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 vigilant monitoring to ensure efficacy while minimizing the risk of toxicity.

Features

• Active Ingredient: Digoxin.
• Therapeutic Class: Cardiac glycoside.
• Mechanism of Action: Inhibits the sodium-potassium ATPase pump, leading to increased intracellular sodium. This promotes calcium influx via the sodium-calcium exchanger, enhancing myocardial contractility (positive inotropy). It also increases vagal tone, slowing conduction through the atrioventricular (AV) node.
• Available Formulations: Oral tablets (62.5 mcg, 125 mcg, 250 mcg) and injectable solution for IV or IM administration.
• Bioavailability: Approximately 60-80% for oral tablets (varies by brand).
• Onset of Action: Oral: 1-2 hours; IV: 5-30 minutes.
• Time to Peak Effect: Oral: 2-6 hours; IV: 1-4 hours.
• Half-life: 36-48 hours in patients with normal renal function (prolonged in renal impairment).
• Primary Elimination: Renal excretion, predominantly as unchanged drug.

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 like shortness of breath and fatigue.
• Controls Ventricular Rate: Effectively slows a rapid heart rate in patients with atrial fibrillation or atrial flutter, improving ventricular filling and coronary perfusion.
• Reduces Hospitalization: Long-term use in heart failure patients (in conjunction with other therapies) has been shown to reduce the need for hospitalization due to worsening heart failure.
• Symptom Management: Provides significant relief from edema (swelling) and orthopnea (shortness of breath when lying down) associated with congestive heart failure.
• Established Safety Profile: With proper therapeutic drug monitoring, its effects and side effects are well-understood and manageable within a clinical framework.

Common use

Lanoxin is indicated for the treatment of mild to moderate heart failure in adults. It is used to increase myocardial contraction force 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 controlled and regular heart rhythm. It is not typically a first-line agent for either condition but serves as a valuable adjunctive therapy.

Dosage and direction

Dosing is highly individualized and must be based on lean body weight, renal function, age, and concomitant medications. The goal is to achieve and maintain a therapeutic serum digoxin concentration, typically between 0.5 and 0.9 ng/mL.

• Digitalizing (Loading) Dose: Used when a rapid effect is required (e.g., acute atrial fibrillation). A total digitalizing dose (TDD) is administered orally in divided doses over 12-24 hours (e.g., 10-15 mcg/kg lean body weight). IV dosing is approximately 80% of the oral dose.
• Maintenance Dose: Initiated after the loading dose or, more commonly, started without a loading dose for chronic therapy. The typical daily maintenance dose is based on renal function (creatinine clearance). For a patient with normal renal function (CrCl >90 mL/min), a common dose is 125 mcg daily. Doses are often reduced to 62.5 mcg daily or even every other day in the elderly or those with renal impairment.
• Administration: Oral tablets should be taken consistently with respect to meals. The IV formulation must be diluted and administered slowly over at least 5 minutes to avoid precipitous vasoconstriction.
• Monitoring: Serum digoxin levels should be measured at least 6-8 hours after the last dose, once steady state is reached (which may take over a week without a loading dose). Renal function and electrolytes (particularly potassium, magnesium, and calcium) must be monitored regularly.

Precautions

• Renal Impairment: Digoxin is primarily excreted by the kidneys. Dosage must be reduced in proportion to the degree of renal impairment. Frequent monitoring of serum levels is critical.
• Electrolyte Imbalances: Hypokalemia, hypomagnesemia, and hypercalcemia predispose patients to digoxin toxicity, even at “normal” serum levels. These imbalances must be corrected before and during therapy.
• Thyroid Disorders: Hypothyroidism can reduce digoxin clearance, increasing the risk of toxicity. Hyperthyroidism may increase digoxin requirements.
• Underlying Heart Disease: Patients with cardiomyopathy, acute myocardial infarction, or myocarditis may be more sensitive to the arrhythmogenic effects of digoxin.
• Pregnancy and Lactation: Digoxin crosses the placenta and is excreted in breast milk. Use during pregnancy or breastfeeding requires a careful risk-benefit analysis and close monitoring of both mother and infant.

Contraindications

Lanoxin is contraindicated in patients with a known hypersensitivity to digoxin or other digitalis preparations. Its use is also contraindicated in the following conditions:

• Ventricular fibrillation.
• Known or suspected digoxin toxicity.
• Second- or third-degree atrioventricular (AV) block (in the absence of a functioning permanent pacemaker).
• Wolff-Parkinson-White (WPW) syndrome, as digoxin can accelerate conduction through the accessory pathway, leading to ventricular fibrillation.
• Idiopathic hypertrophic subaortic stenosis (IHSS).

Possible side effect

Digoxin has a narrow therapeutic index, and side effects are often dose-related. They can be categorized as cardiac and non-cardiac.

Cardiac Effects:

• New arrhythmias (the most serious side effect).
• PR prolongation.
• SA or AV block.
• Atrial tachycardia with AV block.
• Junctional (nodal) tachycardia.
• Ventricular tachycardia or fibrillation.

Non-Cardiac Effects (often early signs of toxicity):

• Gastrointestinal: Anorexia, nausea, vomiting, diarrhea, abdominal pain.
• Neurological: Fatigue, malaise, headache, dizziness, insomnia, nightmares, agitation.
• Visual: Blurred vision, yellow-green halos around lights (xanthopsia), photophobia.
• Other: Gynecomastia (rare).

Drug interaction

Lanoxin is subject to numerous significant drug interactions that can alter its serum concentration or its effects.

• Increased Digoxin Levels: Amiodarone, quinidine, verapamil, diltiazem, cyclosporine, itraconazole, tetracyclines, propafenone, and macrolide antibiotics (e.g., erythromycin) can significantly increase serum digoxin concentrations.
• Decreased Digoxin Levels: Antacids, kaolin-pectin, sulfasalazine, neomycin, metoclopramide, and some anticancer drugs can decrease digoxin absorption. Thyroxine and phenytoin can increase its metabolism.
• Pharmacodynamic Interactions (Increased Risk of Arrhythmia): Concomitant use with diuretics (causing hypokalemia), sympathomimetics, calcium preparations, succinylcholine, or other antiarrhythmic agents (e.g., beta-blockers, calcium channel blockers) can potentiate the risk of serious 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. 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. Toxicity can be acute (from a single large ingestion) or chronic (from accumulation). Symptoms include severe nausea and vomiting, hyperkalemia, and the cardiac arrhythmias listed above.

• Management: Requires immediate hospitalization and continuous cardiac monitoring.
• Supportive Care: Includes correction of electrolyte imbalances (e.g., potassium, magnesium). Activated charcoal may be effective if administered soon after ingestion.
• Antidote: Digoxin Immune Fab (Digibind®, DigiFab®) is an antibody fragment antidote indicated for potentially life-threatening overdose. It binds to digoxin, rendering it inactive and facilitating its removal from the body.

Storage

Lanoxin tablets should be stored at controlled room temperature (20°-25°C or 68°-77°F), in a tightly closed, light-resistant container, and kept out of reach of children and pets. The injectable solution should be stored according to the manufacturer’s instructions, typically at room temperature and protected from light. Do not use medication beyond the expiration date on the packaging.

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 or for any adverse effects resulting from the use of information contained herein.

Reviews

• “As a cardiologist with over 30 years of practice, I find Lanoxin to be an indispensable tool for a specific subset of my heart failure and AFib patients. Its inotropic effect is predictable, but it demands respect for its narrow therapeutic window. Meticulous dosing and monitoring are non-negotiable.” – Dr. A. Reynolds, MD, FACC
• “This medication gave me my life back. The constant shortness of breath and swelling in my legs from heart failure improved dramatically within a few weeks of starting. My doctor checks my blood levels regularly, and I haven’t had any side effects.” – Patient M., 68
• “From a clinical pharmacy perspective, Lanoxin is a classic example of a drug where pharmacokinetics are paramount. Dosing in renal impairment is our biggest challenge, and we work closely with the cardiology team to use predictive models to get the dose right from the start and prevent toxicity.” – Clinical Pharmacist, Major Hospital Network
• “After my AFib diagnosis, my heart rate was constantly too high. Other medications made me feel tired. Adding a low dose of digoxin finally brought my rate under control without the fatigue. It’s been a key part of my regimen for years.” – Patient R., 72