Source. Digitalis consists of the leaves, collected from plants of the second year's growth, of Digitalis purpurea, the Purple Foxglove, a plant of the nat. ord. Scrophularineae, which grows wild in Europe, and is cultivated in this country, often in private gardens, for its beautiful spike of purple flowers, and largely by the Shakers for the drug market.
Much of the leaf found in our shops is of very poor quality, a large proportion being inert; but whether this is due to our Phar. not restricting the official drug to the wild plant, or to careless treatment in gathering and drying, is not definitely known. When, however, the leaves are imperfectly dried, a process of decomposition sets in which destroys the active principles, and may produce new and poisonous ones. A similar decomposition is said to occur whenever the tincture of Digitalis is mixed with watery or syrupy solutions. Certain it is, at any rate, that Digitalis is one of the most unreliable drugs, in respect of the physiological activity of any particular sample or preparation. The seeds are known to contain the active principle in much greater proportion than the leaves, but they are never used.
Composition. Schmiedeberg's latest analysis is now accepted as the most accurate determination yet obtained of this vexed question. He enumerates five principles, at least, as contained in Digitalis, viz.:—(1) Digitalin, amorphous, insoluble in water, but readily soluble in alcohol; the active ingredient of Homolle's French Digitaline and the Digitalin of the U. S. and Br. Pharmacopoeias ;—(2) Digitoxin, insoluble in water and sparingly soluble in alcohol; the most active of all, and the principal constituent of Nativelle's prize Digitaline ;—(3) Digitaleïn, soluble in both water and alcohol ;—(4) Digitonin, readily soluble in water, sparingly so in alcohol ;—active, but acts like Saponin, forming a solution which froths easily and antagonizes the other three —(5) Digitin, which seems to be entirely inert. The first three are cardiac poisons, the fourth antagonizes them; all five are non-nitrogenous, and except Digitin, are glucosides. Digitalis contains no alkaloid.
Preparations, vary greatly in results, by reason of the different solubilities and actions of the active principles:—
- Digitalis, Folia Digitalis, Digitalis Leaves,—Dose, gr. ss-iij.
- Extractum Digitalis, Extract of Digitalis,—Al. 2, Aq. 1. Dose, gr. ⅙-j.
- Extr. Digitalis Fluidum, Fl. Ext. of Digitalis,—Al. 3, Aq. 1. Dose, ♏j-iij.
- Tinctura Digitalis, Tincture of Digitalis,—15 per cent. Dose, ♏v-xxx.
- Infusum Digitalis, Infusion of Digitalis,—11/2 per cent., with 71/2 of Alcohol, and Cinnamon Water 15. Dose, ʒj-iv. Notice that the dose is in drachms, not ounces.
- *Digitalinum, Digitalin,—the complex product of the process formerly official in the U. S. Pharmacopoeia. Dose, gr. 1/60-1/30.
Note on the Preparations.—Of the above, the Tincture and Fluid Extract, being alcoholic preparations, contain a large proportion of Digitalin and Digitaleïn, with a small proportion of Digitonin; the Digitoxin going to the bottom as an insoluble precipitate. The Infusion contains a larger proportion of Digitonin than of the others, some Digitaleïn, and little or no Digitoxin or Digitalin. It is best for diuretic action, the Tincture for acting upon the heart; but to obtain the action of the plant itself, the powdered leaves must be used in pill or capsule.
Physiological Action. Digitalis is a cardiac tonic and a vascular stimulant, also a motor-excitant, paralyzant, anaphrodisiac, diuretic and an emetic. In overdoses it irritates the mucous membranes, causing sneezing, severe gastric disturbance, nausea, vomiting, colic and purging, the discharges being of a grass-green color. It lowers temperature, probably by lessening the blood-supply to the tissues, produces headache, irregularity of the heart's action. vertigo and an appearance of vibratory fringes of color around objects.
The Heart is slowed by Digitalis, but its force is at the same time increased. The drug stimulates the cardiac motor ganglia, the inhibitory apparatus, and the vaso- motor centre, contracting the arterioles, and thereby greatly raising the arterial tension. Full doses continued exhaust the irritability of the motor ganglia and paralyze the cardiac muscle itself. The recumbent posture must be maintained when Digitalis is given for its full cardiac effects. Its general effect on striped muscular tissue is to lessen the contractile power, causing great weakness and languor. Under it, the excretion of urea is at first increased, but soon decidedly diminished. It lessens the sexual appetite and impairs the venereal function.
The Diuretic Action of Digitalis is due to its peculiar influence upon the general and renal circulation, it increasing the force of the ventricular contractions, while at the same time one of its constituents, Digitalin, contracts the blood vessels of the body, the two others, Digitoxin and Digitaleïn, dilate the renal arteries. The effect of this combined action is to greatly raise the arterial tension and the blood-pressure in the glomeruli, their efferent vessels being contracted ;—while the rapidity of the renal circulation is increased and its volume augmented, by the greater force of the heart-beat and the dilatation of the afferent vessels. No other drug known has this double power, and therefore, so far as vascular action is concerned, Digitalis is the ideal diuretic. Still, while its power to produce diuresis in cardiac disease is unquestioned, most observers deny that it has any such power in health.
Lethal Doses lessen the reflexes by stimulation of Setschenow's centre, and paralyze the muscles and the peripheral nerves, motor and sensory. Respiration, at first slowed, becomes rapid and feeble; cyanosis, coma and convulsions follow, and death by sudden paralysis of the heart, which is arrested in systole.
Aconite compared with Digitalis. Aconite at first stimulates but soon relaxes inhibition, and depresses the cardiac motor ganglia ;—Digitalis increases inhibition, and stimulates the cardiac muscle. Both drugs finally paralyze the heart—Aconite by direct depression, Digitalis by over-stimulation. Under Aconite, the heart is arrested in diastole,—under Digitalis, in systole. The arterial tension is lowered by Aconite,—raised by Digitalis. Aconite acts quickly,—Digitalis very slowly; a fact which makes the latter drug of little value in poisoning by the former. Both drugs slow the heart, but otherwise antagonize each other in their cardiac actions.
Antidotes and Antagonists. The chemical antidote is Tannic Acid, but as the tannate is not inert, the stomach should be evacuated. Aconite is the best antagonist to the effects of large doses, Opium to those of its long-continued use. Saponin and Senegin are considered to be its most complete physiological antagonists.
Therapeutics. Digital is said by Phillips to be particularly adapted to blondes, and persons of sanguine and indolent temperament. Its chief uses in disease are based on its properties as a heart tonic and a diuretic. In—
- Mitral Disease, when the heart is rapid and feeble ;—it moderates hyperaemia of the lungs, and engorgement of the pulmonary veins, by giving the auricle time to empty itself through the obstructed orifice.
- Aortic Disease,—Digitalis gives relief when the cardiac muscle fails, and compensatory hypertrophy has not set in. Otherwise it will not.
- Irritable Heart of soldiers,—Da Costa finds it often curative.
- Dilated Right Heart,—Digitalis gives miraculous relief.
- Palpitation, Cardiac Failure, Venous Engorgement, are all well treated by the Tincture of Digitalis, in medium doses, given on bread pill or sugar.
- Simple Hypertrophy, Pericarditis, Fatty Heart,—are conditions in which Digitalis must not be used, except temporarily for special reasons.
- Dropsy, both cardiac and renal,—Digitalis is well indicated. The infusion is regarded as the best diuretic, while alcoholic preparations, (tincture, fluid extract), are employed to act on the heart.
- Pneumonia, and other inflammations, in first stage,—it is useful. Scarlet Fever, in the early stage, and when the kidneys strike work—Digitalis, in small doses, is an admirable remedy.
- Hemorrhage from a large surface, and in the hemorrhagic diathesis.
- Congestive Headache, Hemicrania, etc., —it raises the vascular tone.
- Mania, Delirium Tremens, and other congestive mental conditions.
- Exophthalmic Goitre,—Digitalis is an excellent remedy.
- Fevers,—in Germany this drug has been much used as an antipyretic, especially by Liebermeister, who, however, has lately advised against it.
Cumulative Action of Digitalis. During a course of this drug sudden alarming symptoms may arise, due to exhaustion of the cardiac motor ganglia. They may be prevented by strictly maintaining the recumbent posture, and stopping the remedy for a few days in every two weeks. This cumulative action has been denied lately by many authorities.
A Compend of Materia Medica, Therapeutics, and Prescription Writing, 1902, by Sam'l O. L. Potter, M.D., M.R.C.P.L.