The well dried leaves of Digitalis purpurea, native of Great Britain, and cultivated in this country.
The active principle, digitalin, is one of several important and complex principles of difficult analysis. Digitalin is no longer official, the preparations made from the whole leaf being considered more trustworthy.
The most important action of digitalis is as a heart stimulant and tonic, and is shown in the slowing and strengthening of the pulse. This is partly brought about by a direct action on the heart-muscle, by which the circulation in the organ itself is more efficiently carried on; partly by a strengthening of the inhibitory apparatus, which tends to slow the heart; and partly by a stimulant action on the vaso-motor system, by which the arteries are more strongly contracted, and, by offering some resistance to the force of the heart, excite it to greater effort. The result of all this is, that the diastole is lengthened, and the systole becomes more energetic. Thus the ventricles are better filled and more thoroughly emptied, and the beats, reduced in number, gain in firmness and strength.
When an excessible amount is taken, signs of overstimulation appear, marked by intermittency of the pulse or by a fall below normal; it may be to 40 or 50 in a minute. In this condition any sudden exertion, such as sitting upright, may bring to a climax the growing exhaustion of the heart, and the pulse may run up to 150 or more, becoming small, weak, and irregular. For this reason patients taking digitalis continuously must be kept quietly in bed and not allowed to sit up or to make any sudden exertion.
In taking it only occasionally or for a short time there is not the same danger.
Digitalis is also a diuretic, acting through an influence on the renal as well as on the general circulation, and for this purpose it is also used locally in the form of poultices applied over the kidneys, and made from the leaves or with the fluid preparations. Digitalis is eliminated by the urine, and much more slowly than it is absorbed into the system. For this reason, if doses are given close together, part of the influence of one may be added to that of the next, and the action is intensified by so much. But except conditionally in this way, a cumulative action of the drug is not acknowledged by all authorities.
In cases of poisoning the symptoms begin with violent and repeated vomiting of mucus and bile. There is a feeling of vertigo, pain, and heat in the head, and disturbance of vision, fringes of color with a vibratory motion being sometimes seen around objects.
The face is pale, the eyes staring and prominent, with dilated pupils and a blue color of the sclerotics.
There is sometimes salivation, and usually diarrhoea. The urine may be suppressed. The vomiting continues, and great prostration follows. The pulse is irregular, small, and weak, yet the beat of the heart may be hard and strong. The respirations become rapid and feeble. Pains in the limbs and back may be present. There are, usually before the end, delirium and stupor, or convulsions. Death occurs from general failure of the circulation with final paralysis of the heart, and has taken place as soon as three quarters of an hour after taking the poison. The average time, however, is one or two days. Digitalis poisoning of an acute form is not common, and in the majority of cases the patient recovers. The smallest fatal dose is not known. Twenty grains of the extract are known to have caused death in ten days.
Emetics and cathartics must be given, and tannin in large quantities. Alcoholic stimulants are used, but with great care, and the most perfect rest and quiet, with a perfectly horizontal position, maintained.
Digitalis is very bitter, nauseating, and irritant to the stomach, and is apt to interfere with digestion, and to cause vomiting, with occasional diarrhoea, marked by green discharges. These two latter symptoms may also be produced by hypodermic administration of the drug.
Headache and vertigo, fainting, sneezing, and buzzing in the ears, are caused by overdoses; also sparks before the eyes and other disturbances of sight; sleeplessness; fall of temperature; and irregularity or threadiness of the pulse.
Recent experiments prove that digitalis does not increase the strength or force of the heart's beats, but simply the extent of the contraction is increased. The heart cavity is more nearly closed and the contraction of the heart-muscle is more nearly complete than is normally the case.
Hypodermic injections of digitalis or of strychnine act in case of shock by a redistribution of the blood in different parts of the body, thus restoring function. Digitalin has been used in cases where digitalis cannot be taken by mouth. Dose, 1/50-1/75 gr. American digitaline, or 1/12-1/2 gr. Merck's German digitaline, injected deep into the muscles of the thigh, which are then to be rubbed thoroughly for at least five minutes to hasten absorption and prevent abscess formation.
More diuretic than stimulant. To be largely diluted. Average dose, ʒ 1-4 mils.
Strength, 10%. Average dose, viii.-0.5 mil.
The tincture and fluidextract are more stimulant than diuretic, and are only slightly diluted when given.
The variability of different preparations of digitalis, resulting in disappointing or in injurious action when prescribed in medicine, has caused the narrowing down to the now brief list of official preparations of the drug.
Digitalin was formerly recognized by the U. S. P. It has been used hypodermically, but was found to be irritating and liable to cause abscesses. This, with the uncertainty of exact composition brought it into disfavor, and artificial preparations are equally unsatisfactory.