Lanoxin

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 a vital therapeutic agent for controlling ventricular response in atrial fibrillation and for treating heart failure with reduced ejection fraction. Its narrow therapeutic index necessitates careful dosing and vigilant monitoring to ensure efficacy while minimizing the risk of toxicity.

Features

• Active Ingredient: Digoxin.
• Therapeutic Class: Cardiac glycoside, positive inotrope, antiarrhythmic agent (class V).
• Available Formulations: Oral tablets (62.5 mcg, 125 mcg, 250 mcg) and injectable solution for IV or IM administration (100 mcg/mL, 250 mcg/mL).
• Mechanism of Action: Inhibits the sodium-potassium ATPase pump, leading to increased intracellular sodium. This increase facilitates sodium-calcium exchange, resulting in elevated intracellular calcium concentrations, which enhances myocardial contractility. It also increases vagal tone, slowing conduction through the atrioventricular (AV) node.
• Bioavailability: Oral tablets have a bioavailability of 60-80% (tablets) and 90-100% (elixir).
• Half-life: Approximately 36-48 hours in patients with normal renal function, allowing for once-daily dosing.
• Therapeutic Range: 0.5-2.0 ng/mL. Serum concentrations >2.0 ng/mL are associated with a significantly increased risk of toxicity.

Benefits

• Improves Cardiac Output: Enhances the strength of the heart’s contractions, allowing it to pump blood more effectively throughout the body, which alleviates symptoms of heart failure such as dyspnea and fatigue.
• Controls Ventricular Rate: Effectively slows a rapid heart rate in patients with atrial fibrillation or atrial flutter, improving cardiac efficiency and reducing palpitations.
• Long-Term Symptom Management: Provides sustained control of chronic cardiac conditions, improving exercise tolerance and overall quality of life.
• Proven Efficacy: Possesses a well-documented history of clinical use and a deep understanding of its pharmacodynamics among healthcare professionals.
• Oral Administration: The availability of an oral tablet formulation supports long-term outpatient management and patient adherence.

Common use

Lanoxin is indicated for the treatment of mild to moderate heart failure in adult patients. It is used to increase myocardial contractility and improve left ventricular ejection fraction, particularly in patients who remain symptomatic despite adequate doses of diuretics, ACE inhibitors, and beta-blockers. Its second primary indication is 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 lean body weight, age, and renal function. A loading dose (digitzation) may be used in urgent situations to achieve a therapeutic effect rapidly, followed by a lower maintenance dose.

• Maintenance Dosing (Adults with Normal Renal Function): The typical daily maintenance dose is 125 mcg to 250 mcg (0.125 mg to 0.25 mg) orally once daily.
• Dosing in Renal Impairment: Dose reduction is mandatory. Dosing intervals may be extended (e.g., 125 mcg every 48 hours) or the dose itself lowered based on calculated creatinine clearance (CrCl).
• Geriatric Patients: Often require reduced doses (e.g., 125 mcg daily or every other day) due to age-related decline in renal function and lean body mass.
• Administration: Tablets should be taken consistently with respect to meals to minimize variability in absorption. It is crucial to monitor serum digoxin levels approximately 6-8 hours post-dose after steady-state is reached (which may take over a week), ensuring they remain within the therapeutic window.

Precautions

• Narrow Therapeutic Index: Lanoxin has a very small margin between therapeutic and toxic doses. Meticulous dosing and regular monitoring of serum digoxin levels, electrolytes (especially potassium, magnesium, and calcium), and renal function are imperative.
• Hypokalemia/Hypomagnesemia: Low potassium or magnesium levels potentiate the toxic effects of digoxin, increasing the risk of serious arrhythmias. Levels must be corrected and maintained within normal limits.
• Renal Impairment: Digoxin is primarily excreted unchanged by the kidneys. Any impairment in renal function will prolong its half-life and lead to accumulation, necessitating dose adjustment.
• Thyroid Disorders: Both hypothyroidism and hyperthyroidism can alter sensitivity to digoxin. Dose requirements may change with treatment of the thyroid condition.
• Monitoring: Patients require regular clinical assessment for signs and symptoms of both efficacy and toxicity, including heart rate, rhythm, and review of symptoms.

Contraindications

Lanoxin is contraindicated in the following conditions:

• 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 paradoxically accelerate ventricular response.
• Idiopathic hypertrophic subaortic stenosis (IHSS).

Possible side effect

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

• Cardiac: New arrhythmias (e.g., PVCs, PAT with block, ventricular tachycardia, AV block, bradycardia).
• Central Nervous System: Fatigue, malaise, dizziness, headache, insomnia, and, rarely, visual disturbances (e.g., yellow-green halos around objects - xanthopsia).
• Gastrointestinal: Anorexia, nausea, vomiting, diarrhea, abdominal pain.
• Other: Gynecomastia (rare).

Drug interaction

Numerous drugs interact with Lanoxin, primarily affecting its serum concentration.

• Increase Digoxin Levels: Amiodarone, verapamil, diltiazem, quinidine, propafenone, macrolide antibiotics (e.g., erythromycin), tetracyclines, itraconazole, alprazolam, and spironolactone.
• Decrease Digoxin Levels: Antacids, kaolin-pectin, sulfasalazine, neomycin, metoclopramide, and some anticancer drugs.
• Pharmacodynamic Interactions (Increased Toxicity Risk): Diuretics (cause hypokalemia), beta-blockers, and calcium channel blockers (additive effects on heart rate and AV conduction). Sympathomimetics can 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 patient should never 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. Manifestations include severe nausea and vomiting, hyperkalemia, and a wide variety of cardiac arrhythmias (e.g., severe bradycardia, AV block, ventricular tachycardia/fibrillation). Treatment is multifaceted:

• Immediate Care: Administer activated charcoal if ingestion was recent.
• Correct Electrolytes: Carefully manage potassium levels; avoid giving potassium if AV block is present.
• Administer Digoxin Immune Fab (Digibind®): This is the specific antidote for serious, life-threatening digoxin toxicity. It binds digoxin molecules, rendering them inactive.
• Symptomatic Support: Management of arrhythmias with appropriate medications (e.g., phenytoin, lidocaine) may be necessary.

Storage

Store Lanoxin tablets at room temperature (20°-25°C or 68°-77°F), in a tightly closed container, and away from excess light, heat, and moisture. Keep all medications out of the reach of children and pets. Do not flush unused medication down the toilet or pour it into a drain.

Disclaimer

This information is for educational purposes only and 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 or stopping any medication. Never disregard professional medical advice or delay in seeking it because of something you have read here.

Reviews

“Lanoxin remains an invaluable tool in our cardiology arsenal. Its predictable pharmacokinetics, when managed correctly, provide excellent rate control in AFib and offer a synergistic effect in heart failure management. The key, without question, is vigilant monitoring of levels and renal function.” – Cardiologist, 15 years of experience

“For a subset of my older heart failure patients who are not candidates for or tolerate other therapies, digoxin is a workhorse. It reliably improves their symptoms and functional capacity. Managing the narrow window requires a disciplined approach from both the clinician and the patient.” – Internal Medicine Physician

“While newer agents have emerged, the role of digoxin is well-established. Its low cost and efficacy ensure it stays relevant, particularly in resource-limited settings or for specific patient phenotypes. Understanding its interactions is non-negotiable for safe prescribing.” – Clinical Pharmacist Specialist