Digitalis drugs: indications, examples, mechanism

Used for more than 200 years in cardiology, digitalis are ancient remedies of natural origin, derived from a plant with powerful but also very toxic properties.

Definition: what is digitalis?

A digitalis is a compound derived from digitalissubstance derived from a plant: foxglove (Digitalis purpurea). In medicine, digitalis are a class of drugs used in cardiology, called cardiac glycosides. They are constraining molecules because of their side effects, their risk of intoxication and their narrow therapeutic windowwhich involves regularly monitoring their dosage, tolerance and toxicity. Blood tests are also recommended to check the level of potassium in the blood (kalaemia) which may be responsible for heart problems. Digitalis can interact with many drugs, which makes their use all the more delicate. In the event of digitalis poisoning, there are antidotes such as atropine, phenytoin, lidocaine or specific monoclonal antibodies Fab.

Digitalis purpurea or purple foxglove © terezie-123RF

What are the indications for digitalis?

Digitalis (mainly digoxin) may be indicated in case of’heart failure or heart rhythm disturbances (slowing down of atrial fibrillation in particular).

What is the mechanism of action of digitalis?

digitalis increase the strength of contraction heart muscle (positive inotropic effect), decrease heart rate (negative chronotropic effect), slow electrical conduction between the ventricles and the atria (negative dromotropic effect) and increase the excitability of the muscle fibers of the heart (positive bathmotropic effect). They have the effect ofincrease cardiac output in heart failure and to decrease sympathetic tone. They exert their action by inhibiting an enzyme in the form of a pump (Na+/K+ ATPase) located on the cell membrane, and whose role is to regulate the electrical polarization of the cell by passage and retention of ions. A sudden depolarization of the cell leads to muscle contraction, which lasts all the longer as the depolarization is prolonged. The pump must then repolarize the cell in order to stop the contraction of the muscle, to then allow the arrival of a new contraction. by depolarization. Under the action of digitalis, the pump cannot exercise its role correctly, which has the effect on the one hand of increasing the force of muscular contraction, and on the other hand of delaying the onset of the next cardiac contraction.

Examples of the main digital technologies in France

In the past, digitalis such as digitoxin (or digitalis), digoxin, deslanoside or metildigoxin were used for the development of drugs for cardiology. Due to their significant toxicity in the event of an overdose (the therapeutic dose being very close to the toxic dose), they have gradually been eliminated in favor of more recent and better tolerated treatments. Today the digoxin is the only digital still marketed in France. Digoxin is found in medications Digoxin Nativelle® (drinkable drops, solution for injection and tablets) as well as in the medicine Hemigoxin Nativelle® (tablets).

In case of overdose, it is imperative to stop digitalis and rest

What are the side effects of digitalis?

Digitalis are generally well tolerated at therapeutic doses. On the other hand, due to their narrow therapeutic range, Signs of overdose (toxicity) are common. These side effects can be:

  • of the heart trouble with disturbance of theEKG and can be serious or even fatal (example: ventricular hyperexcitability),
  • of the digestive disorders such as nausea, vomiting and diarrhea
  • of the visual disturbances with yellow coloration (especially in the elderly)
  • of the seizures
  • of the delusions
  • of the hallucinations
  • of the psychoses in very old people.

Rare manifestations such as gynecomastia, allergies and thrombocytopenia declare themselves exceptionally. In case of overdose, it is imperative to stop digitalis and rest. Do not take other cardiology medications without medical advice. Antidotes can be taken in case of a large overdose, as decided by a doctor.

What are the contraindications of digitalis?

The contraindications of digitalis (digoxin) are: atrioventricular blocks 2nd and 3rd degree not fitted, ventricular hyperexcitability (example: extrasystoles), ventricular tachycardia and fibrillation as well as hypokalemia (insufficient potassium level) not corrected. Digitalis should never be given at the same time as treatment with St. John’s wort, sultopride or intravenous calcium salts. Many other drugs interact with digoxin without however constituting strict contraindications, although increased monitoring is necessary (such as bradycardiac drugs, midodrine, amiodarone, oral calcium, carbamazepine, clarithromycin, erythromycin, sulfasalazine, sucralfate, charcoal, antacids and gastric protectors, ritonavir, hypokalaemic agents or drugs at risk of torsades de pointes). Also, precautions for use are imperative in case of’renal failure severe, severe hepatic impairment, hypoxia due to respiratory failurehypothyroidism or hypercalcemia, advanced heart failure, electrolyte disturbances as well as in case of general anesthesia.

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