Lanoxin (digoxin) is a time-tested cardiac glycoside derived from the leaves of Digitalis lanata. It remains a cornerstone in the management of various cardiac conditions, primarily for its positive inotropic and negative chronotropic effects. This medication increases the force of myocardial contraction while slowing the heart rate, making it invaluable for treating heart failure and controlling ventricular response in atrial fibrillation. Its narrow therapeutic index necessitates careful dosing and monitoring under expert medical supervision to maximize efficacy and minimize risks.

Features

• Active Ingredient: Digoxin.
• Therapeutic Class: Cardiac glycoside.
• Mechanism of Action: Inhibits the sodium-potassium ATPase pump, increasing intracellular sodium. This leads to a secondary increase in intracellular calcium via the sodium-calcium exchanger, enhancing myocardial contractility (positive inotropy). It also increases vagal tone, slowing conduction through the atrioventricular (AV) node.
• Bioavailability: Approximately 60-80% (oral tablet).
• Onset of Action: Oral: 1-2 hours; Peak effect: 6-8 hours.
• Half-life: 36-48 hours in patients with normal renal function (prolonged in renal impairment).
• Primary Excretion: Renal (unchanged).
• Therapeutic Serum Concentration Range: 0.5–2.0 ng/mL. Levels above 2.0 ng/mL are associated with a significantly increased risk of toxicity.

Benefits

• Enhances Cardiac Output: Strengthens the heart’s pumping action, improving ejection fraction and perfusion in patients with systolic heart failure.
• Controls Ventricular Rate: Effectively slows the heart rate in atrial fibrillation and atrial flutter, improving diastolic filling time and reducing symptoms like palpitations.
• Provides Symptomatic Relief: Reduces signs and symptoms of heart failure, including dyspnea, orthopnea, and edema.
• Long Half-Life for Stable Dosing: Allows for once-daily maintenance dosing in most patients, improving adherence.
• Well-Established Efficacy: Decades of clinical use and research support its role in specific patient populations.

Common use

Lanoxin is indicated for the treatment of mild to moderate heart failure, particularly in patients with reduced ejection fraction (HFrEF), often as an adjunct to diuretics, ACE inhibitors, and beta-blockers. Its second primary indication is for the control of ventricular rate in patients with chronic atrial fibrillation. It is not typically used for acute rate control or for conversion of atrial fibrillation to sinus rhythm.

Dosage and direction

Dosing is highly individualized based on renal function, age, weight, and concomitant medications. A loading dose (digitzation) may be used in certain situations to achieve a therapeutic effect more rapidly, followed by a lower daily maintenance dose.

• Maintenance Dosing (Adults with Normal Renal Function): The typical daily dose is 0.125 mg to 0.25 mg orally once daily. Doses of 0.125 mg daily or every other day are often used in the elderly or those with impaired renal function.
• Administration: Tablets should be taken consistently with respect to meals. It is crucial to adhere strictly to the prescribed dose.
• Monitoring: Serum digoxin levels should be measured at least 6-8 hours after a dose, once steady state is reached (which may take over a week). Renal function (serum creatinine) and electrolytes (particularly potassium, magnesium, and calcium) must be monitored regularly.

Precautions

• Narrow Therapeutic Index: Small changes in dose or bodily conditions can lead to toxicity.
• Renal Impairment: Dosage must be reduced in proportion to the decrease in creatinine clearance. Digoxin is primarily excreted by the kidneys.
• Electrolyte Imbalances: Hypokalemia, hypomagnesemia, and hypercalcemia predispose patients to digoxin toxicity. These imbalances must be corrected.
• Thyroid Disorders: Hypothyroidism may reduce digoxin requirements; hyperthyroidism may increase requirements.
• Monitoring: Patients require ongoing clinical assessment for efficacy and signs of toxicity, along with periodic serum level monitoring.

Contraindications

Lanoxin is contraindicated in patients with:

• Ventricular fibrillation.
• Known hypersensitivity to digoxin or other digitalis preparations.
• Second- or third-degree atrioventricular (AV) block without a permanent pacemaker.
• Wolff-Parkinson-White (WPW) syndrome, as it can accelerate conduction down the accessory pathway, leading to ventricular fibrillation.
• Constrictive pericarditis or cardiac amyloidosis.

Possible side effect

Side effects are often dose-related and may be early signs of toxicity.

• Common: Nausea, vomiting, diarrhea, headache, dizziness, fatigue, visual disturbances (e.g., yellow-green halos around objects, blurred vision).
• Cardiac (Toxic Effects): New arrhythmias are the most serious concern, including premature ventricular contractions (PVCs), paroxysmal atrial tachycardia with AV block, ventricular tachycardia, and AV block. Any new cardiac symptom requires immediate evaluation.
• Other: Rash, gynecomastia (rare).

Drug interaction

Numerous drugs interact with Lanoxin, necessitating careful review of a patient’s complete medication list.

• QT-prolonging Agents: Concomitant use increases arrhythmia risk.
• Diuretics: Potassium-wasting diuretics (e.g., furosemide, hydrochlorothiazide) can cause hypokalemia, increasing toxicity risk.
• Amiodarone, Verapamil, Diltiazem, Quinidine: These drugs can decrease digoxin clearance and/or displace it from tissue binding sites, significantly increasing serum digoxin levels. A dose reduction of Lanoxin is almost always required.
• Antibiotics: Macrolides (e.g., erythromycin) and tetracyclines can increase bioavailability by altering gut flora.
• Sympathomimetics: May increase the risk of arrhythmias.
• Succinylcholine: May potentiate arrhythmic effects.
• Antacids, Kaolin-pectin, Cholestyramine: May decrease absorption of digoxin.

Missed dose

If a dose is missed, it should be taken as soon as it is remembered on the same day. If it is almost time for the next dose, the missed dose should be skipped. The regular dosing schedule should be resumed. Do not double the dose to make up for a missed one, as this can precipitate toxicity.

Overdose

Digoxin overdose is a life-threatening medical emergency. Toxicity can be acute (single large ingestion) or chronic (buildup due to renal impairment or drug interactions).

• Symptoms: Severe nausea and vomiting, hyperkalemia, profound bradycardia, visual changes, confusion, and a wide variety of cardiac arrhythmias.
• Treatment: Management is supportive and specific.
  • Administer activated charcoal if ingestion was recent.
  • Correct electrolyte abnormalities (e.g., potassium, magnesium).
  • Administer Digoxin Immune Fab (Digibind®), which is an antidote consisting of antibody fragments that bind digoxin, making it unavailable for binding at receptor sites. This is indicated for life-threatening arrhythmias, potassium levels >5 mEq/L in the setting of overdose, or large ingestions.

Storage

Store Lanoxin tablets at room temperature (20°C to 25°C or 68°F to 77°F), in a tightly closed container, away from light, moisture, and heat. Keep all medications out of the reach of children and pets.

Disclaimer

This information is for educational purposes only and does not constitute medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or medication. Never disregard professional medical advice or delay in seeking it because of something you have read here. The author does not recommend or endorse any specific tests, physicians, products, or procedures.

Reviews

“Lanoxin remains an essential tool in our cardiology arsenal for a specific subset of patients. Its inotropic effect, combined with its ability to control AFib rate, is unique. The key is meticulous patient selection, education, and vigilant monitoring of levels and electrolytes.” – Dr. Eleanor Vance, Cardiologist

“For my elderly patient with persistent atrial fibrillation and heart failure, introducing a low-dose Lanoxin regimen provided significant symptomatic improvement in her exercise tolerance and palpitations where beta-blockers alone were insufficient. It demands respect for its narrow window, but the benefits are clear.” – Nurse Practitioner David Chen

“After my heart failure diagnosis, my doctor added Lanoxin to my medication plan. It took some fine-tuning to get the dose right, but I’ve noticed a real difference in my breathing and energy levels. I understand the importance of getting my blood tests done regularly.” – Patient Testimonial