Digitalis Leaf (B.P., I.P.). Digit. Fol.; Digitalis; Foxglove Leaf; Feuille de Digitale; Fingerhutblatt; Hoja de digital.
Dose: See under Uses.

Foreign Pharmacopoeias: In all pharmacopeias examined, most of which specify not less than 10 units per g.

The dried leaves of Digitalis purpurea (Scrophulariaceae). Digitalis leaf contains a number of glycosides, including digitoxin, gitoxin, and gitalin. Aqueous preparations of digitalis, such as infusions and mixtures, are very unstable. Protect from light and moisture.

Note. When Digitalis, Digitalis Folii Pulvis, Digitalis Folium, Digitalis Leaf, Powdered Digitalis Leaf, or Pulvis Digitalis is prescribed, Prepared Digitalis is dispensed.

Nausea, salivation, vomiting and anorexia are among the earliest symptoms of digitalis overdosage; diarrhoea and abdominal pain may also occur. Certain cerebral effects are also early symptoms of digitalis overdosage; these include headache, malaise, drowsiness, disorientation, mental confusion, and aphasia. Blurring of vision may occur, and there may be disturbance of colour vision, objects appearing yellow or green. Various disturbances of cardiac rhythm occur as a result of over dosage and the development of extra systoles, pulsus bigeminus, partial or complete heart-block or ventricular tachycardia are indications for discontinuing treatment; ventricular fibrillation is the commonest cause of death from digitalis poisoning. Toxic reactions to the drug may be precipitated if there is potassium depletion, which may be caused by mercurial diuretics.

Potassium salts should be administered orally, usually as the acetate or chloride, in doses of 2 to 10 g. daily if renal function is normal. Ventricular arrhythmias refractory to potassium may be controlled by intravenous injection of 15 to 20 ml. of a 20% solution of magnesium sulphate, but owing to its unpleasant side-effects, the use of magnesium sulphate should be confined to refractory arrythmias. When renal function is impaired and the use of potassium salts contra-indicated, procainamide hydrochloride may be given orally in doses of 0.5 to 1 g. every four to six hours, but it should be used with caution, and intravenous administration should be reserved for critically ill patients.

heart failure ensues. In shock or in peripheral circulatory collapse occurring in the course of acute infectious diseases, digitalis may further decrease cardiac output and thus aggravate the syndrome.

The most important indication for the use of digitalis is congestive heart failure. The increased force induced by digitalis results in more complete emptying of the ventricle at systole, and correspondingly greater output per beat. Venous pressure is lowered because the heart is capable of dealing with an increased venous return of blood. Not only is the force of systole increased, but its length is shortened, giving the heart more time to rest between contractions and more time for the ventricle to fill with venous blood.

Owing to the increased cardiac output there is improvement in the peripheral circulation, with mobilisation of oedema fluid, improved renal blood flow, and resultant diuresis. Since the diuretic action of digitalis is entirely the result of its action on the heart and circulation, the drug will not improve renal function unimpaired by faulty circulation, or remove oedema not due to heart failure.

Auricular fibrillation was at one time thought to be the main indication for the use of digitalis; it is now appreciated that it is the cardiac failure and not the disordered rhythm which is of primary importance. If there is no heart failure little effect on the ventricular rate may he noted; indeed, in toxic cases without failure, as in thyrotosicosis and diphtheritic heart disease, it may even be harmful.

It is in auricular fibrillation due to congestive heart failure that digitalis produces its most dramatic results. In the majority of cases, the abnormal rhythm is not abolished but the ventricular rate is slowed, and owing to the cardiovascular action of the drug there is an increase in the force of ventricular systole, the combined action resulting in a general improvement in the condition.

Digitalis is also used to convert auricular flutter to auricular fibrillation; on cessation of digitalis therapy normal sinus rhythm may be restored.

In paroxysmal auricular tachycardia, digitalis may relieve or prevent an attack, but in paroxysmal ventricular tachycardia its use is dangerous even in undigitalised patients, and is indicated only if heart failure develops.

Blood pressure is affected by digitalis only through the action of the drug on the heart and not by any significant effect on the blood vessels or vasomotor centre; low pressures due to decompensation are raised to normal as digitalis improves cardiac function.

Digitalis is eliminated slowly from the body, and with repeated doses cumulative effects occur, eventually resulting in digitalis poisoning. It is therefore important to know before administering the drug whether a patient has previously been receiving digitalis. A single dose of digitalis given by mouth is usually absorbed within 2 hours and exerts its full action on the heart within 6 hours, the cardiac action persisting for several days to 3 weeks or more.

The patient may be digitalised more slowly by giving the total dose in divided doses spread over 2 to 4 days, usually m doses of 200 mg. (3 grains) of prepared digitalis or 2 ml. (30 minims) of the tincture three times daily for 2 days, then half or two-thirds of that dosage for 2 or 3 days.

The effects of digitalis can only be maintained when the drug is given in excess of the amount excreted daily-. It is impossible to employ any rule of thumb method in assessing the daily maintenance dose required as it varies with each patient and depends on the level of digitalis action desired. It is usual to aim at a constant concentration of digitalis in the system sufficient to Produce a pulse-rate of approximately 60 beats per minute. This is usually achieved by a dosage of the order of 60 to 200 mg. (1 to 3 grains) daily of prepared digitalis, or of 0.6 to 2 ml. (10 to 30 minims) of tincture.

If digitalis cannot be given orally the tincture may be given by rectal injection, or suppositories of powdered digitalis may be employed; the doses, intervals between doses, and the time necessary to obtain cardiac effects are the same for rectal as for oral administration. In cases of acute emergency an intravenous injection of digoxin may be given; this produces an effect on the heart-rate within 15 to 30 minutes.

Foreign Pharmacopoeias: Similar standardised powders
(10 units per g.) are included in Egyp., Ind., Alex., Span., Swiss, and U.S.

Digitalis leaf reduced to powder, no part being rejected, and biologically assayed the strength being stated in units per g. For therapeutic purposes it must be adjusted to contain 10 units in 1 g. (1 unit in 100 mg.). It may be adjusted by admixture with a weaker prepared digitalis, with the dried exhausted marc from the preparation of Tincture of Digitalis, with powdered lucerne, or with powdered grass. I.P. allows admixture with rice starch. Protect from moisture.

The infusion has such practical disadvantages that its use should now be abandoned.-C. Hoyle and J. W. Linnell, Practitioner, 1936, 136, 94.

Dose: 15 ml (0.5 fl oz.) twice or thrice daily in water, as directed.

Mist. Digital. et Caffein. (N.F. 1939). Tincture of digitalis 7.5 m., caffeine 1 gr., solution of strychnine hydrochloride 3 m., concentrated infusion of orange peel l. m., water to 0.5 fl oz. Dose: 15 ml. 0.5 fl. oz.).

Mist. Digital. c, Scill. (N.F. 1939). Tincture of digitalis 5 m., tincture o( squill 10 m., potassium acetate 10 gr., chloroform water to 0.5 fl oz. Dose: 15 ml. (0.5 fl oz.).

Tablets of Prepared Digitalis (B.P.). Tab. Digit. Praep.; Tab. Digit. (B.N.F.); Digitalis Tablets Unless otherwise specified 1-grain tablets are supplied. U.S.P. usual strength,: 30, 60, and 100 mg. Protect from moisture.

Digitalis Tincture (U.S.N.F.). Prepared from digitalis, about 1 in 10, by percolation with a mixture of alcohol l vol. and water 1 vol., and adjusted to contain 1 unit per ml. Dose: 1 ml. 5 to 15 minims).
Similar tinctures are included in most foreign pharmacopoeias.

Tincture of digitalis prepared by 1-hour maceration-gentle agitation of powdered digitalis with 10 volumes of alcohol (70%)-retains its potency for at least 5 days and it is recommended that such a preparation be made extemporaneously from standardised leaf powder when tincture of digitalis is prescribed.- J.M. Rowson, J. Pharm. Pharmacol., 1955, 7, 924.

Related Links
Foxglove Monograph