What is Digoxin Toxicity?
Digoxin, a medicine derived from the foxglove plant, was historically used for treating swelling or ‘dropsy’ caused by excess body fluid. Today it’s primarily used to enhance the functioning of a failing heart, particularly in people with congestive heart failure. It improves heart muscle’s efficiency but doesn’t extend the patient’s life. Its usage is limited due to its narrow range of safe and effective dosage.
An overdose of digoxin, whether intentional or accidental, can lead to digoxin toxicity that can present either immediately or over a long period, particularly if kidney function deteriorates in patients taking this medicine. Furthermore, exposure to certain plants or animals that contain substances similar to digoxin, like oleander, red squill, or toad species named Bufo, can produce similar toxic effects.
What Causes Digoxin Toxicity?
Digoxin works and also causes its side effects by interfering with the sodium-potassium pump in our cells. This results in a rise in sodium levels inside cells, which in turn causes a rise in calcium levels because less calcium can be kicked out of the cell through its usual exit route. Having more calcium in the cell can improve the strength of the heart’s contractions, which can be helpful in managing symptoms of congestive heart failure (CHF).
However, if the digoxin levels are too high, it can also speed up the heart’s automatic rhythm, which might be harmful. Digoxin also increases the activity of the vagus nerve, which slows down the speed at which electrical signals pass through a part of heart called the AV node. This effect can be beneficial in controlling fast and irregular heart rhythms from the upper chambers of the heart, also known as atrial tachydysrhythmias.
Risk Factors and Frequency for Digoxin Toxicity
About 1% of heart failure patients who receive digoxin treatment encounter toxicity issues. Furthermore, digoxin toxicity accounts for 1% of the adverse drug effects in patients over the age of 40. This toxicity incidence increases to more than 3% in patients above the age of 85. Looking at pediatric exposure, we find that 80% is due to plant ingestions, and the remaining 20% is attributed to medication ingestion. In terms of dysrhythmias, which are abnormal heart rhythms, ventricular ones are more frequent in older adults, while, in children, supraventricular dysrhythmias are more prevalent.
Signs and Symptoms of Digoxin Toxicity
Digoxin toxicity is a condition that can cause a range of symptoms, the most common of which is an upset stomach. An individual may also experience vision changes, including seeing a yellow-green color, along with heart-related symptoms like heart palpitations, shortness of breath, and fainting. Older adults might only have nonspecific symptoms like dizziness and tiredness. Knowing when the last dose of the medication was taken is crucial in evaluating the level of digoxin in the body.
- Upset stomach
- Vision changes (seeing a yellow-green color)
- Heart palpitations
- Shortness of breath
- Fainting
- Dizziness (common in older adults)
- Fatigue (common in older adults)
Testing for Digoxin Toxicity
When dealing with acute digoxin toxicity, certain tests need to be conducted immediately. These tests include an electrocardiogram (ECG), a basic metabolic panel, and a check of digoxin levels. It’s important to do these tests again six hours after the person has ingested the substance. The ECG may show specific changes such as a scooping pattern on the ST segments, but this isn’t necessarily a sign of toxicity as it can also appear at therapeutic levels of digoxin.
The most common abnormality seen on the ECG is the frequent occurrence of premature ventricular contractions (PVCs). However, a specific ECG change – bidirectional ventricular tachycardia (rapid heart rate) – is a key sign of digoxin toxicity, but it can also appear in other types of poisonings, like the one caused by aconitine.
In cases of acute overdose, checking for acetaminophen and aspirin levels can help detect a hidden overdose.
For chronic toxicity, it’s essential to find what’s causing it. Some common causes are infection, kidney failure, or accidental overdose. It’s important to note that the levels of digoxin in the bloodstream don’t always correspond to the severity of toxicity. This is because digoxin levels can vary across different tissues and be affected by other factors contributing to its toxic effects.
Treatment Options for Digoxin Toxicity
Digoxin-specific antibody antigen-binding fragments, also known as DSFab, can treat the harmful effects of digoxin, a heart medication.
DSFab may be prescribed when digoxin causes serious health issues, including:
* Abnormal heart rhythms
* High-grade blocking of the heart’s electrical signals
* Low blood pressure
* Slowed heart rate that causes symptoms
* High potassium levels in cases of digoxin overdose
* In cases where an adult has ingested more than 10 mg or a child has ingested more than 4 mg of digoxin
* When digoxin levels in the blood are too high.
The dosage of DSFab depends on the severity of the situation. In life-threatening cases following a digoxin overdose, 10 to 20 vials might be given. For long-term digoxin effects in adults, three to six vials are recommended, whereas children should receive one to two vials.
Methods for calculating the right dose include:
* Acute overdose: Number of vials = 0.8 times the digoxin dose divided by 0.5
* Acute or long-term effects: Number of vials = (steady state digoxin level times weight in kg) divided by 100
DSFab can also be used to treat poisoning from natural toxins, but how much to administer isn’t clearly defined.
Usually, DSFab is given as a 30-minute infusion, but in critical situations, it can be given all at once. The effects start around 20 minutes after administration and are usually fully realized after approximately 90 minutes.
It’s important to avoid fully reversing digoxin effects in patients who regularly take digoxin, as it might worsen their underlying heart disease. Such patients should be closely watched after treatment.
If DSFab is not available, other treatments, including activated charcoal, atropine, and anti-arrhythmic drugs like phenytoin or lidocaine, can be used. In some cases, electrical stimulation or pacing of the heart may be necessary. Dialysis can be useful in cases of acute kidney failure or severe high potassium levels, but it doesn’t effectively treat digoxin toxicity.
Finally, how patients are managed after treatment depends on their symptoms, stability, as well as their potassium and digoxin levels.
What else can Digoxin Toxicity be?
The term ‘bidirectional ventricular tachycardia’ refers to a specific kind of abnormal heart rhythm. It has traditionally been associated with a harmful level of digoxin, a heart medication. However, this irregular heartbeat can also occur as a result of poisoning from plants like wolfsbane or monkshood (also known as aconitine poisoning). Additionally, it can happen in people who have an inherited condition called familial catecholaminergic polymorphic ventricular tachycardia (CPVT).
