Synonyms
HerzglycosideDigitoxin is an active ingredient belonging to the group of cardiac glycosides. Among other things, it improves the efficiency of the heart and is therefore prescribed, for example, in cases of heart failure (cardiac insufficiency).
Origin
Digoxin and digitoxin can be extracted from the same plant: The foxglove (Latin: digitalis), therefore they are sometimes described synonymously with the term digitalis or digitalis glycosides.
Effect and mechanism of action
Digitoxin works on the heart as follows:
- Increase the contact force of the heart muscle (positive inotropic)
- Delayed transmission of excitation from the atrial region (antrum) to the ventricles (ventricles) (negative dromotropic)
- Reduction of the beat frequency (negative chronotropic effect).
Physiology
The increase of the contraction strength of the heart is achieved by the following mechanisms:
- Sodium–potassium ATPase – 3 sodium ions to the outside, 2 potassium ions to the inside (each against the natural concentration gradient, i.e. energy consuming)
- Sodium–calcium exchanger – 3 sodium per natural gradient inwards, 1 calcium against the natural gradient outwards.
- Cardiac glycosides – inhibition of sodium-potassium ATPase, thus less sodium outside. As a result, indirect inhibition of the sodium-calcium exchangers, which ultimately leads to increased intracellular calcium concentration.
Digoxin and digitoxin differ in their pharmacological properties. Digitoxin: Its bioavailability when taken as a tablet is almost 100%. It is excreted partly through the kidney (renal) and partly through the liver (hepatic). Its half-life is 5-7 days.
Indications
Digitoxin is used for the following indications:
- Heart failure (pumping weakness of the heart)
- Atrial flutter and flicker (due to the delay in excitation transfer)
Digitoxin has a narrow therapeutic range. This means that it is very easy to overdose, which leads to intoxication. This is because inhibition of the sodium-potassium pump must always be done in moderation, otherwise the entire cell stability will be shaken. Symptoms of an overdose can be the following: The therapy of digitoxin intoxication consists of the administration of potassium-containing infusion solution (since an increased potassium concentration displaces the cardiac glycosides from the sodium-potassium ATPase and thus inhibits their effect), antiarrhythmics (drugs that limit the cardiac arrhythmia that may be triggered), digitalis antibodies (which capture specifically free cardiac glycoside molecules and thus render them ineffective).
- At the heart: cardiac arrhythmia such as ventricular fibrillation, extrasystoles in the chamber muscles, AV block
- In the central nervous system: color vision disorders, fatigue, states of confusion
- In the gastrointestinal tract: nausea, vomiting
