Digoxin (Lanoxin®)
| Drug Overview |  |
|---|---|
| Drug Class | Cardiac Glycoside |
| Subclass | Na⁺/K⁺ ATPase Inhibitor |
| Primary Uses | HFrEF; Atrial Fibrillation |
| Route | Oral / IV |
| Onset (IV) | 5–30 minutes |
| Half-life | ~36–48 hours (normal renal function) |
| Metabolism | Minimal hepatic |
| Elimination | Renal |
| Renal Adjustment | Yes |
| Hepatic Adjustment | No |
| Therapeutic Level | 0.5–0.9 ng/mL (HF) |
| Black Box Warning | No |
Overview
Digoxin is a cardiac glycoside that increases inotropy and enhances vagal tone.
It is used in:
- HFrEF (symptom improvement only — no mortality benefit)
- Atrial Fibrillation (rate control)
It is NOT first-line therapy in modern heart failure but remains useful in select patients.
Mechanism of Action
Primary Target:
- Inhibits Na⁺/K⁺ ATPase pump in cardiac myocytes
Cellular Effect:
- ↑ intracellular Na⁺
- ↓ Na⁺/Ca²⁺ exchanger activity
- ↑ intracellular Ca²⁺
Result:
- ↑ Contractility (positive inotropy)
Autonomic Effect:
- ↑ Vagal tone
- ↓ AV nodal conduction
- ↑ AV nodal refractory period
Net Effects:
- Improves systolic function
- Slows ventricular response in AF
Indications
Cardiovascular:
- HFrEF (symptom reduction)
- Atrial Fibrillation (rate control)
Not used for:
- Acute decompensated HF
- Mortality reduction
See also:
Dosing
Heart Failure (maintenance):
- 0.125–0.25 mg daily
Atrial Fibrillation:
- Similar dosing
- Lower doses preferred in elderly
Renal dosing:
- Reduce dose in CKD
- Monitor levels carefully
Target serum concentration:
- 0.5–0.9 ng/mL (HF)
- Avoid > 2.0 ng/mL
Contraindications
Absolute:
Relative:
- Severe hypokalemia
- Severe renal dysfunction
Adverse Effects
Common:
- Nausea
- Vomiting
- Anorexia
- Fatigue
Cardiac:
- Bradycardia
- AV block
- Ventricular arrhythmias
Visual:
- Yellow vision (xanthopsia)
- Blurred vision
Toxicity Risk Increases With:
- Hypokalemia
- Hypomagnesemia
- Hypercalcemia
- Renal dysfunction
Digoxin Toxicity
Mechanism:
- Excess intracellular calcium
- Increased automaticity
- Delayed afterdepolarizations
ECG Findings:
- Scooped ST segments (“dig effect”)
- AV block
- Ventricular ectopy
Treatment:
- Correct electrolytes
- Stop drug
See:
Drug Interactions
Increase Digoxin Levels:
- Macrolides
- Verapamil
Electrolyte-mediated Risk:
- Loop Diuretics → hypokalemia
- Thiazides → hypokalemia
Additive AV Nodal Suppression:
Monitoring
- Serum digoxin level
- Renal function
- Potassium
- ECG
Monitor especially in:
- Elderly
- CKD
- Patients on interacting drugs
Comparison Within Heart Failure Therapy
Unlike:
Digoxin:
- Does NOT reduce mortality
- Improves symptoms only
- Useful in HFrEF with AF
Clinical Pearls
- Narrow therapeutic window.
- Renally cleared — dose carefully.
- Hypokalemia dramatically increases toxicity risk.
- Yellow vision is classic but uncommon.
- Think of digoxin when AF + HFrEF coexist.