Cardiac glycosides are one of the most potent substances of plant origin on humans. Their basic action is to slow down the heart rate and increase the strength of its contraction. It makes the heart work harder and definitely more efficiently. How do cardiac glycosides work? What are the indications and contraindications for their use?

Cardiac glycosideshave historically been used as primary medications in the treatment of heart failure from a variety of causes. However, these are so strong compounds that their use carries a high risk of dangerous and unpredictable side effects.

Modern research has shown that the benefits of their use are not significantly greater than in the case of using new, definitely safer for the human body groups of drugs.

Therefore, this once very important and frequently used group of plant active substances is now much less important in medicine - cardiac glycosides are now used only in combination with other drugs, and also, for example, in a pharmacy formula in the form of a tincture from the lily of the valley.

Cardiac glycosides - occurrence in nature

Cardiac glycosides are produced by plants such as:

  • sea onion
  • purple foxglove
  • spring love
  • woolly foxglove
  • lily of the valley

It should be remembered that these plants are poisonous to such an extent that in the old days they were used successfully as, for example, poison on rodents. Even a single swallowing of a small piece of the plant can be dangerous, especially for young children and animals, and unfortunately toxic glycosides accumulate in the body.

How do glycosides work?

The principle of action of glycosides is based on:

  • inhibition of the sodium-potassium pump in the cells of the heart muscle. This increases the intracellular concentration of sodium and calcium, thereby increasing the strength of heart contractions
  • activating the sympathetic nervous system. There is an increase in the vagal nerve tension, which inhibits the function of the sinoatrial and atrioventricular nodes and their rhythm slows down, which in simplified means that the heart starts beating more slowly

In other words, cardiac glycosides have the following effect:

  • positive inotropic (this means an increase in the force of contraction)
  • chronotropic negative (i.e. reducing the frequency of contractions)
  • dromotropic negative (inhibition of heart conduction)
  • batmotropic positive (increase in excitability threshold)

Cardiac glycosides - digoxin

Digoxinis an organic chemical compound from the glycoside group, isolated from foxglove ( Digitalis lanata ). Digoxin, like other cardiac glycosides, works by blocking the sodium-potassium pump present in the cell membrane of the heart cells.

Digoxin increases the force of contraction of the heart muscle while slowing down the heart rate. The main use of digoxin is in the treatment of atrial fibrillation, but it can also be helpful in managing the worsening symptoms of severe heart failure. However, in case of failure, it is only used as supportive treatment.

Contraindications to the use of digoxin

Despite therapeutic indications, digoxin may not be used in all patients and in every patient. Contraindications are:

  • allergy (hypersensitivity) to the active substance or any of the other ingredients of the drug and other cardiac glycosides
  • arrhythmia
  • ventricular tachycardia and fibrillation

Particular care should be taken when using digoxin if the patient has:

  • heart failure due to vitamin B1 deficiency (beriberi disease)
  • low potassium or magnesium levels in the blood
  • high levels of calcium in the blood
  • kidney problems
  • digestive disorders
  • thyroid disease
  • lung diseases

However, if the administration of the drug is nevertheless necessary - and this also happens, the patient's condition should be regularly monitored.

Pregnancy and lactation and digoxin therapy

The use of digoxin during pregnancy is not absolutely contraindicated, but the dosage may be more difficult to determine, and side effects are sometimes unpredictable.

The use of digoxin in pregnant women is permitted only if the benefit to the mother outweighs the potential risk to the fetus.

Digoxin is believed to be the cause of prematurity and low birth weight in babies by directly affecting the uterine mucosa.

Maternal Digoxin can be used to treat fetal tachycardia and congestive heart failure. A pregnant woman must, howeverbe under the constant care of a specialist.

According to research, digoxin is excreted in breast milk in minimal amounts, which has no effect on the circulation and heart rhythm of the newborn, therefore breastfeeding is not contraindicated.

Digoxin - side effects

Like all drugs, digoxin can also cause side effects, but remember that not everyone will experience them, and their intensity may vary. The most common side effects include:

  • nausea
  • stomach pains
  • vomiting
  • anorexic
  • dizziness
  • headache
  • fainting
  • weakness
  • insomnia
  • visual disturbance (blurred or yellow, green or purple vision)
  • mental disorders
  • hallucinations
  • delirium
  • depression
  • convulsions
  • potassium and calcium metabolism disorders in the body

Digoxin - interactions

During treatment with digoxin, it should be remembered that it may have numerous interactions. Therefore, when taking digoxin, tell your doctor about all other medications you are taking, even those over the counter.

Drugs that should not be combined with digoxin are:

  • diuretics - hydrochlorothiazide, spironolactone, furosemide - possible significant drop in blood pressure (even life-threatening) and aggravation of arrhythmia
  • angiotensin converting enzyme inhibitors (e.g. captopril) - increase the concentration of digoxin in the blood serum, and thus increase the likelihood of drug overdose or side effects
  • macrolide antibiotics (e.g. clarithromycin), tetracyclines - reduce the concentration of digoxin
  • calcium - risk of arrhythmias; hypercalcemia increases the risk of digoxin poisoning
  • potassium s alts used together with digoxin may lead to hyperkalemia

Digoxin - interactions with food

  • licorice - while taking the drug, you should limit the consumption of products that contain it, even in the form of candies or tea. The active substance in licorice may increase the risk of excessive slow heart rate and dangerous arrhythmias
  • fiber - reduces the absorption of the drug from the gastrointestinal tract, which in turn leads to a reduction or complete absence of the therapeutic effect. Therefore, during treatment with digoxin, care should be taken not to consume it in excess, especially if it is additionally taken in the form of supplements
  • St. John's Wort - tincture or tea of ​​St. John's wort, often used for the purposeto relieve stress or as a hypnotic, may reduce the effectiveness of digoxin

Cardiac glycosides - methyldigoxin

Methyldigoxinis an organic cardiac drug from the glycoside group, digoxin methyl ester. It increases the stroke capacity of the heart, slows down the heart rate, lowers venous pressure and increases blood pressure, which improves the efficiency of the heart.

Increases glomerular filtration and the amount of urine excreted from the body. Due to the fact that it is fat-soluble, it is better absorbed than digoxin.

Methyldigoxin - indications for use

  • atrial fibrillation with rapid ventricular activity in the course of heart failure.
  • advanced systolic, chronic congestive heart failure in combination with other medications
  • heart defects

Methyldigoxin - contraindications to use

  • hypersensitivity to cardiac glycosides or any of the ingredients of the preparation
  • sinus node dysfunction in patients without a pacemaker
  • ventricular tachycardia, ventricular fibrillation
  • hypokalemia, hypomagnesaemia, hypercalcemia and other fluid and electrolyte disturbances
  • suspected digitalis glycoside poisoning

Methyldigoxin - interactions

Methyldigoxin may interact with drugs such as:

  • drugs that increase the concentration of potassium (spironolactone, potassium s alts) reduce the positive inotropic effect of methyldigoxin and increase the risk of arrhythmias
  • drugs affecting the electrolyte balance, e.g. some diuretics, laxatives, benzyl penicillin, cotricosteroids, salicylates, lithium s alts increase the toxicity of methyldigoxin
  • Sympathomimetic amines (including salbutamol) may increase the risk of arrhythmias
  • antacids, activated charcoal, pectins, some laxatives may reduce the absorption of the drug, so remember to keep a two-hour interval after methyldigoxin

Methyldigoxin - side effects

The side effects of methyldigoxin mainly affect the gastrointestinal tract, central nervous system and heart. The most common:

  • appetite reduction
  • nausea
  • insomnia
  • headache
  • constant fatigue

Sometimes there are also:

  • allergic reactions (hives or scarlet fever rash)
  • blush
  • lupus erythematosus
  • nightmares
  • arousal
  • entanglement
  • depression
  • hallucinations

Glycosides - poisoning

During glycoside therapy, remember to follow your doctor's recommendations, do not modify the dose yourself, and certainly not increase it. Poisoning with glycosides can be manifested by:

  • nausea, vomiting, stomach pain, diarrhea
  • color vision disorders (seeing first "purple" then "yellow")
  • other visual disturbances (blurred vision, double vision, and even temporary blindness)
  • difficult to control and life-threatening arrhythmias
  • disturbance of consciousness, confusion

Symptoms of overdose often disappear simply by stopping the drug. However, it all depends on the size of the dose taken, other medications taken at the same time, and comorbidities.

The management of an overdose of cardiac glycosides includes:

  • supplementing the deficiencies of magnesium and potassium ions, most often in the form of a drip
  • giving activated charcoal with a laxative
  • in bradycardia (i.e. when the heart rate is too slow and is below 60 beats per minute) atropine is administered
  • in very severe poisoning, specific antibody fragments that bind digoxin in plasma are used
  • in conduction disorders it is recommended to implant a temporary pacemaker

That is why it is so important to monitor your body while taking glycosides, and immediately report any disturbing symptoms to your doctor.

About the authorKarolina NowakA pharmaceutical technician by education. Currently, he is professionally fulfilled working in a pharmacy. Empathetic, sensitive and fond of contact with other people. Privately, a lover of a good book.

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