Digoxin and Digoxin Toxicity

Introduction

• Digoxin (brand names: LANOXIN, Digox) is a cardiac glycoside derived from Digitalis purpurea, indicated for the treatment of mild to moderate heart failure and for controlling ventricular rate in chronic atrial fibrillation.
• It is often used in combination with diuretics and angiotensin-converting enzyme (ACE) inhibitors, and dosing must be individualized based on age, renal function, and clinical response.^1-4

Mechanism of Action

• Digoxin inhibits the sodium-potassium ATPase pump, increasing intracellular sodium and calcium in cardiac myocytes, which enhances myocardial contractility (positive inotropy).¹
• It exerts vagomimetic effects, increasing parasympathetic tone and slowing conduction through the sinoatrial and AV nodes, resulting in negative chronotropy and rate control.¹
• Digoxin increases baroreceptor sensitivity, leading to reduced sympathetic outflow and neurohormonal deactivation.¹
• At higher concentrations, it can increase automaticity and efflux of intracellular potassium, potentially raising serum potassium levels.¹

Indications/Clinical Usage

• Heart failure with reduced ejection fraction (mild to moderate): It is used to improve symptoms and exercise tolerance, especially in patients who remain symptomatic despite standard therapy.^1-3
• Pediatric heart failure: It increases myocardial contractility in pediatric patients.^1,3
• Chronic atrial fibrillation: It controls the resting ventricular rate, particularly in patients with concomitant heart failure or those intolerant to beta-blockers or calcium channel blockers.⁴
• Digoxin should be administered with diuretics and ACE inhibitors when possible, and therapeutic effect/toxicity should be closely monitored.^1-3
• Adults with heart failure with reduced ejection fraction or chronic atrial fibrillation: Typical maintenance dose is 0.125–0.25 mg (125–250 mcg) once daily, with lower initial doses (0.0625–0.125 mg) recommended for older adults or those with impaired renal function. Dose titration should be guided by clinical response and serum digoxin concentrations, targeting levels <1.2 ng/mL and ideally 0.5–0.9 ng/mL to minimize toxicity.

Contraindications

• Ventricular fibrillation and other ventricular arrhythmias.¹
• Advanced AV block or sinus node disease without a pacemaker, due to the risk of severe bradycardia or complete heart block.¹
• Acute myocardial infarction: May increase myocardial oxygen demand and precipitate ischemia.¹
• Myocarditis: There is a risk of vasoconstriction and proinflammatory cytokine production.¹
• Restrictive cardiomyopathy, constrictive pericarditis, amyloid heart disease, acute cor pulmonale, idiopathic hypertrophic subaortic stenosis: Digoxin may worsen cardiac output or increase toxicity risk.¹
• Hypersensitivity to digoxin or other digitalis glycosides.^1-3

Adverse Effects/Digoxin Toxicity

• Risk factors for toxicity: Low body weight, advanced age, impaired renal function, hypokalemia, hypomagnesemia, hypercalcemia, drug interactions (e.g., amiodarone, verapamil, macrolides, diuretics).¹
• Incidence: Adverse reactions are dose-dependent. The overall incidence is 5–20%, with 15–20% considered serious.¹
• Presentation: Digoxin toxicity typically presents with
  • Early gastrointestinal symptoms (nausea, vomiting, anorexia),
  • Neurologic changes (headache, confusion, dizziness),
  • Visual disturbances (yellow-green vision), and
  • Arrhythmias such as AV block, atrial tachycardia with block, AV dissociation, ventricular premature contractions, ventricular tachycardia/fibrillation, etc.
• Diagnosis is clinical and supported by electrocardiogram findings (scooped ST segments, flattened or biphasic T waves, shortened QT interval, PR prolongation, and other arrhythmias) (Figure 1). Elevated serum digoxin levels, though toxicity can occur even at levels ≤2 ng/mL in patients with renal impairment or electrolyte abnormalities. Evaluation should include serum electrolytes and renal function, as hyperkalemia indicates severe toxicity.^1,4

Management

• Stop digoxin, correct electrolytes (maintain potassium between 4.0–5.5 mEq/L), place the patient on continuous cardiac monitoring, and treat arrhythmias with atropine, pacing, lidocaine, or phenytoin. Activated charcoal is useful in acute overdose, and dialysis does not remove digoxin.^1-3
• Digoxin immune Fab (Digibind/DigiFab) is the treatment of choice for life-threatening digoxin toxicity, including severe arrhythmias (ventricular tachycardia, ventricular fibrillation), bradycardia, or hyperkalemia. It rapidly binds and neutralizes digoxin, with clinical response rates of 80–90%, and arrhythmia resolution typically occurs within 30–45 minutes.⁵

Anesthetic Considerations

Preoperative Evaluation

• Continuation vs. discontinuation: Digoxin is generally continued perioperatively unless there is evidence of toxicity or a planned procedure (e.g., electrical cardioversion) where temporary discontinuation may reduce arrhythmia risk.⁶
• Renal function assessment: Digoxin is renally excreted; impaired renal function increases toxicity risk. Assess serum creatinine and estimate glomerular filtration rate. Dose adjustment is required for renal impairment, and toxicity may persist longer in these patients.⁶
• Electrolyte assessment: Hypokalemia, hypomagnesemia, and hypercalcemia sensitize the myocardium to digoxin and increase toxicity risk. Correct electrolyte abnormalities preoperatively and monitor levels closely, especially if diuretics or other interacting drugs are used.⁶

Intraoperative Considerations

• Drug interactions: Avoid drugs that increase vagal tone (e.g., neostigmine, succinylcholine) or have additive effects on AV node conduction (e.g., beta-blockers, calcium channel blockers), as these may precipitate bradycardia or heart block.⁶
• Pharmacologic interactions: Be cautious with agents that impair renal function (nonsteroidal anti-inflammatory drugs, angiotensin converting enzyme inhibitors), increase digoxin levels (amiodarone, verapamil, macrolides), or alter electrolyte balance (diuretics, calcium supplements). Rapid intravenous calcium administration can provoke serious arrhythmias in digitalized patients.⁶

Postoperative Considerations

• Resumption of digoxin: If digoxin was withheld preoperatively, restart when the risk of arrhythmia or toxicity is minimized, and renal function/electrolytes are stable. Monitor for signs of toxicity, especially in patients with fluctuating renal function or electrolyte disturbances.⁶