#lanoxin

Common Brand Names: Lanoxin

Therapeutic Class: Class IV antiarrhythmic

Common Injectable Dosage Forms:

Injection: 0.1 mg/mL pediatric injection and 0.25 mg/mL in ampules and syringes

Dosage Ranges:

For full digitalization in adults with normal renal function, loading doses of 8-12 mcg/kg are usually administered by giving 50% of the total dose as the first dose, then 25% at 4 hours, and another 25% at 8 hours. Maintenance doses are based on therapeutic response and can be estimated by the following formula: daily % loss = 14 + CrCl( (mL/min)/5

Pediatric and neonatal digitalization doses generally range from 15-50 mcg/kg based on age, with maintenance doses generally 20-35% of loading dose.

Therapeutic Drug Level: Between 0.5 and 2 nanograms/mL

Administration and Stability: IM administration of digoxin is not generally done due to severe local reactions at injection sites and unpredictable absorption and should be given slowly over a period of at least 5 minutes or diluted 4-fold with a compatible solution (sterile water, NS) and given over the same period. Stable for 48 hours at room temperature and refrigerated in concentrations of 250 mcg/100 mL with D5W or NS. pH 6.8-7.2

Pharmacology/Pharmacokinetics: While the exact mechanism of digoxin has not been fully elucidated, it is thought the main activity is related to direct action on the force and velocity of myocardial systolic contractions. This increases cardiac output and reflexively reduces heart rate and causes diuresis in edematous patients. It also decreases conduction velocity through the AV node. Digoxin is widely distributed in body tissues, with 20-30% being serum protein bound. It is excreted in the urine primarily as unchanged drug, with an average elimination half-life of 34-44 hours.

Drug and Lab Interactions: DIURETICS which cause electrolyte disturbances may also produce glycoside toxicity. Concomitant IV administration with calcium supplements may cause arrhythmias. QUINIDINE, FLECAINIDE, and AMIODARONE may increase serum digoxin levels and lead to toxicity. Other drugs leading to increased digoxin levels include verapamil and indomethacin. Concomitant use with sympathomimetics may increase risk of arrhythmias.

Contraindications/Precautions: Digoxin is contraindicated in patients with ventricular fibrillation. The drug should be used with caution in many patients with certain types of arrhythmias, as the cardiac glycosides may be arrhythmogenic. Use with caution when IV is given to hypertensive patients, as it may cause transient elevations in blood pressure. Pregnancy Category C.

Monitoring Parameters: Digoxin serum concentrations, heart rate and rhythm, serum potassium, magnesium, and calcium, renal function, noncardiac signs of toxicity (confusion, depression).

Adverse Effects: The main risk of adverse effects with digoxin use is toxicity, and levels should be carefully monitored. Toxicity may manifest itself as GI effects (nausea, vomiting, and anorexia), CNS effects (headache, visual disturbances, malaise), hyperkalemia, and arrhythmias. Other effects reported include gynecomastia, vaginal changes, and local cutaneous reactions.

Brand Names: Lanoxin, Digitek

Generic Available

Common Dosage Forms:

Tablets: 0.125 mg and 0.25 mg

Elixir Pediatric: 0.05 mg/1 mL (10% alcohol).

Injection: 0.1 mg or 0.25 mg/mL (1 or 2 mL ampules).

FDA Indications/Dosages*:

For the treatment of heart  failure, atrial fibrillation, atrial flutter, and paroxysmal tachycardia: Doses must be individualized and depend on the type and severity of the disease, age weight of the patient, renal function, and concomitant disease states. Normal dosage range is 0.125 mg to 0.5 mg a day in a single dose.

*See manufacturer’s package insert for complete dosing information on loading doses, pediatric use, injectable doses, and other factors with influence the dose.

Monitor: Serum digoxin.

Pharmacology/Pharmacokinetics: Digitalis glycosides inhibit membrane bound Na+/K+ ATPase resulting in an increased intracellular K+ concentration. The increased intracellular Na+ leads to an influx of extracellular Ca++. The net result is an increase in the force and velocity of systolic contractions, a slowing of heart rate, and a decreased conduction velocity through the AV node. Onset of action occurs in 5-30 minutes after an IV dose with a time to peak effect of 1-4 hours. Up to 25-30% is bound to plasma proteins. Digoxin follows first-order kinetics with a half-life of 1.5-2 days.

Drug Interactions: Electrolyte disturbances caused by DIURETICS may cause arrhythmias. Serum levels are increased in hypothyroidism (thioamides) and decreased in hyperthyroidism. Aminoglycosides, antineoplastic agents, cholestyramine, colestipol, metoclopramide, and penicillamine may decrease serum levels. AMIODARONE, QUINIDINE, PROPAFENONE, and ERYTHROMYCIN increase serum levels. CYCLOSPORINE, TETRACYCLINES, and quinine may increase serum levels. Digoxin and VERAPAMIL have additive effects.

Contraindications/Precautions: Use is contraindicated with ventricular fibrillation. Use with caution in pregnancy or nursing mothers and in patients with severe carditis, heart failure accompanying acute glomerulonephritis, renal impairment, hypokalemia, hypomagnesemia, hypercalcemia, acute myocardial infarction, pulmonary disease, incomplete AV block, sinus node defects, and patients with idiopathic hypertrophic subaortic stenosis. Pregnancy Category C.

Adverse Effects: Anorexia, nausea, vomiting, gynecomastia, blurred vision, headache, and bradycardia.

Patient Consultation:

Do not discontinue medication without first consulting physician.

Do not take any nonprescription cough or cold medicines, antacids, laxatives, or antidiarrheals without first consulting your pharmacist or physician.

Store in a cool, dry place away from sunlight and children.

If a dose is missed, take it as soon as possible. If it is closer to the time of your next dose than the dose you missed, skip the missed dose and return to your dosing schedule.