about right angles to the midrib, accidental impurities, such as Comfrey leaves, Symphytum officinale, have been found. These are lanceolate and bear isolated stiff hairs.
Powder.—Characteristic elements: See Part iv, Chap. I, B.
CONSTITUENTS.—The exact chemical composition of digitalis is a vexed question, but the latest analysis shows it to be composed of at least five principles: digitalin, C5H8O2 (soluble in alcohol, insoluble in water), digitalein (soluble in water and alcohol), digitonin, C27H44O13 (readily soluble in water, insoluble in alcohol, the diuretic principle), digitin (inert), and digitoxin, C31H50O10, the most active ingredient, crystalline (insoluble in water, and sparingly soluble in alcohol, deposited as a sediment from the alcoholic preparations of the leaf). Digitoxin, by recent experimentation, is found to yield with hydrochloric acid digitoxigenin, C22H32O4, and a glucose, digitoxose, C9H18O6, the former in colorless crystals.
DIGITALIS PRINCIPLES.—The search for pure principles representing the complete action of the drug seems to be hopeless, but many proprietary preparations have been countenanced, in a measure, by the Council of the A.M.A. These are: Digitalein, Crude; Digitalin, True; Digitalin, "French;" Digitalin, "German;" Digitoxin; Digitoxin-Merck. These principles are all described in "New and Non-official Remedies." Ash not to exceed 15 per cent.
TEST.—If made into a fluidextract and assayed biologically the minimum lethal dose should not be greater than 0.0006 mil of fluidextract, or the equivalent in fluidextract of 0.0000005 Gm. of ouabain, for each gramme of body weight of the frog.
Preparation of Digitalin.—A concentrated fluidextract is first treated with water acidulated with acetic acid and charcoal. The filtrate is neutralized with ammonia, then precipitated with tannin. The washed precipitate is then rubbed with lead oxide, boiled with alcohol, decolorized, and filtered. Evaporate to solid and wash with ether. In this way a digitalin of indefinite composition is obtained, consisting of such glucosides as digitin, digitonin, etc.
ACTION AND USES.—Cardiac tonic and stimulant and diuretic. It slows the heart's action and increases its force, and by stimulating the vascular nervous system causes contraction of the arterioles and therefore greatly increases arterial tension. Its efficient diuretic action in cardiac diseases is due to its peculiar effects upon the general and renal circulations. Dose: 1 to 2 gr. (0.065 to 0.03 Gm.). Dose of digitalin: 1/10 gr. (0.006 Gm.), much depends on the quality. Digitalin, "French." Homolle's Digitalin, for example: Dose: 1/250 to 1/35 gr. (0.00025 to 0.002 Gm.), Digitoxin 1/120 gr. (0.0005 Gm.), Digitalein, crude 1/60 gr. (0.001 Gm.).
- OFFICIAL PREPARATIONS.
- Infusum Digitalis (1.5 per cent.) Dose: 1 to 4 fl. dr. (4 to 15 mils).
- Tinctura Digitalis (10 per cent.), 5 to 30 drops (0.3 to 2 Mils).
- Fluidextractum Digitalis 1 to 2 drops (0.065 to 0.13 mil).
