Makindo Medical Notes

⚠️ Electrolyte imbalance: Hypokalaemia, hypomagnesaemia, and hypercalcaemia all increase the risk of digoxin-induced arrhythmias (via Na⁺/K⁺ ATPase inhibition). Monitor renal function, electrolytes, and serum digoxin levels regularly.

📖 About

• Cardiac glycoside derived from Digitalis species.
• Commonest UK preparation: Digoxin (not digitoxin or ouabain).
• Main indication in UK: rate control in atrial fibrillation (particularly sedentary patients, elderly, or with concomitant heart failure).
• Also used in heart failure with reduced EF for symptomatic relief if symptoms persist despite optimal therapy (ACEi/ARB/ARNI, β-blocker, MRA).

⚙️ Mode of Action

• Inhibits membrane-bound Na⁺/K⁺-ATPase pump.
• ↑ Intracellular sodium → reduced sodium–calcium exchange → ↑ intracellular calcium → positive inotropy.
• Vagomimetic effect: slows AV nodal conduction → ventricular rate control at rest in AF/flutter.
• Less effective for rate control during exertion.
• Excess → ↑ automaticity, after-depolarisations, and arrhythmias.

🩺 Indications & Typical Dosing

• AF with rapid ventricular response: IV loading may be used for acute rate control.
• Chronic AF (sedentary patients): Oral maintenance dosing.
• Heart failure with reduced EF: Symptom relief, not mortality benefit.

💊 Dosing – Digoxin (BNF; verify locally)

🔄 Interactions

• ↑ Digoxin levels: Amiodarone, verapamil, quinidine, macrolides (clarithromycin, erythromycin).
• Electrolyte disturbances: Hypokalaemia (diuretics, steroids), hypomagnesaemia, hypercalcaemia increase toxicity risk.
• Renal impairment: ↓ clearance → ↑ toxicity risk.

🚫 Contraindications

• Wolff–Parkinson–White (WPW) syndrome with AF (may accelerate conduction via accessory pathway → VF).
• Second-/third-degree AV block or severe bradycardia.
• Hypertrophic cardiomyopathy with outflow obstruction.
• Caution: renal failure, elderly, electrolyte disturbances.

❗ Side Effects

• GI: Nausea, vomiting, diarrhoea, abdominal pain.
• CNS: Confusion, fatigue, delirium, psychosis.
• Visual: Blurred vision, yellow-green tinge (“xanthopsia”).
• Arrhythmias: Almost any — classically atrial tachycardia with block, multifocal atrial tachycardia, ventricular ectopics, VT/VF, high-degree AV block, asystole.
• Characteristic ECG: “reverse tick” ST depression, T-wave changes (not always toxic).

🚨 Digoxin Toxicity

• Check serum digoxin levels: aim 0.5–1.0 mcg/L (toxic if >2 mcg/L, though toxicity may occur at lower levels).
• Correct hypokalaemia, hypomagnesaemia; maintain K⁺ >4 mmol/L.
• Digoxin-specific antibody fragments (Digibind) for life-threatening toxicity (severe arrhythmia, hyperkalaemia, haemodynamic instability).
• Avoid DC cardioversion unless absolutely necessary (can trigger VF).
• Pacing may be needed for bradyarrhythmia/AV block.

📚 References

• BNF: Digoxin
• NICE CG180: Atrial fibrillation (management)