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Cardiac glycosides – effect, application & risks

Cardiac glycosides

Cardiac glycosides are drugs that have a positive effect on the heart ‘s ability to beat while reducing the heart rate. They are used to treat heart disease .

What are cardiac glycosides?

Cardioactive glycosides are active substances whose effect relates to the heart. From a chemical point of view, the active ingredients are characterized by three deoxysugars that only occur very rarely in nature. These deoxysugars are attached to a steroid derivative in a glycosidic bond. The glycoside bond is also partly present in gonane derivatives.

Cardiac glycosides are often referred to as digitaloids or simply as digitalis . This designation is based on the foxglove (digitalis), which contains cardiac glycosides in quite high doses.

Only digitoxin and digoxin are clinically used today . Digitoxin is a steroid glycoside from the drug class of cardiac glycosides. It is obtained from the red foxglove (Digitalis purpurea). Digoxin is also a digitalis glycoside from foxgloves. Digoxin and digitoxin belong to the endogenous glycosides. This means they act as hormones . In humans, digoxin is produced in small amounts in the adrenal glands .

Cardiac glycosides are used primarily in the treatment of acute and chronic heart failure . They are also used in the treatment of atrial fibrillation and atrial flutter .

Cardiac glycosides are usually administered in the form of tablets. Only strophanthin is given intravenously due to the poor absorption rate. The substances are excreted mainly via the liver and bile .

Pharmacological action

Cardiac glycosides show a positive inotropic effect. The term inotropy is used to describe the influence on the contractility of the heart muscle tissue. With a positive inotropy, the contractile force of the heart is increased. This increase is based on an increased supply of calcium ions in the heart muscle cells. In return, the cardiac glycosides bind to the α-subunits of the sodium-potassium ATPase and thus inhibit the active transport of potassium ions into the cell . At the same time, the outflow of sodium ions from the cell is impeded. The sodium concentration inside the cell increases. As a result, the sarcoplasmic reticulum , a special form of theendoplasmic reticulum within muscle cells, calcium ions accumulate. These calcium ions are available to the heart muscle for contraction, increasing the force of contraction.

At the same time, cardiac glycosides also have a negative dromotropic effect. They decrease nerve conduction velocity . This effect is achieved by increasing the initial potassium outflow from the muscle cell. Due to the slowed transmission of stimuli, the heart contracts less frequently. This allows for a stronger contraction with more ejection volume.

Cardiac glycosides also show a positive bathmotropic effect. The influence of stimulation thresholds and the excitability of the heart is referred to as bathmotropia. Positive bathmotropic substances lower the excitation threshold, allowing the heart to contract more easily.

Medical Application & Use

The main areas of application for cardiac glycosides are acute and chronic heart failure. In heart failure, the heart is no longer able to supply the body with enough blood . Acute heart failure develops over a few hours to days. Causes are, for example, cardiac arrhythmia , cardiac tamponade, pulmonary embolism , cardiac valve insufficiency or myocardial infarction .

Chronic heart failure develops over a period of months to years. Causes are, for example, chronic lung diseases . Cardiac glycosides are also administered for atrial fibrillation or atrial flutter. Atrial fibrillation and atrial flutter can be completely asymptomatic. Those affected often only notice a drop in performance. However, symptoms such as dizziness , shortness of breath , feelings of anxiety or chest pain are also possible .

Risks & side effects

The use of cardiac glycosides and in particular the use of digoxin are controversial. Current studies show that patients with heart failure who were treated with digoxin had a 72 percent higher mortality rate than patients who were treated with other drugs.

Cardiac glycosides also have a fairly narrow therapeutic window. Even small deviations from the optimal dose can lead to undesirable effects and symptoms of poisoning. In many cases, the therapeutic and toxic areas overlap. Patients often complain of loss of appetite and nausea . Digitalis intoxication from overdose is manifested by vomiting , diarrhea and cardiac arrhythmias. Headaches , inner restlessness and even psychotic states of confusion can also occur.

Green-yellow vision is typical of digitalis intoxication. In addition, those affected see bluish stars or dots. These phenomena are called the cornflower phenomenon.

Intoxications are treated causally with an inhibition of the further absorption of the active substance. For this purpose, gastric lavage is performed. Alternatively, activated charcoal can also be administered. In addition, the circulation between the intestine and liver is interrupted by the administration of cholestyramine . Above all, the electrolyte disturbances are symptomatically balanced and the cardiac arrhythmia treated. There is also the option of administering a digitalis antidote. However, there is a risk of an allergic reaction, which can go as far as allergic shock .

It should be noted that the potency of cardiac glycosides can be affected by various medications and also by fluctuating concentrations of electrolytes in the blood. It must therefore always be used in an individual dosage. In addition, close blood controls are required when taking cardiac glycosides.

The cardiac glycoside digoxin must not be administered in renal failure . Digitoxin is contraindicated in combined renal and hepatic insufficiency.

Lisa Newlon
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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.