What workup is needed to prescribe digoxin (Digitalis glycoside)?

From the Guidelines

Before prescribing digoxin, a thorough workup including a complete medical history, laboratory tests (serum electrolytes, renal function tests, liver function tests), a baseline ECG, and for patients with heart failure, an echocardiogram, is necessary to ensure safe and effective therapy. This comprehensive approach is crucial given the potential for toxicity and the need to optimize dosing, as highlighted in the 2022 AHA/ACC/HFSA guideline for the management of heart failure 1.

When considering digoxin therapy, it's essential to evaluate the patient's cardiac conditions, renal function, and medication use, as these factors can significantly impact the safety and efficacy of the treatment. Laboratory tests should include:

• Serum electrolytes (potassium, magnesium, calcium) to assess the risk of toxicity
• Renal function tests (BUN, creatinine, GFR) to determine the appropriate dose
• Liver function tests, as liver disease can affect digoxin metabolism A baseline ECG is necessary to assess heart rhythm and conduction, and for patients with heart failure, an echocardiogram is valuable to evaluate cardiac function and structure.

Additionally, thyroid function tests are important, as thyroid disorders can affect digoxin metabolism and response 1. A medication review is also crucial to identify potential drug interactions, especially with medications that can alter digoxin levels or increase toxicity risk. Body weight should be recorded, as digoxin dosing is weight-based. Once therapy begins, regular monitoring of digoxin serum levels is necessary, with the therapeutic range typically between 0.8-2.0 ng/mL, although recent guidelines suggest that levels should be kept below 1.2 ng/mL to minimize the risk of mortality 1.

This thorough workup helps prevent toxicity, which can manifest as nausea, visual disturbances, confusion, and dangerous cardiac arrhythmias, while ensuring the medication effectively treats the underlying condition. The initiation of digoxin should be at a low dose, typically 0.125 to 0.25 mg daily, with adjustments based on patient response and serum levels, and consideration of the patient's age, with lower doses (0.125 mg daily or every other day) recommended for patients over 70 years of age 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 maintenance dose should be based upon the percentage of the peak body stores lost each day through elimination.

% Daily Loss = 14 + Ccr/5 (Ccr is creatinine clearance, corrected to 70 kg body weight or 1.73 m body surface area.)

Table 5 provides average daily maintenance dose requirements of digoxin tablets for patients with heart failure based upon lean body weight and renal function:

If only serum creatinine concentrations (Scr) are available, a Ccr (corrected to 70 kg body weight) may be estimated in men as (140 - Age)/Scr. For women, this result should be multiplied by 0.85.

The workup needed to prescribe digoxin includes:

• Serum creatinine concentrations (Scr) to estimate creatinine clearance (Ccr)
• Lean body weight to determine the appropriate dose
• Assessment of renal function to adjust the dose accordingly
• Clinical evaluation to determine the need for digoxin and to monitor its effectiveness and potential toxicity 2
• Serum digoxin concentration measurements to monitor the patient's response to the drug and adjust the dose as needed 2

From the Research

Workup Needed to Prescribe Digoxin

To prescribe digoxin, the following workup is needed:

• Assessment of renal function, including serum creatinine concentration and estimated creatinine clearance 3, 4, 5, 6
• Evaluation of electrolyte levels, including potassium, sodium, and calcium 7
• Consideration of patient's age, weight, and presence of comorbidities, such as diabetes mellitus 7, 4
• Monitoring of serum digoxin concentrations to ensure therapeutic levels and minimize the risk of toxicity 3, 7, 5

Key Factors to Consider

Some key factors to consider when prescribing digoxin include:

• Renal function: impaired renal function can lead to elevated digoxin levels and increased risk of toxicity 3, 4, 5, 6
• Electrolyte levels: abnormal electrolyte levels, such as low potassium or high calcium, can increase the risk of digoxin toxicity 7
• Age and weight: elderly patients and those with low body weight may be at increased risk of digoxin toxicity 3, 4
• Presence of comorbidities: patients with comorbidities, such as diabetes mellitus, may be at increased risk of digoxin toxicity 7

Laboratory Tests

The following laboratory tests may be needed to monitor patients on digoxin therapy:

• Serum digoxin concentration: to ensure therapeutic levels and minimize the risk of toxicity 3, 7, 5
• Serum creatinine concentration: to assess renal function and estimate creatinine clearance 3, 4, 5, 6
• Electrolyte levels: to monitor for abnormal electrolyte levels that may increase the risk of digoxin toxicity 7
• Cystatin C: may be a more sensitive marker of renal function than serum creatinine 5