In an adult with atrial fibrillation and rapid ventricular response who cannot use beta‑blockers or non‑dihydropyridine calcium‑channel blockers, what is the appropriate digoxin loading and maintenance dosing, including adjustments for age >75 years, weight <60 kg, or impaired renal function, and recommended serum level monitoring?

Digoxin Dosing for Atrial Fibrillation with Rapid Ventricular Response

When Digoxin is Appropriate

Digoxin is a Class I recommended agent for acute rate control in atrial fibrillation with rapid ventricular response when beta-blockers and non-dihydropyridine calcium channel blockers are contraindicated, particularly in patients with heart failure. 1, 2

• Digoxin should be used as an adjunctive agent, not first-line monotherapy, because it is generally ineffective at controlling ventricular rate during exercise or acute situations when used alone 3, 4
• Beta-blockers are superior to digoxin for rate control, especially during exertion, but when these are contraindicated digoxin becomes a primary option 5, 6
• Intravenous digoxin is specifically recommended for acute rate control in patients with heart failure and no accessory pathway 2

Loading Dose Regimen

For adults requiring rapid rate control, administer 0.5 mg intravenous bolus, with a total loading dose of 0.75–1.5 mg over 24 hours in divided doses. 1, 7

Administration technique:

• Give half the total loading dose initially, then ¼ of the loading dose every 6–8 hours twice 7
• Administer each dose over 5 minutes or longer to prevent systemic and coronary vasoconstriction; avoid bolus administration 7
• No more than 500 mcg should be injected into a single intramuscular site if IV access is unavailable, though IV is strongly preferred 7

Important caveat:

• Loading doses are unnecessary and should be avoided when initiating chronic heart failure therapy in stable outpatients 5, 8
• Loading is reserved for acute situations requiring rapid rate control 7

Maintenance Dose

The standard maintenance dose is 0.125–0.25 mg daily for most adults with normal renal function. 1, 5, 8

Dose adjustments for vulnerable populations:

Age >75 years:

• Reduce to 0.125 mg daily or every other day 5
• Patients over 70 years require lower dosing due to reduced lean body mass and declining renal function 8

Weight <60 kg (low lean body mass):

• Use 0.125 mg daily 5, 8
• Lower lean body mass increases risk of toxicity at standard doses 8

Impaired renal function:

• Reduce dose to 0.125 mg daily or every other day depending on creatinine clearance 5
• Check renal function before starting and adapt dose in patients with chronic kidney disease 1
• The FDA label provides weight and renal function-based dosing tables for precise adjustment 7

Dosing algorithm:

• Normal renal function, age <70, weight >60 kg: 0.125–0.25 mg daily 1, 5
• Any of: age >70, weight <60 kg, or renal impairment: 0.125 mg daily 5, 8
• Severe renal impairment or multiple risk factors: 0.125 mg every other day 5

Serum Level Monitoring

Target serum digoxin concentration is 0.5–0.9 ng/mL; levels above 1.0 ng/mL offer no additional benefit and may increase mortality risk. 5

Monitoring strategy:

• Serial assessment of serum digoxin levels is unnecessary in most stable patients 8
• Check levels when toxicity is suspected or when drug interactions are introduced 8
• Digoxin toxicity commonly occurs with levels >2 ng/mL but can occur at lower levels if hypokalemia, hypomagnesemia, or hypothyroidism coexist 1, 8
• High plasma levels are associated with increased risk of death 1

Critical Contraindications and Precautions

Absolute contraindications:

• Significant sinus node dysfunction or second/third-degree AV block without a permanent pacemaker 5, 8
• Pre-excitation syndromes (Wolff-Parkinson-White) with atrial fibrillation—use procainamide instead 3

Use with extreme caution when:

• Combining with other AV-nodal blocking agents (amiodarone, beta-blockers, calcium channel blockers)—close monitoring required 5, 8
• Hypokalemia, hypomagnesemia, or hypothyroidism present—these markedly increase toxicity risk even at therapeutic levels 5, 8
• Concomitant medications that increase digoxin levels: quinidine, verapamil, spironolactone, flecainide, amiodarone 8

Combination Therapy

A combination of digoxin plus beta-blocker (when tolerated) is reasonable (Class IIa) to control both resting and exercise heart rate. 1, 5

• Digoxin monotherapy is ineffective for exercise rate control but combination therapy controls rate at rest and during activity 4, 9
• When amiodarone is added for additional rate control, reduce the digoxin dose 8
• Avoid non-dihydropyridine calcium channel blockers (verapamil, diltiazem) if heart failure with reduced ejection fraction or decompensation is present 2

Common Pitfalls to Avoid

• Do not use digoxin as monotherapy for acute rate control—it is generally inefficacious alone in acute AF with RVR 3
• Do not administer loading doses for chronic stable heart failure—reserve loading for acute situations only 5, 8
• Do not target high serum levels—there is little relationship between serum concentration and therapeutic effect, but clear relationship with toxicity 8
• Do not use high doses (>0.25 mg daily) for rate control—higher doses rarely provide benefit and increase toxicity risk 8
• Always check electrolytes and renal function before initiating—hypokalemia and renal impairment are the most common precipitants of toxicity 1, 8