What are the therapeutic levels of digoxin (digitalis), normal electrocardiogram (EKG) readings, and optimal potassium (K+), magnesium (Mg2+), and calcium (Ca2+) levels for a patient on digoxin therapy?

From the Guidelines

For patients on digoxin therapy, the therapeutic serum level should be maintained between 0.5-1.0 ng/mL to minimize toxicity risks, as suggested by the most recent and highest quality study 1.

Therapeutic Digoxin Level and EKG Readings

The therapeutic level of digoxin is crucial for effective treatment while minimizing the risk of toxicity.

• The therapeutic serum level of digoxin ranges from 0.5 to 1.0 ng/mL, with most clinicians targeting this range to minimize toxicity risks.
• Normal EKG findings in patients on digoxin typically include a heart rate of 60-100 beats per minute, PR interval of 120-200 milliseconds, QRS duration of 60-100 milliseconds, and QT interval of 350-440 milliseconds, though digoxin may cause characteristic "scooping" of the ST segment (digitalis effect) 1.

Electrolyte Management

Electrolyte management is crucial for patients on digoxin therapy, as certain electrolyte imbalances can increase the risk of digoxin toxicity.

• Potassium levels should be maintained between 4.0-5.0 mEq/L.
• Magnesium levels should be maintained between 1.7-2.2 mg/dL.
• Calcium levels should be maintained between 8.5-10.5 mg/dL. Hypokalemia, hypomagnesemia, and hypercalcemia can increase digoxin toxicity risk by enhancing binding to cardiac cells 1.

Monitoring and Toxicity Prevention

Regular monitoring of digoxin levels and electrolytes is essential, particularly when starting therapy, changing doses, or adding medications that might affect digoxin metabolism.

• Symptoms of toxicity include nausea, visual disturbances, confusion, and cardiac arrhythmias, which require immediate medical attention and possible digoxin level measurement 1. It is also important to note that the management of hyperkalemia during the use of mineralocorticoid receptor antagonists may need to be revised, with narrower ranges of acceptable potassium levels, especially in patients with concomitant chronic kidney disease and/or diabetes mellitus over 65 years of age 1.

From the FDA Drug Label

In patients with hypokalemia or hypomagnesemia, toxicity may occur despite serum digoxin concentrations below 2.0 ng/mL, because potassium or magnesium depletion sensitizes the myocardium to digoxin. The usual amount of digoxin tablets that a 70 kg patient requires to achieve 8 to 12 mcg/kg peak body stores is 750 to 1250 mcg (0.75 to 1.25 mg). Peak digoxin body stores of 8 to 12 mcg/kg should provide therapeutic effect with minimum risk of toxicity in most patients with heart failure and normal sinus rhythm. Serum digoxin concentration may decrease acutely during periods of exercise without any associated change in clinical efficacy due to increased binding of digoxin to skeletal muscle Steady-state serum digoxin concentrations will be achieved in approximately five half-lives of the drug for the individual patient The maintenance dose should be based upon the percentage of the peak body stores lost each day through elimination.

The therapeutic digoxin level is between 0.5 and 2.0 ng/mL. For EKG readings, there is no specific information provided in the drug label. It is desirable to maintain normal serum potassium and magnesium concentrations in patients being treated with digoxin, as deficiencies of these electrolytes may result in toxicity. Calcium levels should also be monitored, as hypercalcemia can predispose the patient to digitalis toxicity, while hypocalcemia can nullify the effects of digoxin. 2 2 2

From the Research

Therapeutic Digoxin Level

• The therapeutic level of digoxin is generally considered to be between 0.7-1.5 ng/mL (or 0.9-2.0 nMol/L) 3
• However, a study published in 2018 found that the optimal digoxin concentration serum (SCD) should equal 1-2ng/ml 4
• Another study published in 2003 noted that serial assessment of serum digoxin levels is unnecessary in most patients, and that there appears to be little relationship between serum digoxin concentration and the drug's therapeutic effects 5

EKG Readings

• There is no specific information provided in the studies about the normal EKG readings for a patient on digoxin therapy
• However, it is known that digoxin can cause various EKG changes, including atrioventricular block, junctional tachycardia, and ectopic atrial tachycardia 6

Potassium, Magnesium, and Calcium Levels

• Potassium levels should be within the normal range (3.5-5 mmol/L) to minimize the risk of digoxin toxicity 6
• Magnesium levels should also be within the normal range (0.65-1.25 mmol/L), as hypomagnesemia can precipitate digoxin-induced dysrhythmia 6
• Calcium levels should be within the normal range, although there is limited information provided in the studies about the optimal calcium levels for patients on digoxin therapy
• It is essential to note that digoxin toxicity can occur even with normal digoxin and potassium levels, especially if there are electrolyte or metabolic disturbances, such as hypomagnesemia 6