What is the target serum digoxin level for a patient on digoxin?

Target Serum Digoxin Level

The target serum digoxin concentration should be maintained between 0.5-0.9 ng/mL for patients with heart failure, as concentrations above 1.0 ng/mL have not shown superior outcomes and may increase mortality risk. 1

Therapeutic Range by Indication

Heart Failure

• Target: 0.5-0.9 ng/mL is the optimal range for heart failure patients, representing a lower target than historically recommended 1
• The European Society of Cardiology specifies a therapeutic range of 0.6-1.2 ng/mL, which is lower than previously recommended 2
• Concentrations above 1.0 ng/mL provide no additional clinical benefit and may increase mortality risk 1

Atrial Fibrillation with Heart Failure

• The same therapeutic range of 0.5-0.9 ng/mL applies when digoxin is used for rate control in atrial fibrillation with concomitant heart failure 1
• Digoxin is typically used in combination with beta-blockers for rate control in this population 1

FDA-Approved Therapeutic Window

• The FDA label states that approximately two-thirds of adequately digitalized adults (without toxicity) have serum concentrations ranging from 0.8-2.0 ng/mL 3
• However, this broader range is outdated—contemporary guidelines favor the lower target of 0.5-0.9 ng/mL based on more recent evidence showing improved safety without loss of efficacy 1

Toxicity Threshold

• Overt digoxin toxicity is commonly associated with serum levels greater than 2.0 ng/mL 4
• However, toxicity can occur at lower levels, particularly in the presence of:
  • Hypokalemia 4, 5
  • Hypomagnesemia 4, 5
  • Hypothyroidism 4, 5
  • Renal dysfunction 4
  • Advanced age 4
• Approximately one-third of patients with clinical toxicity have concentrations below 2.0 ng/mL 3
• Toxicity can even occur when serum concentration is within the therapeutic range (0.5-1.2 ng/mL) if risk factors are present 4

Clinical Context for Interpretation

Serum digoxin concentrations should always be interpreted in the overall clinical context, and an isolated measurement should not be used alone as the basis for dose adjustments 3

Timing of Blood Sampling

• Sampling should be done just before the next scheduled dose to allow adequate time for equilibration between serum and tissue 3
• If this is not possible, sampling should be done at least 6-8 hours after the last dose 3
• On once-daily dosing, concentrations will be 10-25% lower when sampled at 24 hours versus 8 hours, depending on renal function 3

Factors Affecting Interpretation

• Serum digoxin concentration may decrease acutely during periods of exercise without any change in clinical efficacy due to increased binding to skeletal muscle 3
• Concomitant medications that increase digoxin levels (amiodarone, verapamil, quinidine, clarithromycin, erythromycin, itraconazole, cyclosporine, propafenone, dronedarone) require dose reduction and closer monitoring 4, 1

Monitoring Frequency

• Regular digoxin concentration measurements are not necessary for routine monitoring 2
• The European Society of Cardiology states there is no evidence that regular digoxin concentration measurements confer better outcomes 2
• Monitoring should be performed when:
  • Adding medications that may increase digoxin levels 1
  • Signs of toxicity appear 1
  • Renal function changes 1
  • Electrolyte abnormalities develop 1

Common Pitfall

The most critical pitfall is using the older therapeutic range of 0.8-2.0 ng/mL, which increases the risk of toxicity without providing additional benefit. Always target 0.5-0.9 ng/mL for heart failure patients 1, and remember that clinical response and toxicity symptoms matter more than the number itself 3.