digoxin
Brand: Lanoxin
ISMP High Alert Beers Criteria TDM Required Prototype Drug
Drug Class: cardiac glycoside
Drug Family: cardiac glycoside
Subclass: Na+/K+-ATPase inhibitor
Organ Systems: cardiovascular
Mechanism of Action
Inhibits Na+/K+-ATPase pump causing intracellular Na+ accumulation leading to increased intracellular Ca2+ via Na+/Ca2+ exchanger; increases myocardial contractility; increases vagal tone slowing AV conduction.
Na+/K+-ATPase (cardiac)vagal tone (indirect)
Indications
- heart failure (HFrEF — symptom control)
- atrial fibrillation/flutter (rate control)
Contraindications
- ventricular fibrillation
- pre-excitation syndromes (WPW)
- second/third degree AV block without pacemaker
- hypertrophic obstructive cardiomyopathy
- hypokalemia (increases toxicity risk)
Adverse Effects
Common
- bradycardia
- nausea/vomiting/anorexia
- visual disturbances (yellow-green halos)
- PR prolongation
Serious
- life-threatening arrhythmias (VT, VF, complete AV block)
- digoxin toxicity (narrow therapeutic index)
Pharmacokinetics (ADME)
| Absorption | 70-80% oral tablets; 90-100% capsule/liquid |
| Distribution | large Vd; distributes to skeletal muscle |
| Metabolism | minimal hepatic |
| Excretion | renal 50-70% unchanged |
| Half-life | 38-48 hours |
| Onset | 1-3 hours |
| Peak | 6-8 hours |
| Duration | 24-48 hours (steady state) |
| Protein Binding | 25% |
| Vd | 6-8 L/kg |
Drug Interactions
| Drug / Agent | Mechanism | Severity |
|---|---|---|
| amiodarone | increases digoxin level by 70-100% (reduce digoxin dose 50%) | major |
| verapamil | increases digoxin level (P-gp inhibition) | major |
| hypokalemia (diuretics) | decreases digoxin binding to Na/K ATPase — toxicity at normal levels | major |
| quinidine | increases digoxin level (P-gp inhibition, volume of distribution decrease) | major |
Nursing Considerations
- Narrow therapeutic index: target level 0.5-0.9 ng/mL in HF (higher levels → toxicity without added benefit)
- Draw trough level 6-12 hours after dose
- Monitor K+, Mg2+, Ca2+ — hypokalemia and hypomagnesemia precipitate toxicity
- Digibind (digoxin immune Fab) for toxicity reversal
- Check apical pulse 1 min — hold if <60 bpm; teach patient self-monitoring
Clinical Pearls
- DIG trial: digoxin reduces HF hospitalizations but NOT mortality
- Target serum level 0.5-0.9 ng/mL — higher levels NOT more effective and increase mortality
- Volume of distribution: large (6-8 L/kg) — loading dose needed; distributed to skeletal muscle (falsely elevated levels immediately after dose)
- Digoxin toxicity triad: GI symptoms (nausea, vomiting, anorexia), cardiac arrhythmias, CNS/visual (yellow-green halos, scotomas)
Safety Profile
Pregnancy use-with-caution
Lactation use-with-caution
Renal Adjustment Required
Hepatic Adjustment Not required
TDM Required
Concordance Terms
Cross-referenced clinical concepts — click any term to see all content where it appears.