Lanoxin (digoxin) Dosing, Indications, Interactions, Adverse Effects ...

Dosage Forms & Strengths

oral solution

• 0.05mg/mL

injectable solution

• 0.1mg/mL
• 0.25mg/mL

tablet

• 0.0625mg (Lanoxin only)
• 0.125mg
• 0.1875mg (Lanoxin only)
• 0.25mg

Atrial Fibrillation

Rapid digitalizing (loading-dose) regimen

• IV: 8-12 mcg/kg (0.008-0.012 mg/kg) total loading dose; administer 50% initially; then may cautiously give 1/4 the loading dose q6-8hr twice; perform careful assessment of clinical response and toxicity before each dose
• PO: 10-15 mcg/kg total loading dose; administer 50% initially; then may cautiously give 1/4 the loading dose q6-8hr twice; perform careful assessment of clinical response and toxicity before each dose

Maintenance

• PO: 3.4-5.1 mcg/kg/day or 0.125-0.5 mg/day PO; may increase dose every 2 weeks based on clinical response, serum drug levels, and toxicity
• IV/IM: 0.1-0.4 mg/day; IM route not preferred due to severe injection site reaction

Heart Failure

As per ACCF/AHA guidelines, a loading dose to initiate digoxin therapy in patients with heart failure is not necessary

0.125-0.25 mg/day PO/IV; higher doses including 0.375-0.5 mg/day rarely needed

Use lower end of dosing (0.125 mg/day) in patients with impaired renal function or low lean body mass

Dosage Modifications

Adjust maintenance dose by estimating CrCl and measuring serum levels

In heart failure, higher dosages have no additional benefit and may increase toxicity; decreased renal clearance may lead to increased toxicity

In geriatric patients, use lean body weight to calculate dose

Dosing Considerations

Monitoring to assess safety, efficacy, and therapeutic blood levels

• Monitor for signs and symptoms of digoxin toxicity and clinical response
• Adjust dose based on toxicity, efficacy, and blood levels
• Very narrow margin between effective therapeutic and toxic dosages
• Serum digoxin levels 2 ng/mL have been associated with increased toxicity without increased benefit
• Interpret serum digoxin concentration in overall clinical context, and do not use an isolated measurement of serum digoxin concentration as basis for increasing or decreasing dose
• Serum digoxin concentrations may be falsely elevated by endogenous digoxin-like substances (eg, spironolactone); if assay is sensitive to interfering substances, consider obtaining a baseline digoxin level before initiating and correct post-treatment values by the reported baseline level
• Obtain serum digoxin concentrations just before next scheduled dose or at least 6 hr after last dose
• Digoxin concentration is likely to be 10-25% lower when sampled right before next dose (24 hr after dosing) compared to sampling 8 hr after dosing (using once-daily dosing) However, there will be only minor differences in digoxin concentrations using twice daily dosing whether sampling is done at 8 or 12 hr after a dose

Switching from IV to oral or between brands/generics

• When switching from IV to oral digoxin formulations, make allowances for differences in bioavailability when calculating maintenance dosages
• Tablets are 60-80% bioavailable, whereas IV solution is 100% bioavailable
• Avoid switching between different PO forms or between brand and generic forms of digoxin; bioavailability varies

ECG changes

• Therapeutic doses may cause prolongation of PR interval and depression of ST segment on ECG
• May produce false positive ST-T changes on ECG during exercise testing
• These electrophysiologic effects are not indicative of toxicity
• Does not significantly reduce heart rate during exercise