Digoxin

1. Introduction

Digoxin is a cardiac glycoside used to manage heart conditions such as atrial fibrillation and heart failure. It enhances myocardial contractility by inhibiting the sodium-potassium ATPase pump, increasing intracellular calcium levels, and improving cardiac output. Additionally, it slows conduction through the atrioventricular (AV) node, controlling heart rate in atrial fibrillation.

2. Indications

  • Approved Indications:
    • Heart failure with reduced ejection fraction (HFrEF), particularly in patients with persistent symptoms despite optimal therapy.
    • Rate control in atrial fibrillation and atrial flutter.
  • Off-Label Uses:
    • Management of supraventricular tachycardias (SVTs).

3. Dosage

  • Adults:
    • Heart Failure: 125–250 mcg once daily. Adjust based on renal function and response.
    • Atrial Fibrillation: 125–500 mcg once daily, titrated according to clinical response and serum levels.
  • Children:
    • Loading dose: 10–15 mcg/kg (given in divided doses over 24 hours).
    • Maintenance dose: 2.5–5 mcg/kg/day in divided doses, adjusted by age and renal function.
  • Renal Impairment:
    • Dose reduction is necessary, as digoxin is primarily renally excreted.

4. Administration

  • Take orally with water, with or without food.
  • For IV administration, inject slowly over at least 5 minutes.
  • Avoid rapid IV administration, as it may lead to arrhythmias.

5. Forms Available

  • Tablets: 62.5 mcg, 125 mcg, 250 mcg.
  • Oral solution: 50 mcg/mL.
  • Intravenous solution: 250 mcg/mL.

6. Side Effects

6.1. Common Side Effects

  • Nausea and vomiting.
  • Dizziness or fatigue.
  • Visual disturbances (e.g., blurred vision, yellow-green halos).

6.2. Less Common Side Effects

  • Bradycardia.
  • Confusion or mental disturbances.

6.3. Rare but Serious Side Effects

  • Ventricular arrhythmias.
  • Digoxin toxicity, particularly in patients with renal impairment.

7. Warnings

  • Digoxin Toxicity: Narrow therapeutic index; toxicity may occur with serum levels >2 ng/mL or at lower levels in susceptible patients. Symptoms include nausea, confusion, arrhythmias, and visual disturbances.
  • Electrolyte Imbalances: Hypokalaemia, hypomagnesaemia, and hypercalcaemia increase the risk of toxicity.
  • Renal Impairment: Digoxin clearance is reduced; dosage adjustment is critical.

8. Precautions

  • Monitor for signs of toxicity, especially in elderly patients or those with impaired renal function.
  • Use with caution in patients with sick sinus syndrome or AV block.
  • Avoid use in patients with Wolff-Parkinson-White syndrome and pre-excitation syndromes.

9. Interactions

  • Drug-Drug Interactions:
    • Diuretics: Increase risk of hypokalaemia and toxicity.
    • Amiodarone, verapamil, and quinidine: Increase digoxin levels.
    • Rifampin and phenytoin: Reduce digoxin levels.
  • Drug-Food Interactions:
    • High-fibre meals may reduce digoxin absorption.

10. Monitoring Parameters

  • Serum digoxin levels (therapeutic range: 0.5–2 ng/mL).
  • Renal function (e.g., serum creatinine, estimated glomerular filtration rate).
  • Electrolytes (potassium, magnesium, calcium).
  • Heart rate and rhythm (ECG monitoring if indicated).

11. Use in Children

  • Safe for use in children when dosed appropriately. Close monitoring is required due to the narrow therapeutic window.

12. Use in Pregnancy

  • Category C: Use only if the benefits outweigh the risks. No evidence of teratogenic effects, but toxicity may cause maternal and foetal complications.

13. Use in Elderly

  • Use with caution due to increased risk of toxicity. Start at the lowest effective dose and monitor renal function and serum levels closely.

14. Use in Kidney Disease

  • Dose adjustments are essential in renal impairment due to reduced clearance. Toxicity is more likely in patients with poor renal function.

15. Use in Liver Disease

  • No specific dose adjustment is required for hepatic impairment, as digoxin is primarily renally excreted.

16. Patient Counselling Points

  • Take digoxin exactly as prescribed. Do not take extra doses to make up for missed doses.
  • Report symptoms of toxicity, such as nausea, vomiting, visual changes, or irregular heartbeats, immediately.
  • Avoid high-fibre meals close to taking your dose, as they may reduce absorption.
  • Inform your healthcare provider of all other medications, including over-the-counter drugs and supplements.
  • Keep regular follow-up appointments for blood tests and ECGs.

17. Table of Brand Names, Manufacturers, and Prices

Brand NameManufacturerPrice (USD)
LanoxinGlaxoSmithKline$20–40 (30 tablets, 125 mcg)
DigitekUCB Pharma$15–30 (30 tablets, 125 mcg)
Generic DigoxinVarious$10–20 (30 tablets, 125 mcg)

18. FAQs (15 Questions)

  1. What is digoxin used for?
    Digoxin is used to manage heart failure and control heart rate in atrial fibrillation.
  2. How does digoxin work?
    It increases the force of heart contractions and slows the heart rate by inhibiting the sodium-potassium ATPase pump.
  3. What are the common side effects of digoxin?
    Nausea, vomiting, dizziness, and visual disturbances are common.
  4. How should digoxin be taken?
    Take it orally with water, at the same time each day. Avoid high-fibre meals close to dosing.
  5. What are the signs of digoxin toxicity?
    Symptoms include nausea, confusion, irregular heartbeats, and yellow-green vision changes.
  6. Can digoxin be stopped suddenly?
    No, abrupt discontinuation may worsen heart failure or arrhythmias. Consult your doctor before stopping.
  7. How is digoxin monitored?
    Serum digoxin levels, kidney function, electrolytes, and heart rate are routinely monitored.
  8. Can digoxin interact with other medications?
    Yes, it interacts with diuretics, amiodarone, verapamil, and many other drugs.
  9. Is digoxin safe in pregnancy?
    It may be used if necessary, but it requires close monitoring to avoid maternal and foetal toxicity.
  10. What should I do if I miss a dose of digoxin?
    Take it as soon as you remember, but skip it if it’s close to the next dose. Do not double up.
  11. Can digoxin cause kidney damage?
    No, but poor kidney function can lead to digoxin accumulation and toxicity.
  12. Can digoxin cause weight gain?
    No, weight gain is not a direct side effect. However, worsening heart failure can cause fluid retention and weight gain.
  13. What foods should I avoid while taking digoxin?
    Avoid high-fibre meals around dosing times, as they can reduce absorption.
  14. How long does digoxin take to work?
    Improvement in heart rate may be seen within hours, but full benefits for heart failure may take weeks.
  15. How should digoxin be stored?
    Store at room temperature, away from light and moisture.