How often to check digoxin (digitalis glycoside) serum levels?

From the Guidelines

Digoxin serum levels should be checked 6-8 hours after the last dose in patients on oral therapy, or 12-24 hours after an IV dose, with monitoring occurring every 6-12 months for patients on maintenance therapy with stable renal function, and more frequently (every 1-3 months) for those with risk factors such as renal impairment, electrolyte disturbances, or interacting medications 1.

Key Considerations

• The therapeutic range for digoxin is typically 0.8-2.0 ng/mL, though lower targets (0.5-0.9 ng/mL) are often preferred for heart failure patients 1.
• Regular monitoring is essential because digoxin has a narrow therapeutic window, and factors like kidney function significantly affect its clearance, making toxicity a serious concern 1.
• Additional testing is warranted whenever there are changes in renal function, when starting or stopping interacting medications, or if signs of toxicity appear (nausea, vomiting, visual disturbances, or arrhythmias) 1.

Monitoring Frequency

• Patients with stable renal function: every 6-12 months 1.
• Patients with risk factors (renal impairment, electrolyte disturbances, interacting medications): every 1-3 months 1.
• Whenever changes in renal function, interacting medications, or signs of toxicity occur 1.

Important Interactions

• Medications that can increase serum digoxin concentrations and risk of toxicity: clarithromycin, erythromycin, amiodarone, itraconazole, cyclosporine, verapamil, quinidine 1.
• Conditions that can increase risk of toxicity: hypokalemia, hypomagnesemia, hypothyroidism 1.

From the FDA Drug Label

To allow adequate time for equilibration of digoxin between serum and tissue, sampling of serum concentrations should be done just before the next scheduled dose of the drug. If this is not possible, sampling should be done at least 6 to 8 hours after the last dose, regardless of the route of administration or the formulation used

The frequency of getting a digoxin serum level is not explicitly stated in the provided drug labels. However, it is recommended that sampling of serum concentrations should be done just before the next scheduled dose of the drug, or at least 6 to 8 hours after the last dose.

• Steady-state serum digoxin concentrations will be achieved in approximately five half-lives of the drug for the individual patient, which can take between 1 and 3 weeks depending on the patient's renal function.
• No specific frequency for checking serum levels is provided, but it is implied that it should be done as needed to assess the adequacy of digoxin therapy and to monitor for potential toxicity 2.

From the Research

Frequency of Digoxin Serum Level Measurement

The frequency of measuring digoxin serum levels is not explicitly stated in the provided studies. However, the studies suggest that:

• Serum digoxin concentrations should be monitored in patients receiving digoxin treatment, especially those with renal dysfunction and hypokalemia 3.
• The measurement of serum digoxin concentration (SDC) levels holds significance not only in the monitoring of toxicity but also in ensuring adherence to the recommended therapeutic range during therapy 4.
• Routine monitoring of SDC is common, but often does not lead to clinical action, such as dose adjustment or drug discontinuation 5.

Factors Affecting Digoxin Serum Levels

Several factors can affect digoxin serum levels, including:

• Renal function: Renal failure, elevated creatinine, and magnesium levels can significantly increase SDC levels 4.
• Drug interactions: Many medications, including quinidine, amiodarone, and verapamil, can alter digoxin pharmacokinetics and result in increased SDC levels 6.
• Electrolyte levels: Potassium, sodium, and calcium levels outside the normal limits can affect SDC levels 4.
• Age and gender: Age, male gender, and the presence of diabetes mellitus may be associated with greater SDC levels, although this was not statistically significant in one study 4.

Therapeutic Range and Toxicity

The therapeutic range of serum digoxin varies, but is generally considered to be between 0.5 and 2.0 ng/mL 6, 4, 5.

• SDC levels below 0.5 ng/mL may indicate subtherapeutic levels, while levels above 2.0 ng/mL may indicate toxicity 4, 5.
• The presence of renal failure, elevated creatinine, and low or high potassium values can increase the risk of toxicity 4.