Digoxin

1 INDICATIONS AND USAGE Digoxin is a cardiac glycoside indicated in adults for the treatment of mild to moderate heart failure and for the control of resting ventricular rate in patients with chronic atrial fibrillation. ( 1.1 , 1.3 ) In pediatric patients with heart failure, digoxin is indicated to increase myocardial contractility. ( 1.2 ) 1.1 Heart Failure in Adults Digoxin Oral Solution is indicated for the treatment of mild to moderate heart failure. Digoxin increases left ventricular ejection fraction and improves heart failure symptoms as evidenced by increased exercise capacity and decreased heart failure-related hospitalizations and emergency care, while having no effect on mortality. Where possible, digoxin should be used with a diuretic and an angiotensin-converting enzyme inhibitor, but an optimal order for starting these three drugs cannot be specified. 1.2 Heart Failure in Pediatric Patients Digoxin is indicated to increase myocardial contractility in pediatric patients with heart failure. 1.3 Atrial Fibrillation in Adults Digoxin Oral Solution is indicated for the control of resting ventricular response rate in patients with chronic atrial fibrillation. Digoxin should not be used for the treatment of multifocal atrial tachycardia.

2 DOSAGE AND ADMINISTRATION Toxic levels of digoxin are only slightly higher than therapeutic levels. The pharmacokinetics of digoxin are complex and dose determination should take into account patient-specific factors (age, lean body weight, renal function, etc.). (2.4 , 2.5) Patients should be monitored for toxicity and therapeutic effect and doses should be adjusted, accordingly. (2.2) 2.1 General Dosing Considerations The dose of digoxin should be based on clinical assessment but individual patient factors should be taken into consideration. Those factors are: Lean body weight Renal function Patient age Concurrent disease [see Warnings and Precautions (5) ] Concomitant medication [see Drug Interactions (7) ] Because the pharmacokinetics of digoxin are complex, and because toxic levels of digoxin are only slightly higher than therapeutic levels, digoxin dosing can be difficult. The recommended approach is to: estimate the patient’s daily maintenance dose adjust the estimate to account for patient-specific factors choose a dosing regimen decide whether to initiate therapy with a loading dose monitor the patient for toxicity and for therapeutic effect adjust the dose Dose titration may be accomplished by either of two general approaches that differ in dosage and frequency of administration, but reach the same total amount of digoxin accumulated in the body. If rapid titration is considered medically appropriate, administer a loading dose based upon projected peak digoxin body stores. Maintenance dose can be calculated as a percentage of the loading dose. More gradual titration may be obtained by beginning an appropriate maintenance dose, thus allowing digoxin body stores to accumulate slowly. Steady-state serum digoxin concentrations will be achieved in approximately five half-lives of the drug for the individual patient. Depending upon the patient’s renal function, this will take between 1 and 3 weeks. 2.2 Serum Digoxin Concentrations In general, the dose of digoxin used should be determined on clinical grounds. However, measurement of serum digoxin concentrations can be helpful to the clinician in determining the adequacy of digoxin therapy and in assigning certain probabilities to the likelihood of digoxin intoxication. Studies have shown diminished efficacy at serum levels 10 Years of Age and Adults Number of Days Before Lean Body Weight Lean Body Weight kg 5 10 20 30 40 50 60 40 50 60 70 80 90 100 Steady State Achieved lb 11 22 44 66 88 110 132 88 110 132 154 176 198 220 10 10 20 40 60 80 100 120 80 100 120 140 160 180 200 19 20 11 23 45 68 90 113 135 90 113 135 158 180 203 225 16 30 13 25 50 75 100 125 150 100 125 150 175 200 225 250 14 40 14 28 55 83 110 138 165 110 138 165 193 220 248 275 13 50 15 30 60 90 120 150 180 120 150 180 210 240 270 300 12 60 16 33 65 98 130 163 195 130 163 195 228 260 293 325 11 70 18 35 70 105 140 175 210 140 175 210 245 280 315 350 10 80 19 38 75 113 150 188 225 150 188 225 263 300 338 375 9 90 20 40 80 120 160 200 240 160 200 240 280 320 360 400 8 100 21 43 85 128 170 213 255 170 213 255 298 340 383 425 7 The doses are rounded to whole numbers. Twice daily dosing is recommended for pediatric patients under 10 years of age. Once daily dosing is recommended for pediatric patients above 10 years of age and adults. Ccr is creatinine clearance, corrected to 70 kg body weight or 1.73 m 2 body surface area. For adults , if only serum creatinine concentrations (Scr) are available, a Ccr (corrected to 70 kg body weight) may be estimated in men as (140 – Age)/Scr. For women, this result should be multiplied by 0.85. Note : This equation cannot be used for estimating creatinine clearance in infants or pediatric patients. For pediatric patients , the modified Schwartz equation may be used as listed below. The formula was based on height in cm and Scr in mg/dL where k is a constant. Ccr is corrected to 1.73 m 2 body surface area. During the first year of life, the value of k is 0.33 for pre-term babie …

3 DOSAGE FORMS AND STRENGTHS Each 1 mL of clear, colorless Digoxin Oral Solution contains 0.05 mg (50 mcg). The Digoxin Oral Solution bottles are to be used with the graduated droppers provided in the carton. Starting at 0.2 mL, this 1 mL dropper is marked in divisions of 0.1 mL, corresponding to 5 mcg or 0.005 mg of digoxin. The calibrated dropper supplied with the 60 mL bottle of Digoxin Oral Solution is not appropriate to measure doses below 0.2 mL. Doses less than 0.2 mL require appropriate methods or measuring devices designed to administer an accurate amount to the patient, such as a graduated syringe. NOTE: Oral Solution: Each 1 mL contains 0.05 mg (50 mcg) of digoxin. (3)

4 CONTRAINDICATIONS Allergy to digoxin is rare. Digoxin is contraindicated in patients with a known hypersensitivity to digoxin or other forms of digitalis. Digitalis glycosides, such as digoxin, are contraindicated in ventricular fibrillation. • Known hypersensitivity to digoxin or other forms of digitalis. ( 4 ) • Ventricular fibrillation. ( 4 )

6 ADVERSE REACTIONS The frequency and severity of adverse reactions to digoxin when taken orally depend on the dose and the patient's underlying disease or concomitant therapies [see Warnings and Precautions (5) and Drug Interactions (7) ]. The overall incidence of adverse reactions has been reported as 5% to 20%, with 15% to 20% of them being considered serious (1% to 4% of patients receiving digoxin). Evidence suggests that the incidence of toxicity has decreased since the introduction of the serum digoxin assay and improved standardization of digoxin tablets. Cardiac toxicity accounts for about one-half, gastrointestinal disturbances for about one-fourth, and CNS and other toxicity for about one-fourth of these adverse reactions. Adverse reactions are less common when digoxin is used within the recommended dose range or therapeutic serum concentration range and when there is careful attention to concurrent medications and conditions. The overall incidence of adverse reactions with digoxin has been reported as 5% to 20%, with 15% to 20% of adverse events considered serious. Cardiac toxicity accounts for about one-half, gastrointestinal disturbances for about one-fourth, and CNS and other toxicity for about one-fourth of these adverse events. ( 6 ) To report SUSPECTED ADVERSE REACTIONS, contact Hikma Pharmaceuticals USA Inc. at 1-800-962-8364 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch . 6.1 Cardiac In adults, high doses of digoxin may produce a variety of electrocardiographic changes and rhythm disturbances, such as first-degree, second-degree (Wenckebach), or third-degree heart block (including asystole); atrial tachycardia with block; AV dissociation; accelerated junctional (nodal) rhythm; unifocal or multifocal ventricular premature contractions (especially bigeminy or trigeminy); ventricular tachycardia; and ventricular fibrillation. Prophylactic use of a cardiac pacemaker may be considered if the risk of heart block is considered unacceptable. In pediatric patients, the use of digoxin may produce arrhythmias. The most common are conduction disturbances or supraventricular tachyarrhythmias, such as atrial tachycardia (with or without block) and junctional (nodal) tachycardia. Ventricular arrhythmias are less common. Sinus bradycardia may be a sign of impending digoxin intoxication, especially in infants, even in the absence of first-degree heart block. Any arrhythmias or alteration in cardiac conduction that develops in a child taking digoxin should initially be assumed to be a consequence of digoxin intoxication. 6.2 Gastrointestinal Anorexia, nausea, vomiting and diarrhea may be early symptoms of digoxin toxicity. However, uncontrolled heart failure may also produce such symptoms. The use of digoxin has been associated with abdominal pain, intestinal ischemia, and hemorrhagic necrosis of the intestines. 6.3 CNS and Special Senses Digoxin can produce visual disturbances (blurred vision, green-yellow color disturbances, halo effect), headache, weakness, dizziness, apathy, confusion, and mental disturbances (such as anxiety, depression, delirium, and hallucination). 6.4 Other Gynecomastia has been reported following the prolonged use of digoxin. Thrombocytopenia, maculopapular rash and other skin reactions have been observed.

7 DRUG INTERACTIONS Digoxin has a narrow therapeutic index, increased monitoring of serum digoxin concentrations and for potential signs and symptoms of clinical toxicity is necessary when initiating, adjusting, or discontinuing drugs that may interact with digoxin. Prescribers should consult the prescribing information of any drug which is co-prescribed with digoxin for potential drug interaction information. • PGP Inducers/Inhibitors: Drugs that induce or inhibit PGP have the potential to alter digoxin pharmacokinetics. ( 7.1 ) • The potential for drug-drug interactions must be considered prior to and during drug therapy. ( 7.2 , 7.3 , 12.3 ) 7.1 P-Glycoprotein (PGP) Inducers/Inhibitors Digoxin is a substrate for P-glycoprotein, at the level of intestinal absorption, renal tubular section and biliary-intestinal secretion. Therefore, drugs that induce/inhibit P-glycoprotein have the potential to alter digoxin pharmacokinetics. 7.2 Pharmacokinetic Drug Interactions on Serum Digoxin Levels in Adults Digoxin Concentrations Increased Greater than 50% Digoxin Serum Concentration Increase Digoxin AUC Increase Recommendations Amiodarone 70% NA Measure serum digoxin concentrations before initiating concomitant drugs. Reduce digoxin dose by approximately 30% to 50% or by modifying the dosing frequency and continue monitoring. Captopril 58% 39% Clarithromycin NA 70% Dronedarone NA 150% Gentamicin 129 to 212% NA Erythromycin 100% NA Itraconazole 80% NA Lapatinib NA 180% Propafenone NA 60 to 270% Quinidine 100% NA Ranolazine 50% NA Ritonavir NA 86% Telaprevir 50% 85% Tetracycline 100% NA Verapamil 50 to 75% NA Digoxin Concentrations Increased Less than 50% Atorvastatin 22% 15% Measure serum digoxin concentrations before initiating concomitant drugs. Reduce digoxin dose by approximately 15% to 30% or by modifying the dosing frequency and continue monitoring. Carvedilol 16% 14% Conivaptan 33% 43% Diltiazem 20% NA Indomethacin 40% NA Mirabegron 29% 27% Nefazodone 27% 15% Nifedipine 45% NA Propantheline 24% 24% Quinine NA 33% Rabeprazole 29% 19% Saquinavir 27% 49% Spironolactone 25% NA Telmisartan 20 to 49% NA Ticagrelor 31% 28% Tolvaptan 30% 20% Trimethoprim 22 to 28% NA Digoxin Concentrations Increased, but Magnitude is Unclear Alprazolam, Azithromycin, Cyclosporine, Diclofenac, Diphenoxylate, Epoprostenol, Esomeprazole, Ibuprofen, Ketoconazole, Lansoprazole, Metformin, Omeprazole Measure serum digoxin concentrations before initiating concomitant drugs. Continue monitoring and reduce digoxin dose as necessary. Digoxin Concentrations Decreased Acarbose, Activated Charcoal, Albuterol, Antacids, certain cancer chemotherapy or radiation therapy, Cholestyramine, Colestipol, Exenatide, Kaolin-pectin, Meals High in Bran, Metoclopramide, Miglitol, Neomycin, Penicillamine, Phenytoin, Rifampin, St. John’s Wort, Sucralfate, Sulfasalazine Measure serum digoxin concentrations before initiating concomitant drugs. Continue monitoring and increase digoxin dose by approximately 20% to 40% as necessary. NA – Not available/reported 7.3 Pharmacodynamic Drug Interactions Antiarrhythmics Dofetilide Concomitant administration with digoxin was associated with a higher rate of torsades de pointes . Sotalol Proarrhythmic events were more common in patients receiving sotalol and digoxin than on either alone; it is not clear whether this represents an interaction or is related to the presence of CHF, a known risk factor for proarrhythmia, in patients receiving digoxin. Parathyroid Hormone Analog Teriparatide Sporadic case reports have suggested that hypercalcemia may predispose patients to digitalis toxicity. Teriparatide transiently increases serum calcium. Thyroid Supplement Thyroid Treatment of hypothyroidism in patients taking digoxin may increase the dose requirements of digoxin. Sympathomimetics Epinephrine Can increase the risk of cardiac arrhythmias. Norepinephrine Dopamine Neuromuscular Blocking Agents Succinylcholine May cause sudden extrusion of potassium …

8 USE IN SPECIFIC POPULATIONS • Geriatric Patients ( 8.5 ): Use caution during dose selection, taking into account renal function, and carefully monitor for side effects. • Renal Impairment ( 8.7 ): Digoxin is excreted by the kidneys. Renal function should be considered during dosage selection. 8.1 Pregnancy Risk Summary Experience with digoxin in pregnant women over several decades, based on published retrospective clinical studies and case reports, has not led to the identification of a drug associated risk of major birth defects, miscarriage or adverse maternal and fetal outcomes. Untreated underlying maternal conditions, such as heart failure and atrial fibrillation, during pregnancy pose a risk to the mother and fetus (see Clinical Consideration). Animal reproduction studies have not been conducted with digoxin. The estimated background risk of major birth defects and miscarriage for the indicated population(s) are unknown. All pregnancies have a background risk of birth defect, loss, or other adverse outcomes, In the U.S. General population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2-4% and 15-20%, respectively. Clinical Considerations Disease-associated maternal and/or embryo/fetal risk Pregnant women with heart failure are at increased risk for preterm birth. Clinical classification of heart disease may worsen with pregnancy and lead to maternal or fetal death. Pregnant women with atrial fibrillation are at an increased risk of delivering a low birth weight infant. Atrial fibrillation may worsen with pregnancy and can lead to maternal or fetal death. Fetal/neonatal adverse reactions Digoxin has been shown to cross the placenta and is found in amniotic fluid. Monitor neonates for signs and symptoms of digoxin toxicity, including vomiting, and cardiac arrhythmias. Dose adjustments during pregnancy and the postpartum period Digoxin requirements may increase during pregnancy and decrease in the postpartum period. Monitor serum digoxin levels during pregnancy and the postpartum period. Labor or Delivery Risk of arrhythmias may increase during the labor and delivery. Monitor patients continuously during labor and delivery. 8.2 Lactation Risk Summary The digoxin dose received through breastfeeding is up to 4% of the neonatal maintenance dosage, which is unlikely to be clinically relevant. There are no data on the effects of digoxin on the breastfed infant or the effects on milk reduction. Data Based on data from two lactation studies in a total of 13 breastfed infants, the digoxin concentrations in breast milk were between 0.4 – 1.0 ng/mL following 0.25 mg once daily dose of digoxin in the lactating mother. Thus, the amount of digoxin ingested daily by the infants is estimated to be between 0.03 to 0.16 mcg/kg/day. This translates to a relative infant dose of digoxin between 1 to 7% of the maternal weight-adjusted dose and about 0.2 to 4% of the neonatal maintenance dose. 8.4 Pediatric Use Digoxin increases myocardial contractility in pediatric patients with congestive heart failure. There are no clinical efficacy studies demonstrating benefit in pediatric patients with heart failure. There are no controlled randomized studies of digoxin in pediatric patients with atrial tachyarrhythmias [see Clinical Studies (14.2) ] . 8.5 Geriatric Use The majority of clinical experience gained with digoxin has been in the elderly population. This experience has not identified differences in response or adverse effects between the elderly and younger patients. However, this drug is known to be substantially excreted by the kidney, and the risk of toxic reactions to this drug may be greater in patients with impaired renal function. Because elderly patients are more likely to have decreased renal function, care should be taken in dose selection, which should be based on renal function, and it may be useful to monitor renal function [see Dosage and Administration (2.4) ] . 8.6 …

12.1 Mechanism of Action All of digoxin’s actions are mediated through its effects on NaK–ATPase. This enzyme, the “sodium pump,” is responsible for maintaining the intracellular milieu throughout the body by moving sodium ions out of and potassium ions into cells. By inhibiting NaK–ATPase, digoxin • causes increased availability of intracellular calcium in the myocardium and conduction system, with consequent increased inotropy, increased automaticity, and reduced conduction velocity; • indirectly causes parasympathetic stimulation of the autonomic nervous system, with consequent effects on the sino-atrial (SA) and atrioventricular (AV) nodes; • reduces catecholamine reuptake at nerve terminals, rendering blood vessels more sensitive to endogenous or exogenous catecholamines; • increases baroreceptor sensitization, with consequent increased carotid sinus nerve activity and enhanced sympathetic withdrawal for any given increment in mean arterial pressure; • increases (at higher concentrations) sympathetic outflow from the central nervous system (CNS) to both cardiac and peripheral sympathetic nerves; and • allows (at higher concentrations) progressive efflux of intracellular potassium, with consequent increase in serum potassium levels. The cardiologic consequences of these direct and indirect effects are an increase in the force and velocity of myocardial systolic contraction (positive inotropic action), a slowing of the heart rate (negative chronotropic effect), and decreased conduction velocity through the AV node, and a decrease in the degree of activation of the sympathetic nervous system and renin-angiotensin system (neurohormonal deactivating effect).

11 DESCRIPTION Digoxin is one of the cardiac glycosides, a closely-related group of plant-derived drugs with shared pharmacological effects. The term "digitalis" is used to designate the whole group. Digoxin is extracted from the leaves of the common foxglove, Digitalis lanata . Like each of the other cardiac glycosides, digoxin consists of a polycyclic core and a sugar side chain. Digoxin’s chemical name is 3β-[O-2,6-dideoxy-β-D-ribo-hexopyranosyl-(1→4)-O-2,6-dideoxy-β-D-ribo-hexopyranosyl-(1→4)-2,6-dideoxy-β-D-ribo-hexopyranosyl)oxy]-12β,14-dihydroxy-5β-card-20(22)-enolide; its structural formula is: Its molecular formula is C 41 H 64 O 14 , and its molecular weight is 780.94. Digoxin is practically insoluble in water and in ether, slightly soluble in 50% ethanol and in chloroform, and freely soluble in pyridine. Digoxin, USP is a white or almost white powder, or colorless crystals. Digoxin Oral Solution, USP is formulated for oral administration. Each mL contains 50 mcg digoxin. The lime-flavored solution contains the following inactive ingredients: alcohol 10% (by volume at 60°F), glycerin, lime (imitation), methylparaben 0.1%, propylparaben 0.02%, purified water, sodium citrate and sorbitol solution. digoxin-chemical-structure-08.23.2023.jpg

10 OVERDOSAGE 10.1 Clinical Manifestations In adults, the signs and symptoms of toxicity are similar to those described in Adverse Reactions (6) but may be more frequent and severe. The most common signs and symptoms of digoxin toxicity are nausea, vomiting, anorexia, and fatigue that occur in 30% to 70% of patients who are overdosed. Extremely high serum concentrations produce hyperkalemia especially in patients with impaired renal function. Almost every type of cardiac arrhythmia has been associated with digoxin overdose and multiple rhythm disturbances in the same patient are common. Peak cardiac effects occur 3 to 6 hours following ingestion and may persist for 24 hours or longer. Arrhythmias that are considered more characteristic of digoxin toxicity are new-onset Mobitz type 1 A-V block, accelerated junctional rhythms, non-paroxysmal atrial tachycardia with A-V block, and bi-directional ventricular tachycardia. Cardiac arrest from asystole or ventricular fibrillation is usually fatal. Digoxin toxicity is related to serum concentration. As serum levels increase above 1.2 ng/mL, there is a potential for increase in adverse events. The effect on adverse events is enhanced by lower potassium levels. In adults with heart disease, clinical observations suggest that an overdose of digoxin of 10 to 15 mg results in death of half of patients. A dose above 25 mg ingested by an adult without heart disease appeared to be uniformly fatal if no Digoxin Immune Fab (DIGIBIND ® , DIGIFAB ® ) was administered. In pediatric patients, signs and symptoms of toxicity can occur during or shortly after the dose of digoxin. Frequent non-cardiac effects are similar to those observed in adults although nausea and vomiting are not seen frequently in infants and small pediatric patients. Other reported manifestations of overdose are weight loss in older age groups, failure to thrive in infants, abdominal pain caused by mesenteric artery ischemia, drowsiness, and behavioral disturbances including psychotic episodes. Arrhythmias and combinations of arrhythmias that occur in adult patients can also occur in pediatric patients although sinus tachycardia, supraventricular tachycardia, and rapid atrial fibrillation are seen less frequently in pediatric patients. Pediatric patients are more likely to develop A-V conduction disturbances, or sinus bradycardia. Any arrhythmia in a child treated with digoxin should be considered related to digoxin until otherwise ruled out. In pediatric patients aged 1 to 3 years without heart disease, clinical observations suggest that an overdose of digoxin of 6 to 10 mg would result in death of half of the patients. In the same population, a dose above 10 mg resulted in death if no Digoxin Immune Fab (DIGIBIND ® , DIGIFAB ® ) was administered. 10.2 Management of Toxicity Chronic Overdose If there is suspicion of toxicity, digoxin should be discontinued and the patient placed on a cardiac monitor. Contributing factors such as electrolyte abnormalities, thyroid dysfunction, and concomitant medications should be corrected [see Dosage and Administration (2.5) ] . Hypokalemia should be corrected by administering potassium so that serum potassium is maintained between 4.0 and 5.5 mmol/L. Potassium is usually administered orally, but when correction of the arrhythmia is urgent and serum potassium concentration is low, potassium may be administered cautiously by the intravenous route. The electrocardiogram should be monitored for any evidence of potassium toxicity (e.g. peaking of T waves) and to observe the effect on the arrhythmia. Potassium salts should be avoided in patients with bradycardia or heart block. Symptomatic arrhythmias may be treated with Digoxin Immune Fab (DIGIBIND ® , DIGIFAB ® ). Acute Overdose Patients who have intentionally or accidently ingested massive doses of digoxin should receive activated charcoal orally or by nasogastric tube regardless of the time since ingestion since digoxin recirculates to the inte …

16 HOW SUPPLIED/STORAGE AND HANDLING Digoxin Oral Solution, USP 50 mcg per 1 mL is supplied as a (lime-flavored) clear, colorless solution. NDC 0054-0057-46: Bottle of 60 mL with a calibrated oral syringe Storage Store at 20° to 25°C (68° to 77°F). [See USP Controlled Room Temperature.] Protect from light.