Lanoxin: Restore and Maintain Optimal Heart Rhythm
Lanoxin
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Synonyms | |||
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. By increasing the force of myocardial contraction and slowing the heart rate, it effectively improves cardiac output and controls ventricular response in atrial fibrillation. Its narrow therapeutic index necessitates careful dosing and monitoring, but its efficacy in specific patient populations is well-established.
Features
- Active Ingredient: Digoxin
- Therapeutic Class: Cardiac Glycoside
- Mechanism of Action: Inhibition of the sodium-potassium ATPase pump, leading to increased intracellular sodium and calcium, which enhances myocardial contractility. It also increases vagal tone, slowing conduction through the atrioventricular (AV) node.
- Available Formulations: Oral tablets (62.5 mcg, 125 mcg, 250 mcg), Oral solution (50 mcg/mL), and Injectable solution for IV or IM administration (100 mcg/mL, 250 mcg/mL).
- Bioavailability: Approximately 60-80% for tablets (varies by brand), 70-85% for oral solution.
- Onset of Action: Oral: 1-2 hours; Peak effect: 2-6 hours (may be delayed up to 8-12 hours if a loading dose is not used). IV: 5-30 minutes; Peak effect: 1-4 hours.
- Half-life: 36-48 hours in patients with normal renal function (prolonged in renal impairment).
- Primary Elimination Route: Renal (mostly unchanged).
Benefits
- Enhanced Cardiac Output: Strengthens the heart’s pumping action, making it more efficient at circulating blood throughout the body, which alleviates symptoms of heart failure such as dyspnea and fatigue.
- Control of Ventricular Rate: Effectively slows a rapid heart rate in patients with atrial fibrillation or atrial flutter, improving diastolic filling time and reducing palpitations.
- Long-Term Symptom Management: Provides sustained control of chronic heart failure symptoms, often reducing hospitalizations and improving exercise tolerance.
- Established Safety Profile: With over two centuries of clinical use, its effects, interactions, and toxicity profiles are extensively documented and well-understood by medical professionals.
- Flexible Dosing: Availability in multiple strengths allows for precise titration to achieve individual therapeutic goals while minimizing the risk of toxicity.
Common use
Lanoxin is indicated for the treatment of mild to moderate heart failure in adult patients. It is used to improve left ventricular ejection fraction, increase cardiac output, and lessen the symptoms of heart failure, particularly in patients who remain symptomatic despite adequate doses of diuretics and angiotensin-converting enzyme (ACE) inhibitors. It is also indicated for the control of resting ventricular rate in patients with chronic atrial fibrillation, helping to maintain a hemodynamically stable rhythm.
Dosage and direction
Dosing is highly individualized and MUST be based on ideal body weight, age, and renal function. Therapeutic drug monitoring (measuring serum digoxin concentration) is essential.
- Heart Failure (Adults): The recommended maintenance dose is typically 125 to 250 mcg once daily. For most patients, 125 mcg daily is sufficient. A loading dose (digitzation) may be used in urgent situations but is less common in modern practice.
- Atrial Fibrillation (Adults): The recommended maintenance dose is 125 to 375 mcg once daily. Dosing is titrated to achieve the desired ventricular rate control.
- Administration: Take orally, with or without food. If using the liquid formulation, use the calibrated dropper provided and mix the dose with water or another liquid. Do not crush or chew the tablets.
- Timing: It is generally recommended to take it at the same time each day to maintain stable blood levels.
- Renal Impairment: Dose MUST be reduced in patients with renal impairment. Dosing intervals may be extended (e.g., every 36 or 48 hours) based on calculated creatinine clearance (CrCl).
Precautions
- Narrow Therapeutic Index: The difference between a therapeutic dose and a toxic dose is small. Regular monitoring of serum digoxin levels is critical (therapeutic range is generally 0.5-2.0 ng/mL).
- Renal Function: Digoxin is primarily excreted by the kidneys. Renal function (serum creatinine, CrCl) must be assessed before initiation and monitored periodically during therapy. Dosage adjustments are mandatory in renal impairment.
- Electrolyte Imbalances: Hypokalemia, hypomagnesemia, and hypercalcemia predispose patients to digoxin toxicity, even at normal serum levels. Electrolyte levels must be monitored and corrected, especially when concomitant diuretics are used.
- Thyroid Disorders: Both hypothyroidism and hyperthyroidism can alter a patient’s sensitivity to digoxin. Thyroid function should be evaluated if toxicity is suspected or response is suboptimal.
- Monitoring: Regular assessment of heart rate, rhythm, and clinical signs of heart failure or toxicity is required. Obtain an ECG if toxicity is suspected.
Contraindications
- Ventricular fibrillation.
- Known hypersensitivity to digoxin or other digitalis preparations.
- Second- or third-degree atrioventricular (AV) block (in the absence of a functioning permanent pacemaker).
- Wolff-Parkinson-White (WPW) syndrome (due to risk of paradoxical acceleration of ventricular response).
- Constrictive pericarditis and cardiac amyloidosis.
- Idiopathic hypertrophic subaortic stenosis (IHSS).
Possible side effect
Common side effects are often dose-related and may be early signs of toxicity.
- Cardiac: Bradycardia, AV block, atrial tachycardia with block, ventricular arrhythmias (e.g., premature ventricular contractions, bigeminy, trigeminy, ventricular tachycardia or fibrillation).
- Central Nervous System: Fatigue, malaise, dizziness, headache, insomnia, and, rarely, neuralgia or psychosis.
- Gastrointestinal: Anorexia, nausea, vomiting, diarrhea, abdominal pain.
- Visual: Visual disturbances are classic signs of toxicity, including blurred vision, yellow-green halos around lights (xanthopsia), photophobia, and changes in color perception.
- Other: Gynecomastia (with long-term use).
Drug interaction
Digoxin has numerous significant interactions. A thorough medication review is essential.
- Diuretics (e.g., furosemide, hydrochlorothiazide): Can cause hypokalemia and hypomagnesemia, increasing the risk of toxicity.
- Amiodarone, Quinidine, Verapamil, Diltiazem, Propafenone: These drugs can significantly increase serum digoxin concentrations by reducing its renal or non-renal clearance. A 30-50% reduction in the digoxin dose is often required.
- Macrolide Antibiotics (e.g., erythromycin, clarithromycin), Tetracyclines: Can increase digoxin levels by altering gut flora that metabolize digoxin.
- Antacids, Kaolin-pectin, Cholestyramine, Colestipol: Can decrease the absorption of oral digoxin. Administer digoxin at least 2 hours before or 6 hours after these agents.
- Beta-blockers and Calcium Channel Blockers: Additive effects on AV node conduction can lead to profound bradycardia or heart block.
- Sympathomimetics (e.g., albuterol, epinephrine): Can increase the risk of cardiac arrhythmias.
- Succinylcholine: May potentiate the effects of digoxin and increase the risk of arrhythmias.
Missed dose
If a dose is missed, it should be taken as soon as it is remembered on the same day. However, if it is almost time for the next scheduled dose, the missed dose should be skipped. The regular dosing schedule should be resumed with the next dose. Do not take a double dose to make up for a missed one, as this significantly increases the risk of toxicity.
Overdose
Digoxin overdose is a life-threatening medical emergency. Toxicity can be acute (single large ingestion) or chronic (accumulation due to renal impairment or drug interactions).
- Signs and Symptoms: Severe nausea and vomiting, hyperkalemia, profound bradycardia, advanced heart block, and any type of cardiac arrhythmia (especially ventricular tachycardia or fibrillation). Visual disturbances and confusion are also common.
- Management:
- Immediate Medical Attention: Call emergency services.
- Supportive Care: Continuous cardiac and vital sign monitoring. Correct electrolyte imbalances (e.g., treat hyperkalemia with insulin/glucose, potassium-binding resins; correct hypomagnesemia).
- GI Decontamination: Activated charcoal may be administered if ingestion was recent.
- Digoxin Immune Fab (Digibind®/DigiFab®): This is the specific antidote for serious, life-threatening digoxin toxicity. It binds digoxin molecules, rendering them inactive, and is indicated for hemodynamically unstable arrhythmias, potassium levels >5 mEq/L in acute overdose, or chronically elevated serum digoxin levels (>2 ng/mL) with signs of toxicity.
- Atropine: May be used for symptomatic bradycardia.
- Pacing: Temporary cardiac pacing may be necessary for severe bradycardia or heart block.
Storage
- Store at room temperature (20°C to 25°C or 68°F to 77°F).
- Protect from light and moisture. Keep the bottle tightly closed.
- Keep out of reach of children and pets.
- Do not use after the expiration date printed on the packaging.
- Do not flush medications down the toilet or pour them into a drain. Consult a pharmacist on proper disposal methods.
Disclaimer
This information is for educational and informational 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 before starting, stopping, or changing any prescribed part of your care plan. Never disregard professional medical advice or delay in seeking it because of something you have read here. The author and publisher are not responsible for any specific health or allergy needs that may require medical supervision and are not liable for any damages or negative consequences from any treatment, action, application, or preparation, to any person reading or following the information in this document.
Reviews
- “As a cardiologist with over 30 years of practice, I continue to find Lanoxin invaluable for a specific subset of my heart failure and AFib patients. Its inotropic effect, when used judiciously with careful monitoring, provides a unique benefit that newer agents don’t always replicate. The key is respect for its narrow therapeutic window.” – Dr. A. Reynolds, MD, FACC
- “Managing my father’s chronic atrial fibrillation has been challenging. Since his cardiologist started him on Lanoxin, his heart rate has been consistently under control, and his episodes of palpitations and dizziness have drastically reduced. It has significantly improved his quality of life. We are diligent about his regular blood tests.” – Sarah J.
- “From a clinical pharmacy perspective, Lanoxin demands vigilance. Its numerous and potent drug interactions require us to perform thorough medication reconciliation with every patient encounter. When dosed correctly based on renal function and monitored appropriately, it is a powerful and effective tool, but it is not a ‘set it and forget it’ medication.” – Michael T., PharmD, BCPS