How should I give a digoxin loading dose and continuous intravenous infusion in an adult (e.g., 70‑kg) patient, including dosing, monitoring, and transition to oral therapy?

How to Infuse Digoxin: Loading Dose and Continuous IV Administration

Loading Dose Administration

For rapid digitalization in hemodynamically stable adults requiring urgent rate control, administer an initial IV bolus of 0.25–0.5 mg (250–500 mcg) over at least 5 minutes, followed by additional 0.25 mg doses at 6–8 hour intervals, up to a maximum total loading dose of 1.0 mg over 24 hours (equivalent to 8–12 mcg/kg ideal body weight). 1, 2

Dosing Strategy by Weight

• Calculate the total loading dose using ideal body weight (IBW): 8–12 mcg/kg IBW is the recommended range for adults and pediatric patients over 10 years. 1, 2
• Administer half the total loading dose initially, then one-quarter of the loading dose every 6–8 hours twice. 2
• Do not exceed 12 mcg/kg IBW, as doses above this threshold are associated with significantly higher rates of serum digoxin concentrations ≥1.2 ng/mL (50.6% vs. 30.0%), which correlate with increased mortality risk, without improving rate control efficacy. 3

Administration Technique

• Infuse each dose over at least 5 minutes to prevent systemic and coronary vasoconstriction; avoid bolus administration. 2
• Administer undiluted or dilute with a 4-fold or greater volume of Sterile Water for Injection, 0.9% Sodium Chloride, or 5% Dextrose; use immediately after dilution. 2
• Do not mix digoxin with other drugs in the same container or administer simultaneously in the same IV line. 2

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Continuous IV Infusion (Maintenance Dosing)

Digoxin is not typically given as a continuous infusion; instead, transition to once-daily IV or oral maintenance dosing after the loading phase. 2

Maintenance Dose Selection

• For adults under 70 years with normal renal function: 2.4–3.6 mcg/kg/day IV (typically 0.125–0.25 mg once daily). 2
• For patients ≥70 years, impaired renal function, or low lean body mass: 0.125 mg once daily or 0.0625 mg once daily. 4, 2
• Adjust dose based on creatinine clearance (see Table 3 in FDA label): for CrCl 30–59 mL/min, reduce dose by 25–50%; for CrCl 15–29 mL/min, reduce by 50–75%; for CrCl <15 mL/min, use 0.0625 mg daily or every other day. 4

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Monitoring During and After Loading

Immediate Monitoring

• Measure serum digoxin concentration (SDC) at least 6–8 hours after the last loading dose to allow equilibration between serum and tissue. 4, 5
• Target therapeutic range: 0.5–0.9 ng/mL for heart failure; 0.6–1.2 ng/mL for atrial fibrillation. 1, 4, 2
• Concentrations >1.0 ng/mL offer no additional benefit and increase mortality risk in heart failure patients. 4

Electrolyte and Renal Monitoring

• Check baseline and serial potassium and magnesium levels: maintain potassium 4.0–5.5 mEq/L and correct hypomagnesemia before and during digoxin therapy, as deficiencies potentiate toxicity even at therapeutic SDC. 1, 4, 5
• Assess renal function (creatinine clearance) before each subsequent dose during loading and regularly during maintenance. 4, 2
• Obtain baseline ECG to exclude second- or third-degree AV block or pre-excitation syndromes (absolute contraindications). 1, 4

Signs of Toxicity to Monitor

• Cardiac: ventricular ectopy, AV block, bradycardia, bidirectional ventricular tachycardia. 1, 5
• Gastrointestinal: anorexia, nausea, vomiting (often earliest sign). 1, 5
• Neurological: visual disturbances (yellow/blurred vision), confusion, disorientation. 1, 5
• Toxicity can occur at SDC <2 ng/mL if hypokalemia, hypomagnesemia, hypothyroidism, renal dysfunction, or interacting drugs are present. 1, 5

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Transition to Oral Therapy

Switch to oral digoxin once the patient is hemodynamically stable and able to tolerate oral intake; oral bioavailability is approximately 70–80% of IV dosing. 6

Conversion Calculation

• An oral tablet of 0.5 mg has approximately the same bioavailability as 0.35–0.4 mg IV. 6
• For most patients, transition from IV to oral at the same daily dose (e.g., 0.125 mg IV daily → 0.125 mg PO daily), as the difference in bioavailability is clinically insignificant at maintenance doses. 2, 6
• Recheck SDC 1–2 weeks after transition to confirm therapeutic levels. 4

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Special Populations and Precautions

Elderly Patients (≥70 Years)

• Never exceed 0.125 mg daily in patients ≥75 years, even with normal renal function; higher doses increase toxicity without improving outcomes. 4
• Age-related renal decline mandates lower dosing even when serum creatinine appears normal; use Cockcroft-Gault equation adjusted for lean body weight. 4

Renal Impairment

• For CrCl <30 mL/min: start with 0.0625 mg daily or every other day; avoid loading doses unless absolutely necessary. 4, 2
• In dialysis-dependent patients: a loading dose of 10 mcg/kg IV is appropriate, but expect reduced volume of distribution (approximately one-third lower than normal). 7

Drug Interactions Requiring Dose Reduction

• Reduce digoxin dose by 30–50% when co-administered with amiodarone, verapamil, clarithromycin, erythromycin, itraconazole, cyclosporine, or propafenone. 1, 4
• Reduce dose by at least 50% with dronedarone. 1, 4
• Monitor SDC closely when adding any P-glycoprotein inhibitor or CYP3A4 inhibitor. 1, 4

Contraindications

• Absolute: second- or third-degree AV block without a permanent pacemaker; pre-excitation syndromes (WPW) with atrial fibrillation; previous digoxin intolerance. 1, 4
• Relative (use with extreme caution): decompensated heart failure with hypotension, cardiogenic shock, uncorrected hypokalemia or hypomagnesemia, hypothyroidism, acute myocardial infarction. 1, 4

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Common Pitfalls to Avoid

• Do not use loading doses in stable outpatients with chronic heart failure or atrial fibrillation; start directly with maintenance dosing. 4
• Do not administer digoxin to patients with hypokalemia (K <3.5 mEq/L) without first correcting potassium to ≥4.0 mEq/L. 4, 5
• Do not exceed 0.25 mg daily in most patients; higher doses (0.375–0.5 mg) are rarely needed and increase toxicity risk. 4, 8
• Do not rely on SDC alone to guide therapy; clinical response (symptom control, heart rate) is more important than achieving a specific serum level. 4, 8
• Do not use digoxin monotherapy for rate control in atrial fibrillation during exercise; combine with a beta-blocker for optimal efficacy. 1, 4