Digoxin Toxicity

Digitalis is a medication prescribed to certain heart patients. Digitalis toxicity is a complication of digitalis therapy, or it may be occur when someone takes more than a large amount of the drug at one time. (This is called an acute ingestion.)

The most common prescription form of this medication is called digoxin.

Digitoxin is another form of digitalis.




Causes

Digitalis toxicity can be caused by high levels of digitalis in the body, or a decreased tolerance to the drug. Patients with decreased tolerance may have "normal" digitalis levels in their blood.

Digitalis toxicity can occur from a single exposure or chronic overmedication, or it may occur in patients with normal blood levels of digitalis if other risks are present.

Factors predisposing to digitalis toxicity are advanced age, hypoxia,  hypokalaemia, hypomagnesaemia, hypercalcaemia, hypothyroidism, amyloidosis and renal failure. The most common precipitating factor is hypokalaemia. 

People with heart failure who take digoxin are commonly given medications called diuretics, which remove excess fluid from the body. Many diuretics can cause potassium loss. Low levels of potassium in the body increase the risk of digitalis toxicity. Digitalis toxicity may also result in persons who take the drug and who have low levels of magnesium in the body.

Risks include taking digitalis medications such as digoxin or digitoxin along with medications that interact with digitalis such as quinidine, verapamil, amiodarone, and others.

Reduced kidney function will cause digitalis to build up in the body rather than be removed normally through urine. Therefore, any disorders that disrupt kidney functioning (including dehydration) make digitalis toxicity more likely.



Symptoms


The earliest signs of digitalis toxicity include nausea, vomiting and anorexia.

Chronic toxicity causes exacerbation of heart failure, weight loss, gynaecomastia and yellow vision.


Symptoms of digoxin toxicity include:

• Confusion
• Irregular pulse
• Loss of appetite
• Nausea, vomiting, diarrhea
• Palpitations
• Visual changes (unusual)
• Blind spots in vision
• Blurred vision
• Changes in color perception
• Halos or rings of light around objects
• Seeing lights or bright spots

Additional symptoms that may be associated with digitalis toxicity include:

• Decreased consciousness
• Decreased urine output
• Difficulty breathing when lying down
• Excessive nighttime urination
• Overall swelling

Exams and Tests

The heart rate may be rapid or slow and may be irregular.

An ECG is done to check for irregular heart beats. Characteristic ECG changes include bradycardia (the most frequent vital sign abnormality in toxicity), a prolonged PR interval. An accelerated junctional rhythm or bidirectional ventricular tachycardia suggests digoxin toxicity until proven otherwise.

Digoxin toxicity can result in any abnormal cardiac rhythm except type-II second-degree atrioventricular (AV) block. The characteristic arrhythmia includes non-paroxysmal atrial tachycardia with varying block. The other common arrhythmias include first-degree heart block, Wenkebach (type-I second-degree block) and complete (third degree) heart block, ventricular ectopics and ventricular tachycardia (VT) (uni- and
bi-directional). Ventricular fibrillation (VF) can also rarely occur. Another unusual arrhythmia is atrial flutter.

Blood tests will be done to check:

    BUN and creatinine (which help reveal kidney function)
    Digoxin and digitoxin levels
    Potassium level
    Magnesium level

See also:

    Blood chemistry
    Digoxin - test
    Digitoxin - test




Treatment

In an emergency, assist breathing as needed (see CPR) and get professional medical help.

Arrhythmias are treated according to which arrhythmia develops.

If toxicity is due to a recent, acute single exposure, treatment may involve:

• Activated charcoal
• Tube through the mouth into the stomach to wash out the stomach (gastric lavage)

Digitoxin blood levels may be lowered with repeated doses of charcoal, given after gastric lavage.

Methods to cause vomiting are usually not performed because vomiting can worsen slow heart rhythms.

In severe cases, medications called digoxin-specific antibodies may be prescribed. Hemodialysis may be required to reduce the levels of digitalis in the body.


Outlook (Prognosis)

The outcome varies depending on the extent of toxicity and arrhythmias that develop.



Possible Complications

• Arrhythmias, which may be deadly
• Heart failure

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