Digoxin is one of the oldest and most examined cardiac drugs. Despite newer therapies, it still holds an important place in heart failure and atrial fibrillation, and is a classic high-yield topic in pharmacology, medicine, cardiology, and emergency care.
What Is Digoxin?
Digoxin is a cardiac glycoside derived from the Digitalis plant. It improves cardiac contractility and controls heart rate, especially in atrial fibrillation.
Quick Drug Profile
| Feature | Details |
|---|---|
| Drug class | Cardiac glycoside |
| Source | Digitalis lanata |
| Main actions | ↑ Contractility, ↓ Heart rate |
| Therapeutic index | Narrow |
| Routes | Oral, IV |
| Monitoring | Required |
Why Digoxin Is Clinically Important
Digoxin uniquely provides:
1. Positive inotropic effect (stronger contraction)This combination makes it especially useful in heart failure with atrial fibrillation.
Mechanism of Action (Very High-Yield)
Digoxin works by inhibiting the Na⁺/K⁺-ATPase pump in cardiac myocytes.
Step-by-Step Mechanism
1. Digoxin inhibits Na⁺/K⁺-ATPaseVagal Effect
- Increases vagal tone
- Slows AV node conduction
- Decreases heart rate
One-Line Exam Answer
Digoxin increases intracellular calcium by inhibiting Na⁺/K⁺-ATPase
Pharmacological Effects of Digoxin
On the Heart
- ↑ Force of contraction
- ↓ Heart rate
- ↓ AV conduction
On ECG
- Shortened QT interval
- Scooped ST segment (“reverse tick” sign)
- Prolonged PR interval
Clinical Uses of Digoxin
1. Heart Failure (HFrEF)
- Improves symptoms
- Reduces hospitalizations
- Does not reduce mortality
Best used in systolic heart failure.
2. Atrial Fibrillation (Rate Control)
- Especially useful when heart failure is present
- Controls ventricular rate by slowing AV conduction
3. Atrial Flutter (Selected Cases)
When Digoxin Is NOT Preferred
- Acute heart failure
- Diastolic heart failure
- Wolff-Parkinson-White syndrome
- Ventricular arrhythmias
Pharmacokinetics (Simplified)
| Parameter | Details |
|---|---|
| Absorption | Oral (good) |
| Protein binding | Low |
| Distribution | Large (heart, kidney) |
| Elimination | Renal |
| Half-life | ~36 hours |
Dose adjustment required in renal failure.
Therapeutic Drug Monitoring (Very Important)
| Parameter | Value |
|---|---|
| Therapeutic level | 0.5–2.0 ng/mL |
| Toxic level | >2.0 ng/mL |
Digoxin has a narrow therapeutic index.
Digoxin Toxicity (Extremely High-Yield)
Causes
- Overdose
- Renal failure
- Hypokalemia
- Drug interactions (amiodarone, verapamil)
Symptoms of Digoxin Toxicity
Gastrointestinal
- Nausea
- Vomiting
- Abdominal pain
Neurological
- Confusion
- Delirium
- Visual disturbances
Classical sign: Yellow-green vision (xanthopsia)
Cardiac (Most Dangerous)
- Bradycardia
- AV block
- Ventricular arrhythmias
ECG Changes in Digoxin Toxicity
- Ventricular premature beats
- Atrial tachycardia with block
- Bidirectional ventricular tachycardia (classic)
Management of Digoxin Toxicity
Immediate Steps
- Stop digoxin
- Correct electrolytes (especially potassium)
Antidote
Digoxin-specific antibody fragments (Digoxin Fab)Important Drug Interactions
Drugs that increase digoxin levels:
- Amiodarone
- Verapamil
- Quinidine
- Erythromycin
Electrolyte interaction:
1. Hypokalemia ↑ toxicityDigoxin vs Other Heart Failure Drugs
| Feature | Digoxin | Beta-blockers / ACE inhibitors |
|---|---|---|
| Symptom relief | Yes | Yes |
| Mortality benefit | No | Yes |
| Heart rate control | Yes | Variable |
| Toxicity risk | High | Lower |
Exam-Oriented Memory Tricks
Mechanism
“Na⁺ out → Ca²⁺ in → Heart wins”
Toxicity
“DIG TOX”
- Diarrhea
- Increased arrhythmias
- Green vision
FAQs
1. What is digoxin mainly used for?
Digoxin is used in heart failure and atrial fibrillation for symptom control and rate control.
2. What is the mechanism of digoxin?
It inhibits Na⁺/K⁺-ATPase, increasing intracellular calcium and cardiac contractility.
3. Why is digoxin called a narrow therapeutic index drug?
Because the toxic dose is close to the therapeutic dose.
4. Does digoxin reduce mortality in heart failure?
No, it improves symptoms but does not reduce mortality.
5. What electrolyte imbalance increases digoxin toxicity?
Hypokalemia significantly increases toxicity risk.
6. What is the antidote for digoxin toxicity?
Digoxin-specific antibody fragments (Digoxin Fab).
7. What are the classic ECG changes with digoxin?
Scooped ST segment and shortened QT interval.
8. Can digoxin be used in renal failure?
Yes, but dose must be reduced and levels monitored.
9. What visual symptom is associated with digoxin toxicity?
Yellow-green discoloration of vision.
10. Is digoxin still relevant today?
Yes, especially in heart failure with atrial fibrillation.
