Digoxin – Cardiac Glycoside for Heart Failure and Arrhythmias

 

Digoxin is a cardiac glycoside used in heart failure and atrial fibrillation. Learn about its mechanism of action, dosage, side effects, contraindications, brand names, and pricing.

Table of Contents:

1. Introduction  

2. Mechanism of Action  

3. Pharmacokinetics & Dynamics  

4. Indications & Drug of Choice  

5. Contraindications  

6. Side Effects  

7. Drug Interactions  

8. Dosage  

9. Brand Names  

10. Price  

11. Conclusion  

1. Introduction:

*Digoxin* is a *cardiac glycoside* derived from the foxglove plant (*Digitalis lanata*). It has been widely used in the treatment of *congestive heart failure (CHF)* and certain *arrhythmias*, especially *atrial fibrillation*.

2. Mechanism of Action:

Digoxin works by *inhibiting the sodium-potassium ATPase pump* in cardiac cells. This results in:

- ↑ intracellular calcium  

- ↑ myocardial contractility (positive inotropic effect)

- Slows AV node conduction (useful in AF)

3. Pharmacokinetics & Dynamics:

| Bioavailability   | 60–80% orally                      

| Onset             | 30–120 min (oral), 5–30 min (IV)   

| Peak plasma       | 1–3 hours                          |

| Half-life         | 36–48 hours                        |

| Excretion         | Primarily renal (adjust in CKD)    

4. Indications & Drug of Choice:

- *Congestive Heart Failure (CHF)* (with reduced ejection fraction)

- *Atrial Fibrillation (AF)* with rapid ventricular response (rate control)

It is *not the first-line* drug anymore but remains *useful in symptomatic patients despite standard therapy*.

5. Contraindications: 

- Ventricular fibrillation  

- Hypokalemia or hypercalcemia  

- AV block (2nd or 3rd degree without pacemaker)  

- Acute myocardial infarction  

- Renal failure (requires dose adjustment)

6. Side Effects:

- *Cardiac*: Bradycardia, heart block, arrhythmias (especially ventricular)  

- *GI*: Nausea, vomiting, abdominal pain  

- *CNS*: Confusion, visual disturbances (yellow vision – *xanthopsia*)  

- *Toxicity* is a major concern due to narrow therapeutic index

7. Drug Interactions:

 

- *Diuretics* (hypokalemia ↑ toxicity)  

- *Verapamil / Amiodarone / Quinidine* (↑ Digoxin levels)  

- *Beta-blockers* (↑ risk of bradycardia)  

- *Antacids / Cholestyramine* (↓ absorption)

*Monitor serum digoxin and electrolytes regularly.*

8. Dosage:

*Oral (Adults):*  

- Initial: 0.125 to 0.25 mg once daily  

- Maintenance: Adjust based on renal function and serum levels (target: 0.5–2.0 ng/mL)

*IV:*  

- Slow IV bolus over 5 min if rapid digitalization is needed

*Pediatric:*  

- Weight-based dosing; specialist supervision required

9. Brand Names:

- *Lanoxin*  

- *Cardoxin*  

- *Digox*  

- *Digitek*  

- *Toloxin*  

Antidote for Digoxin Toxicity:

The specific antidote for digoxin toxicity is:

*Digoxin-Specific Antibody Fragments (Digibind / DigiFab)*

Brand Names:

- *Digibind*

- *DigiFab*

Mechanism:

Digibind/DigiFab contains Fab antibody fragments that bind free digoxin in the blood, forming inactive complexes that are excreted by the kidneys. This rapidly reduces toxic effects.

Indications for Digoxin Antidote Use:

- Life-threatening arrhythmias (e.g., ventricular tachycardia/fibrillation)

- Severe hyperkalemia (>5.5 mEq/L) with digoxin toxicity

- Digoxin level >10 ng/mL (acute) or >6 ng/mL (chronic)

- Ingestion of a large overdose (especially in children)

- Severe bradycardia or heart block unresponsive to atropine

*Supportive Measures:*

- *Discontinue digoxin*

- *Correct electrolyte imbalances* (esp. potassium & magnesium)

- *Manage arrhythmias* (avoid calcium in digoxin toxicity)

10. Price:

- *USA:* $10–30/month (generic)  

- *India/Pakistan:* Rs. 5–15 per tablet (generic)  

- Available in *tablet, capsule, and injection forms*

11. Conclusion:

 

*Digoxin* remains a valuable medication in select patients with *heart failure* and *atrial fibrillation*, especially those who remain symptomatic. Its *narrow therapeutic window* and *risk of toxicity* necessitate regular monitoring. Clinicians must tailor its use based on renal function, electrolyte status, and drug interactions.