Digitalis (Lat, digitalis), or foxglove, is the dried leaves of Digitalis purpurea (Fam. Scrophulariaceae). It is an ornamental flower of the gardens, grows wild in Europe, Oregon, and Australia, and is cultivated for the drug market in England and Germany. The wild American plant has been found efficient.

Constituents

The active principles are glucosides, and are, therefore, subject to ready destruction. Digitoxin, which most nearly represents the digitalis action, is practically insoluble in water, but soluble in alcohol. It is present to the extent of 0.2 to 0.4 per cent. Digitalin, next in importance, is slightly soluble in water, soluble in 100 parts of diluted alcohol, and readily in alcohol. Digitalein, of similar nature, is soluble in both water and alcohol. Under the influence of heat or acids, or when kept some time in aqueous solution, as in the infusion, these glucosides tend to decompose, and may form toxiresins which have a central convulsant action.

In addition to these active principles, digitalis contains digitonin, a saponin body which foams with water and possesses the peculiar property of holding the otherwise insoluble active principles in solution in water. It is on account of this that the infusion of digitalis, an aqueous preparation, represents the activity of the drug. Digitonin, administered intravenously, is a physiologic antagonist of digitoxin; but it is not absorbable from the alimentary tract. It crystallizes from solutions in alcohol of over 85 per cent. strength. Besides these principles, digitalis contains an acrid, nauseating substance, digitalosmin, free oil, and digitaleic acid.

Preparations And Doses

Official

Digitalis, dose, 1 grain (0.06 gm.). Fluidextract, 1 minim (0.06 c.c.). Tincture, 10 per cent., 10 minims (0.6 c.c.). Infusion, 1.5 per cent., 1 dram (4 c.c.). The doses above may be increased up to four times as much in serious cases. The Pharmacopoeia requires a biologic assay for all digitalis preparations.

Unofficial

Digitoxin, dose, 1/120 grain (0.0005 gm), is too irritating for hypodermatic use, but may be used by mouth or intravenously.

Digitalin, dose, 1/10 grain (0.006 gm.), is moderately irritating, but can be used hypodermatically. (See page 161.)

Digalen, made according to Cloetta's formula, is a proprietary remedy which, it is claimed, contains 1/225 grain (0.3 mg.) of digitoxin in each 15 minims (1 c.c.), the solvent being alcohol, glycerin, and water. A number of investigators believe that this is not digitoxin, but probably digitalein. It is moderately irritating, but has been used intravenously. Laboratory experiments show its action to be very variable.

Digipuratum, made according to Gottlieb's formula, is an extract freed from digitonin and most of the extractive matter, and mixed with sugar of milk to form a powder of the same strength as digitalis leaves. Worth Hale and others have found it a good preparation. In our own experience it is exceedingly uniform. It is marketed in tablet and in 0.1 per cent. solution of sodium bicarbonate. The tablets are equivalent to 1 1/2 grains (0.1 gm.) of digitalis. The liquid form is for intravenous or hypodermic use, 15 minims (1 c.c.) being equivalent to 1 1/2 grains (0.1 gm.) of digitalis. Digifolin is a similar preparation of the same strength.

Eggleston finds that the total amount to develop effects is the same whether given at one time or in repeated doses. From the large doses the average time to obtain an action was twenty-eight hours, and from the smaller repeated doses, seventy hours. He found that the full dose was about 2 minims (0.146 c.c.) of the tincture, or 1/2800 grain (0.023 mg.) of digitoxin, by mouth, per pound of body weight.

In a comparative test by Edmunds the infusion and the tincture were found of equal efficiency when given in doses corresponding with the amount of digitalis used in their making. Focke (1909), however, found the infusion regularly about 20 per cent. weaker than the powdered leaves; and, because of the method of its manufacture, it is probable that this is usually the case. The tincture and infusion are the best official preparations. The author has frequently seen the infusion prescribed in half-ounce doses. This is equivalent to 36 minims of the tincture, and is a large dose; but it is probable that in serious cases the best results are obtained only when such very large amounts are employed at the outset. The effects of these large doses of the infusion have frequently been compared with those from small doses of the tincture, naturally to the disadvantage of the latter. The author is informed that when the infusion is prescribed a number of druggists dispense a diluted fluidextract, a most reprehensible practice.

The fluidextract is a concentrated preparation with a small dose, and to its use there are the following objections: (1) On account of the small amount of solvent, there is uncertainty that all the active principles of the drug are extracted in the preparation; (2) precipitation is likely from inability of the solvent to hold so much dissolved matter; (3) deterioration is more likely, as the solvent is insufficient to act as a preservative; (4) very slight evaporation materially changes the strength of the preparation; and (5) owing to the smallness of the dose, it is difficult to grade the dosage. As a matter of fact, Worth Hale had digitalis leaves made into tincture and fluidextract, and found the latter only about three times as strong as the former, instead of ten times, as it should be. Assays of commercial preparations have given similar findings. Hence the fluidextract should be abolished.