Cardiac Glycosides Poisoning - Mechanism and Side Effects

What Are Cardiac Glycosides?

Cardiac glycoside is a chemical used as medication and affects the body's heart, stomach, intestines, and nervous systems. It is most commonly used as the main ingredient to treat different heart medicines. Cardiac glycosides constitute a diverse family of naturally derived compounds widely known for their ability to bind to and inhibit the sodium pump.

Sir William Withering described the use of the foxglove plant, Digitalis purpurea, for the treatment of heart failure in 1985. More than 200 years later, cardiac glycosides are still prescribed for patients with atrial fibrillation, heart failure, or left ventricular dysfunction.

What Is the Mechanism of Cardiac Glycosides?

Cardiac glycoside is a chemical used mainly for heart failure and irregular heartbeat. It works on the mechanism of action that involves inhibiting the Na+ K+ ATPase enzyme, also known as the sodium-potassium pump. This results in the building up of sodium within the heart cells, decreasing the ability of the sodium-calcium exchanger to push calcium out of the cells, consequently causing calcium to build up in the sarcoplasmic reticulum. This leads to increased force of contraction (positive inotropic effect) which in turn has the effect of increasing the force of the heart’s contractions. The increase of intracellular calcium ions also raises the cell's resting membrane potential, leading to increased rates of spontaneous cellular depolarization and automaticity. The myocardium becomes painful and arrhythmogenic. In addition, increased vagal tone leads to bradycardia. Inhibition of the Na+ K+ ATPase also leads to hyperkalemia. Acute cardiac glycoside poisoning has a relation with hyperkalemia.

What Are the Side Effects Associated With Cardiac Glycosides?

Cardiac glycosides can have some evident side effects and can also cause poisoning and toxicity. The common adverse effects of cardiac glycosides include excessive tiredness and fatigue, anxiety, and hallucinations. In addition, symptoms of toxicity can include visual disturbances, nausea or vomiting, and cardiac arrhythmias.

In addition, high doses of cardiac glycosides can result in electrolyte imbalances involving sodium, potassium, calcium, and magnesium. Moreover, concurrently using certain medications can increase digoxin levels in the blood. These medications include nonsteroidal anti-inflammatory drugs (NSAIDs), calcium channel blockers, diuretics, Amiodarone, Cyclosporine, Amiodarone, and Quinidine. Finally, decreased renal function can also increase serum digoxin levels, as Digoxin is primarily excreted through the kidneys.

Side effects can often be controlled by reducing the dosage of Digoxin. Moreover, people who have cardiac arrhythmias should be monitored with blood tests for serum levels of Digoxin and electrolytes, together with an electrocardiogram to examine the heart and detect the defect in the heartbeat. In severe toxicity cases, administering Digoxin may be helpful in reducing serum digoxin levels rapidly.

What Are the Effects of Cardiac Glycosides on the Heart Rate?

At low therapeutic doses, cardiac glycosides can reduce heart rate and increase gastrointestinal activity for individuals, as they act on the parasympathetic nervous system. One part of the central nervous system responsible for relaxing our bodies and conserving energy is the parasympathetic nervous system. It is observed that 60 to 85 percent of pharmaceutical Digoxin is absorbed by ingestion, and it starts showing its effects within six to 12 hours post-ingestion.

In the case of an overdose, cardiac toxicity may start showing its toxicity within 30 minutes of intake. If the dose of cardiac glycosides is more than 2 mg (milligram) results in an overdose.

Why Are Cardiac Glycosides Still Used?

Cardiac glycosides are still in use. However, they can result in severe life-threatening side effects and toxicity, so they have been replaced with other kinds of medications as first-line treatment and choice of drug. For example, ACE inhibitors and beta-blockers. Cardiac glycosides are mostly contraindicated in ventricular fibrillation.

What Are the Other Important Facts Related to Cardiac Glycosides?

Cardiac glycosides belong to a group of drugs used as medications that inhibit the Na+ K+ ATPase enzyme, increasing the pressure or force of heart contractions. Digoxin is the most commonly prescribed cardiac glycoside, which can help in the treatment of atrial fibrillation, atrial flutter, and congestive heart failure. However, cardiac glycosides can cause severe side effects and toxicity, which are contraindicated in many hearts or other internal organ-related problems.

Why Patient Teaching And Education Is Important?

The patient should be well aware and properly instructed to follow the prescribed medications and dosing regimen and take medications simultaneously daily according to their signs and symptoms. The patient should not miss or double up the medication doses. Additionally, the patient should consult the healthcare provider if they experience any side effects.

Patients should get the correct education regarding pulse rate monitoring and report any pulse rate less than 60 and should be able to use the medical equipment for self-testing. In some cases, if digoxin toxicity is experienced by the patient, they should seek medical help immediately from the healthcare provider. The medication should be stored in space and dry in its original container, and do not mix it with other medications.

It is recommended to teach the patient about the use and intake of cardiac glycosides. The excessive use of cardiac glycoside can lead to serious life-threatening conditions.

Conclusion

Cardiac glycosides are commonly used drugs for the treatment of heart-related problems. It works on the mechanism of NA+ K+ ATPase. The administration of cardiac glycosides is associated with very serious life-threatening conditions. It can be treated with other medications like activated charcoal, Atropine, Beta-adrenoceptor agonists, temporary pacing, Anti-Digoxin Fab, magnesium, and some more agents under evaluation, including fructose-1,6-diphosphate and Anticalin are used. Patients taking cardiac glycoside should be aware of the use of the drug, and any side effects caused by the drug should be reported to their healthcare provider.