How digitoxin works
Digitoxin inhibits an enzyme (the magnesium-dependent Na/K-ATPase) that is anchored in the cell membrane and carries sodium ions out of the cell and, in turn, potassium ions into the cell. As a result, the sodium concentration inside the cell increases, while at the same time the potassium concentration inside the cell decreases.
The increased sodium concentration now influences the sodium/calcium exchanger, which now transports fewer calcium ions out of the cell. As a result, more calcium ions are stored in the so-called sarcoplasmic reticulum (a compartment within the cell) during the relaxation phase (diastole) of the heart.
If the heart now contracts (systole), correspondingly more calcium ions are released from the store. In this way, digitoxin increases the contractile force of the heart muscles (positive inotropic effect).
Absorption, degradation and excretion
Digitoxin is usually taken by mouth (oral administration), sometimes administered directly into a vein (intravenous administration). After oral administration, the active substance is almost completely absorbed into the blood in the digestive tract.
The effect of the cardiac drug sets in after about 20 to 120 minutes with intravenous administration, and only a little later with oral administration. A large proportion is metabolized in the liver.
Digitoxin remains in the body for a very long time. Only six to eight days after administration is half of the active substance excreted again (elimination half-life). Sixty percent is excreted in the urine and 40 percent is excreted in the stool via the bile.
When is Digitoxin used?
Digitoxin is used for:
- Acute and chronic heart failure (congestive heart failure)
- @ Atrial fibrillation
How Digitoxin is used
Digitoxin is usually prescribed as a tablet. The dosage is determined on an individual basis.
Effect and side effect are very close together with cardiac glycosides such as digitoxin. For this reason, the concentration in the blood is determined at regular intervals to find the optimal maintenance dose.
What are the side effects of Digitoxin?
The main side effects of Digitoxin include cardiac arrhythmias, headache, drowsiness, impaired color vision (yellow vision), nausea, and vomiting.
Other adverse effects are also possible such as confusion, agitation, acute psychosis, delirium, epileptic seizures, skin rash, enlargement of the mammary glands in men (gynecomastia), and a decrease in the number of blood platelets (thrombocytopenia).
What should be considered when using digitoxin?
Contraindications
Digitoxin should not be used in the following cases:
- Known hypersensitivity to Digitoxin.
- Dilated cardiomyopathy (abnormal enlargement of the heart muscle)
- Chronic cor pulmonale (“pulmonary heart”)
- Increased or decreased blood potassium levels (hyper-/hypokalemia).
- Certain forms of cardiac arrhythmia
Drug interactions
Digitoxin may interact with other drugs taken at the same time. This may affect the effect and side effects of the heart medicine or the other medicines.
For example, concomitant use of certain diuretics (kaliuretic diuretics) or corticosteroids (“cortisone”) increases the risk of cardiac arrhythmias.
In case of simultaneous use of activated charcoal (in case of diarrhea or poisoning) or cholestyramine (cholesterol-lowering agent), it may be necessary to increase the digitoxin dose. The same applies if rifampicin (antibiotic) or phenobarbital (for anesthesia and against epilepsy) is used in addition to the cardiac drug. Interactions may also occur with simultaneous administration of beta-blockers (cardiovascular drugs).
Age restriction
Digitoxin can be used from birth if indicated.
Pregnancy and lactation
Cardiac glycosides such as Digitoxin may be used during pregnancy in cases of cardiac insufficiency and as an antiarrhythmic agent for the mother or the unborn child.
If possible, other agents (such as acetyldigoxin, digoxin) should be used during breastfeeding. If it is necessary to use Digitoxin, it should be decided on a case-by-case basis whether the woman must wean beforehand.
How to obtain medication with Digitoxin
Digitoxin requires a prescription in Germany and Austria and is therefore only available from pharmacies on presentation of a doctor’s prescription. In Switzerland, there are currently no preparations with Digitoxin on the market.