Digitoxin is the name given to a natural substance found in the leaves of the red foxglove. It belongs to the cardiac glycosides.
What is digitoxin?
Digitoxin is a cardiac glycoside and has cardiac effects and ensures that the functions of the heart muscle are improved. Digitoxin is a cardiac glycoside that occurs naturally. For example, the active ingredient forms a component of the leaves of the red foxglove (Digitalis purpurea). The steroid glycoside is composed of the aglycone digitoxigenin, which has a linkage to three sugar residues. The glycoside has cardioactive effects and ensures that the functions of the heart muscle are improved. The red foxglove plant found medicinal use as early as 1775. One hundred years later, the German-Baltic pharmacologist Oswald Schmiedeberg (1838-1921) succeeded in isolating digitoxin for the first time. The physician Claude-Adolphe Nativelle carried out further research. By 1962, the structure of digitoxin had been completely deciphered. However, unlike digoxin, digitoxin is less commonly used to treat heart disease.
Pharmacological action
Digitoxin exhibits a positive inotropic effect on the muscles of the heart. As a result of the steroid glycoside binding to the ryanodine receptor, cytosolic calcium concentration improves. This leads to a more intense contraction of the cardiac muscle cells. It takes about three to four hours after taking the drug for digitoxin to exert its positive effect. The persistence of the positive effect varies between 7 and 12 hours. A more rapid effect can be achieved by immediate injection into the bloodstream. Thus, it sets in after only 25 minutes to 2 hours. The duration of action is then 4 to 12 hours. The effect of digitoxin is noticeable in that the cardiac output increases and the heart beats more slowly and more intensively. In addition, the overall blood circulation of the organism improves. In order to prevent overloading of the heart muscle, Digitoxin, like all other cardiac glycosides, is administered together with other medications, thus facilitating the heart’s additional work. These may be ACE inhibitors to dilate the vessels or diuretics to reduce the amount of fluid within the body. Digitoxin is also effective for cardiac arrhythmias in which the heartbeat is too fast. Because only seven percent of Digitoxin is excreted from the human body during the day, only a smaller dosage may be taken after the initial stage to ensure a stable Digitoxin level in the body. The drug is excreted primarily via the liver. Since this occurs independently of the kidneys, people can also use Digitoxin who do not have adequate kidney function. However, due to the slow elimination of the active substance from the body, care must be taken to avoid an overdose. There is a risk of poisoning in such a case.
Medical application and use
Digitoxin is administered in cases of heart muscle weakness. Thus, the drug causes more efficient work of the heart as well as increasing the strength of the heart. In addition, the drug is used in the case of cardiac arrhythmias such as atrial flutter or atrial fibrillation, which are associated with an acceleration of cardiac activity. In this case, the steroid glycoside lowers the heart rate. Another important area of application for digitoxin is chronic heart failure (cardiac insufficiency). This is particularly true if it is associated with renal insufficiency. The drug is also used in ophthalmology. There it is used for the treatment of accommodation disorders. Digitoxin is administered orally by tablets, topically as eye drops, or intravenously by injection solution.
Risks and side effects
Taking digitoxin may be associated with adverse side effects, but these do not automatically occur in every patient. The most common are nausea, vomiting, and lack of appetite. Also possible are occasional diarrhea, headache, abdominal pain, insomnia, nightmares, depression, confusion, lupus erythematosus, psychosis, hallucinations, thrombocytopenia (decrease in blood platelets), or enlargement of the mammary gland (gynecomastia). Extremely rarely, obstruction of the intestinal vessels may also occur.Contraindications to the use of digitoxin include acute myocardial infarction, myocarditis, ventricular tachycardia, ventricular arrhythmias, pulmonary disease, digitalisin intoxication, myxedema, and oxygen deprivation. If digitoxin therapy is given during pregnancy, it is important to consistently monitor the pregnant woman. There is a risk of interactions due to the simultaneous use of Digitoxin and other drugs. For example, the effect of the drug is enhanced by preparations that cause a deficiency of magnesium or potassium. These include the antifungal agent amphotericin B, diuretics (dehydrating agents), the endogenous hormone ACTH, the antibiotic penicillin G, anti-inflammatory salicylates and laxatives. Enzyme inducers such as the antibiotic rifampicin, the epilepsy drugs phenobarbital and phenytoin, the diuretic spironolactone, and the analgesic phenylbutazone threaten to shorten the positive effect of digitoxin.
