This section is from the book "Materia Medica And Therapeutics: An Introduction to the National Treatment of Disease", by John Mitchell Bruce. Also available from Amazon: The pharmacology and therapeutics of the materia medica.
Digitalis Folia-Digitalis Leaves.-The dried leaves of Digitalis purpurea. Purple Foxglove. Collected from wild indigenous plants, when about two-thirds of the flowers are expanded.
Characters.-Ovate lanceolate, shortly petiolate, rugose, downy, paler on the under-surface, crenate.
Substance resembling Digitalis Leaves: Matico, which is more deeply reticulated.
Composition.-The active principle of digitalis, known as digitalinum, or digitalin, occurs in two forms: (a) Homolle and Quevenne's digitalin, a yellowish-white amorphous, or scaly very intensely bitter substance; and (b) Nativelle's digitalin, in crystalline prisms, also very bitter. It is now known to be a compound of four bodies, namely, (1) Digitalin proper, insoluble in water, forming the bulk of Homolle's digitalin; (2) Digitalein, very soluble in water; (3) Digitoxin, insoluble in water, and the chief constituent of Nativelle's digitalin; and (4) Digitonin, probably the same as saponin, the active principle of senega. Digitalein seems to possess the properties of a mixture of digitalin and digitonin. Digitoxin is by far (7 times) the most powerful, a local irritant, and a muscular depressant; and therefore, and because insoluble, unfit for use. None of the constituents are so suitable as digitalis leaf itself.
1. Digitalinum. Digitalin. - A complex active substance obtained from digitalis. Source.-Made from (1) an alcoholic extract, by dissolving out the Digitalin with Acetic Acid and Water; (2) decolorising with Charcoal ; (3) precipitating the impure Digitalin with Ammonia and Tannic Acid; (4) removing excess of Tannic Acid by Oxide of Lead; (5) dissolving in Spirit; and (6) purifying with Charcoal and Ether. Characters.-Porous mamillated masses, or small scales, white, inodorous, and intensely bitter. Dose, 1/60 to
Infusum Digitalis. 1 in 160. Dose, 2 to 4 fl.dr.
3. Tinctura Digitalis,-1 in 8. Dose, 5 to 30 min.
Internally, in full doses, it deranges the stomach and bowels; dyspepsia, vomiting, and occasionally diarrhoea following its continued use in small doses-effects which are partly local, partly specific, and to be carefully avoided or checked in practice.
The active principles of digitalis enter the blood freely. Thence they reach the tissues more quickly than they leave them; and doses, however small, if closely repeated, tend to accumulate in the body. The action of digitalis is mainly confined to the circulatory organs, the other parts being chiefly affected secondarily. Both the heart and vessels are influenced by the drug, the action of which occupies four stages, the first stage being shortened and the other stages more marked as the dose is increased. In the first stage, the heart falls in frequency (say to fifty per minute), from stimulation of the vagus in the heart and medulla ; and beats with increased force, from stimulation of the intrinsic ganglia. Therewith the arterial pressure rises, from the increased cardiac force, and from excitation both of the vaso-motor centre and vaso-motor nerves. The result of all this is that the ventricles are well filled (diminished frequency, i.e. lengthened diastole); the ventricles are thoroughly emptied (increased force); the arteries are thus well filled ; and they are kept filled (vaso-motor action.) The condition is that of a perfect circulation, which empties the veins and fills the arteries.
In the second stage, the state of the heart remains unchanged, but the vaso-motor apparatus of the renal arteries are rather suddenly depressed; these vessels are relaxed; and the force of the circulation is thus thrown upon them, that is on the glomeruli. The result is increase in the excretion of urinary water.
In the third stage, the heart rises in frequency, from depression of the vagus, and probably some irritation of the sympathetic (accelerator) fibres; and loses force, from commencing exhaustion of the intrinsic ganglia and muscle. At the same time the arterial pressure falls, from the weakening of the heart, and from depression of the vaso-motor apparatus, which spreads from the kidney, where it commenced, to the other peripheral arterioles. Thus the circulation begins to fail.
In the fourth_stage, the action of the heart becomes irregular, infrequent, ana weak, from failure of the ganglia and myocardium; and is finally arrested in diastole. Therewith the blood pressure gradually sinks to zero, from loss of cardiac force and complete paralysis of the vessel walls. Death occurs by general circulatory failure.
Respiration fails at last, but only through the circulation. The voluntary muscles are paralysed through failure of their blood supply. The uterus is said to be stimulated by moderate doses. The body temperature is briefly raised through increased vigour of the circulation; it is then lowered by the increased blood-flow in the skin; and falls still more in the last stages, in an irregular uncertain way, from causes still obscure. Digitalis is thus a refrigerant. The central nervous system is only secondarily affected through the blood supply. Headache, giddiness, disturbance of sight and vision are frequently induced by medicinal doses of digitalis; with a sense of faintness, depression, nausea, or actual sickness. Metabolism is variously influenced by digitalis, according to the length of the different stages and the rapidity of their development. When the pressure and temperature are high, the urea and uric acid may be increased, and certain salts may be diminished in amount.
The effect of digitalis on the urine is equally uncertain in the healthy individual; the period at which the renal vessels begin to be relaxed, the duration of the second stage, and the relation of the action of the drug on the heart to its action on the vessels, being all variable. As a rule, the urine is not increased in bulk in health, but is remarkably increased in some cases of dropsy to be presently referred to.
Digitalis is one of the most valuable of medicinal remedies, and is employed in the following conditions:
1. Digitalis is indicated in disease of the heart, when the nervo-muscular structures of the cardiac walls fail, so that the circulatory force falls, the cavities are incompletely emptied, the arteries are insufficiently filled, the veins imperfectly drained, and the blood accumulates behind the seat of disease. Such a condition is characterised by cardiac distress and pain; a small, weak, and often irregular pulse; distension of the veins, haemorrhage, dropsy, and visceral disorder; and often by congestion of the lungs, and great dyspnoea. It occurs under a variety of circumstances which demand separate consideration.
The disturbances of the circulation produced by disease of the valves of the heart are removed by a natural process of compensation, consisting of hypertrophy of the muscular walls, with or without dilatation of the cavities. If this compensation do not occur, or fail after having been established, and the circulation be disordered as described, digitalis may give relief, by increasing the force of the cardiac wall; by lengthening diastole, so that the venous flow and the ventricular rest are both prolonged; and by sustaining the pressure on the arteries, thus driving the blood in a steady stream into the veins. All the symptoms will be thus removed, including dropsy, the fluid being absorbed by the increased venous flow, and excreted by the kidneys as a profuse diuresis. Mitral disease, tricuspid incompetence, and aortic obstruction are the forms of valvular disease in which imperfect or failing hypertrophy is relieved by digitalis. In aortic incompetence some authorities forbid the use of the drug, as prolonging diastole, and thus permitting greater reflux, but this practice is not to be carried too far, and digitalis must be given if the ventricle fail. In mild cases, when little more than a tonic effect on the heart is desired, the tincture is prescribed. When dropsy is present, and the patient confined to bed, the infusion or the powdered leaf should be given, and the effect carefully watched. Without nourishing, digestible, and digested food, digitalis can only exhaust the heart, and attention must therefore be paid to the stomach, liver, and bowels. Iron may be combined with advantage, but only after the excretory and digestive functions have been restored. Let it be carefully observed that digitalis is not to be given in a routine fashion for valvular disease, but with reference to the state of the muscular wall associated with the lesion. Digitalis is of great service in failure of the heart from primary disease of the walls, as in chronic myocarditis; in the granular degeneration of acute myocarditis, pericarditis, and endocarditis, occurring in scarlet fever and acute rheumatism; and in acute alcoholism. In fatty degeneration digitalis may have to be withheld, lest irregular contraction and rupture occur. Digitalis restores the vigour of the heart in failing hypertrophy of chronic Bright's disease, when it is breaking down against excessive peripheral resistance; until the heart begins to fail, the drug is contra-indicated, but when dilatation begins it must be given. In functional or nervous palpitation, pain, or irregularity, with debility and dyspepsia, digitalis is often valuable; as also in reflex cases, with gastric disorder, where small doses control the vagus, but must be given intermittently, the dyspeptic effect of the drug also being remembered. Digitalis is harmful in pure hypertrophy. In disease of the right ventricle from chronic lung disease digitalis is occasionally useful, but fails entirely in some cases. In exophthalmic goitre it is invaluable combined with quinine and iron. In cardiac dropsy digitalis is a thoroughly rational and highly successful remedy. In renal dropsy it is of great service, when this is acute, complicating scarlet fever, or due to failure of an hypertrophied heart. In dropsy from chronic tubular nephritis (large white kidney) it is rarely of use, as it has no influence on the renal cells.
Digitalis is used in hoemorrhage, but therapeutics is notoriously uncertain here. It will relieve haemoptysis due to mitral disease, or to the congestion of incipient phthisis in persons with languid circulation. For menorrhagia it may be useful by stimulating the uterine wall, or in the subjects of heart disease.
In secondary bronchial catarrh and acute pneumonia it acts entirely as a cardiac stimulant. Digitalis is but little used by English physicians as an antipyretic in fever, as it is slow, uncertain, dangerous, and unnecessary. Combined with quinia it is exhibited in phthisis, hut is apt to derange digestion. Empirically, in doses of several drachms, the tincture has been found useful in delirium tremens, but is unquestionably dangerous. Moderate doses are invaluable in the same disease, or in subacute or chronic cases of alcoholism, to stimulate the heart, relieve low sinking feelings, and rouse the appetite.
Traces of some of the active principles of digitalis have been detected in the urine. The action of the drug upon the urine, let it be carefully noted, is not due to any direct influence on the cells of the kidney, but to its effect chiefly on the heart and vessels generally, partly on the renal arteries.