Digoxin Immune Fab (Ovine) (Monograph)

Brand name: DigiFab
Drug class: Antitoxins and Immune Globulins

Medically reviewed by Drugs.com on Jun 10, 2024. Written by ASHP.

Introduction

Antidote for digoxin toxicity; ovine immunoglobulin Fab fragments capable of binding digoxin.^{1 2 3 4 5 6 7 20}

Uses for Digoxin Immune Fab (Ovine)

Digoxin Toxicity

Treatment of life-threatening or potentially life-threatening digoxin toxicity or overdosage;^{1 82 83 84 85 87 120 127} designated an orphan drug by FDA for treatment of potentially life-threatening cardiac glycoside intoxication refractory to conventional management.⁶²

Has been used for treatment of life-threatening overdosage of digitoxin^{† [off-label]1 82} or lanatoside C^{† [off-label]49} (cardiac glycosides not commercially available in US).

Indicated in acute digoxin ingestions (e.g., known suicidal or accidental consumption) of ≥10 mg of digoxin in previously healthy adults or ≥4 mg (or >0.1 mg/kg) of digoxin in previously healthy children.¹ Minimum toxic or lethal acute doses of digoxin not well established;⁵⁶ acute digoxin ingestions of >10 mg in previously healthy adults or >4 mg in previously healthy children often result in cardiac arrest.^{68 74}

Indicated in acute digoxin ingestions resulting in steady-state serum digoxin concentrations ≥10 ng/mL or chronic ingestions resulting in steady-state serum digoxin concentrations >6 ng/mL in adults or >4 ng/mL in children.¹

Indicated when there are manifestations of life-threatening digoxin toxicity, including severe ventricular arrhythmias, progressive bradycardia (e.g., second- or third-degree heart block not responsive to atropine), or serum potassium concentrations >5.5 mEq/L in adults or >6 mEq/L in children with rapidly progressive signs and symptoms of digoxin toxicity.¹

Progressive hyperkalemia treated by conventional supportive and symptomatic measures without digoxin immune Fab (ovine) has poor prognosis.^{6 40 45 46 47 68} Also consider other potential causes of hyperkalemia, especially if digoxin immune Fab (ovine) does not appear to substantially decrease serum potassium concentrations.⁶⁹

Poisonings Involving Cardiotoxic Plants and Other Substances

Has been used for treatment of poisonings involving ingestion of certain cardiotoxic plants, including common or pink oleander^{† [off-label]} (Nerium oleander),^{79 87 92} yellow oleander^{† [off-label]} (Thevetia peruviana),^{87 89 90 95 125} Indian hemp^{† [off-label]} (Apocynum cannabinum),⁸⁷ and foxglove^† (Digitalis purpurea).^{122 126} Has reversed or improved cardiotoxicity in some individuals;^{79 87 89 90 95 122} additional study needed.^{92 95}

Has reversed or improved cardiotoxicity associated with ingestion of toad venom^† in a few patients.^{94 123} Toad venom contains several cardioactive steroids (bufadienolides), including bufalin, cinobufagin, cinobufotalin, and resibufogenin, and has been identified in illicit street drugs marketed as aphrodisiacs.^{87 94 123 124}

Preeclampsia and Eclampsia

Has been used with some success for management of severe preeclampsia^† or eclampsia^†;^{109 110 111 112 116 121} designated an orphan drug by FDA for treatment of severe preeclampsia and eclampsia.⁶²

Severe preeclampsia and eclampsia are major causes of maternal and fetal morbidity and mortality.^{109 110 111 112 113 115 116 118 121} There is some evidence that increased concentrations of endogenous cardiotonic steroids, including endogenous digitalis-like factors (EDLFs), in maternal and/or cord blood may contribute to pathogenesis of preeclampsia, particularly elevated BP;^{109 111 112 114 115 116 117 118 119 121} additional study needed to evaluate use of digoxin immune Fab (ovine).^{109 110 113 115 116}

Digoxin Immune Fab (Ovine) Dosage and Administration

Administration

IV Administration

Administer by IV infusion.^{1 2 3 6 20}

Manufacturer states may be given by rapid IV injection if cardiac arrest is imminent;¹ however, rapid administration may be associated with increased risk of infusion reactions or other adverse effects (e.g., allergic reactions)¹ and not generally recommended.⁶⁹

Reconstitution and Dilution

Add 4 mL of sterile water for injection to vial containing 40 mg of digoxin immune Fab (ovine) to provide solution containing approximately 10 mg/mL;¹ gently mix until dissolved.¹

Do not use if reconstituted solution appears cloudy, turbid, or contains particulates.¹

For IV infusion, reconstituted solution may be diluted to an appropriate volume with 0.9% sodium chloride injection.¹

Infants or small children (<20 kg) receiving a small dose (<1 mL): Reconstituted solution may be given undiluted by IV injection using a tuberculin syringe.¹ Alternatively, for very small doses (≤3 mg), reconstituted solution can be diluted with 36 mL of 0.9% sodium chloride injection to provide solution containing 1 mg/mL.¹

Rate of Administration

Administer by IV infusion over at least 30 minutes.^{1 3 6 20}

Slower IV infusion rates have been used (e.g., over 1–5 hours),^{2 20 32 49 69 73 82} but do not appear to offer any advantage and may delay response.^{49 69}

May be given by rapid IV injection if cardiac arrest is imminent.^{1 6}

Dosage

Dosage of digoxin immune Fab (ovine) varies according to amount of digoxin to be neutralized.^{1 2 3 6 20 120}

Digoxin immune Fab (ovine) is commercially available in the US as DigiFab.¹ Although a different preparation of digoxin immune Fab (ovine) also was previously available (Digibind) and product-specific dosage recommendations were required,⁴⁴ this other preparation is no longer commercially available in the US.

The contents of one 40-mg vial of DigiFab neutralizes approximately 0.5 mg of digoxin.¹

Usually given as a single dose.¹ If toxicity not adequately reversed several hours after the dose or if toxicity recurs, an additional dose may be necessary;^{1 120} use clinical judgment to guide dose selection.¹

When amount of digoxin ingested is unknown and cannot be estimated and when serum digoxin concentrations are unavailable, general dosing guidelines can be used and may be adequate to treat most life-threatening digoxin overdosages.¹

If amount of digoxin ingested is known, dose required to neutralize the cardiac glycoside can be calculated using estimated total body load (TBL) of digoxin, which takes into consideration amount (mg of digoxin) and bioavailability of digoxin preparation ingested.¹ Alternatively, dose can be calculated based on steady-state serum digoxin concentrations.¹

When a calculated dose is used, consider that an inaccurate estimate of amount of digoxin ingested or absorbed may occur if serum digoxin concentrations were not measured at steady state or were outside measurable limits of assay used (digoxin assay kits are designed to measure serum concentrations <5 ng/mL; dilution of serum sample required to accurately measure concentrations >5 ng/mL).¹

Also consider that an average steady-state volume of distribution of digoxin (5 L/kg) is used to convert serum digoxin concentrations to TBL of digoxin in mg; however, volume of distribution of the drug may vary widely among individuals.^{1 69} Many patients may require a higher dose for complete neutralization, and doses should be rounded up to the nearest whole vial.¹

If dose of digoxin immune Fab (ovine) estimated based on the acute ingested dose of digoxin differs substantially from dose calculated using serum digoxin concentration, it may be preferable to use the higher dose.¹

If there is no response to an adequate dose of digoxin immune fab (ovine), consider possibility that clinical problem is not caused by digoxin intoxication and re-evaluate diagnosis.¹

Pediatric Patients

General Dosing for Digoxin Toxicity

Toxicity Following Acute Ingestion of Unknown Digoxin Amount When Serum Digoxin Concentrations Unknown

IV

Children: 800 mg (twenty 40-mg vials) usually adequate for most life-threatening ingestions.¹ Monitor small children (<20 kg) for fluid overload.¹

Administer 400 mg (ten 40-mg vials) initially, observe patient's response, and then administer additional dose of 400 mg if clinically indicated.¹

Toxicity During Chronic Digoxin Therapy When Serum Digoxin Concentrations Unknown

IV

Children ≥20 kg: 240 mg (six 40-mg vials) usually sufficient.¹

Infants and small children (<20 kg): 40 mg (one 40-mg vial) usually sufficient.¹

Calculated Dose for Digoxin Toxicity

Toxicity Following Acute Ingestion of Known Digoxin Amount

IV

Dose may be calculated based on amount of digoxin ingested and estimated TBL, taking into consideration bioavailability of preparation ingested.¹ Digoxin tablets are 80% absorbed; digoxin liquid-filled capsules are 100% absorbed.¹

For digoxin tablets: TBL (in mg) = amount (in mg) ingested x 0.8.¹

For digoxin liquid-filled capsules or IV digoxin: TBL (in mg) = 100% of amount (in mg) ingested or infused (i.e., do not multiply by 0.8).^{1 68}

Since each vial binds approximately 0.5 mg of digoxin, dose (in number of vials) is calculated by dividing TBL (in mg) by 0.5.¹

Dose (in number of vials) = TBL (in mg) / 0.5 (mg of digoxin bound/vial)¹

Alternatively, for children who have ingested a single large digoxin dose (as 0.25-mg tablets or 0.2-mg liquid-filled capsules) and when approximate number of tablets or capsules ingested is known, approximate dose (in number of vials) can be estimated using Table 1.¹

Toxicity During Chronic Digoxin Therapy When Serum Digoxin Concentrations Known

IV

Infants and small children (<20 kg): Calculate dose as mg of digoxin immune Fab (ovine), not as number of vials.¹

Calculate dose (in number of vials) based on steady-state serum digoxin concentrations by multiplying serum digoxin concentration (in ng/mL) by patient's weight (kg) and dividing by 100.¹

Dose (in number of vials) = [Conc of digoxin (in ng/mL) × body weight (in kg)]/100

Calculate dose (in mg) by multiplying the dose (in number of vials) by 40 mg/vial.¹

Dose (in mg) = [Conc of digoxin (in ng/mL) × body weight (in kg) × 40 mg/vial]/100

Alternatively, for infants and small children (<20 kg), dose (in mg) can be estimated based on patient's weight and steady-state serum digoxin concentrations (see Table 2).¹

Adults

General Dosing for Digoxin Toxicity

Toxicity Following Acute Ingestion of Unknown Digoxin Amount When Serum Digoxin Concentrations Unknown

IV

800 mg (twenty 40-mg vials) usually adequate for most life-threatening ingestions.¹

Administer 400 mg (ten 40-mg vials) initially, observe patient's response, and then administer additional dose of 400 mg if clinically indicated.¹

Toxicity During Chronic Therapy When Serum Digoxin Concentrations Unknown

IV

240 mg (six 40-mg vials) usually sufficient.¹

Calculated Dose for Digoxin Toxicity

Toxicity Following Acute Ingestion of Known Digoxin Amount

IV

Dose may be calculated based on amount of digoxin ingested and estimate of TBL, taking into consideration bioavailability of preparation ingested.¹ Digoxin tablets are 80% absorbed; digoxin liquid-filled capsules are 100% absorbed.¹

For digoxin tablets: TBL (in mg) = amount (in mg) ingested x 0.8.¹

For digoxin liquid-filled capsules or IV digoxin: TBL (in mg) = 100% of the amount (in mg) ingested or infused (i.e., do not multiply by 0.8).^{1 68}

Since each vial of digoxin immune Fab (ovine) binds approximately 0.5 mg of digoxin, dose (in number of vials) is calculated by dividing the TBL (in mg) by 0.5.¹

Dose (in number of vials) = TBL (in mg) / 0.5 (mg of digoxin bound/vial)

Alternatively, for adults who have ingested a single large digoxin dose (as 0.25-mg tablets or 0.2-mg liquid-filled capsules) and when approximate number of tablets or capsules ingested is known, approximate dose (in number of vials) can be estimated using Table 3.¹

Toxicity During Chronic Digoxin Therapy When Serum Digoxin Concentrations Known

IV

Calculate dose (in number of vials) based on steady-state serum digoxin concentrations by multiplying serum digoxin concentration (in ng/mL) by patient's weight (kg) and dividing by 100.¹

Dose (in number of vials) = [Conc of digoxin (in ng/mL) × body weight (in kg)]/100

Alternatively, dose (in mg) can be estimated based on patient's weight and steady-state serum digoxin concentrations (see Table 4).¹

Special Populations

Hepatic Impairment

No specific dosage recommendations.¹

Renal Impairment

No specific dosage recommendations.¹ (See Renal Impairment under Cautions.)

Geriatric Patients

No specific dosage recommendations.¹ (See Geriatric Use under Cautions.)

Cautions for Digoxin Immune Fab (Ovine)

Contraindications

• Manufacturer states none, but states do not use in patients with known hypersensitivity to papaya or papain unless benefits outweigh risks.¹ (See Papain Hypersensitivity under Cautions.)

Warnings/Precautions

Sensitivity Reactions

Consider possibility of hypersensitivity reactions (including anaphylaxis or anaphylactoid reactions), delayed allergic reactions, or febrile reactions.¹

Carefully monitor for signs and symptoms of acute allergic reaction (e.g., urticaria, pruritus, erythema, angioedema, bronchospasm with wheezing or cough, stridor, laryngeal edema, hypotension, tachycardia).¹ If allergic reaction occurs, immediately discontinue digoxin immune Fab (ovine) and initiate appropriate therapy (e.g., oxygen, volume expansion, diphenhydramine, corticosteroids, airway management).¹ Balance need for epinephrine against potential risk in the setting of digitalis toxicity.¹

Patients with known allergies (especially to sheep proteins) and those who have previously received intact ovine antibodies or ovine Fab are at greatest risk for sensitivity reactions.¹

Because digoxin immune Fab (ovine) lacks antigenic Fc fragment, it should be less immunogenic than intact immunoglobulin; however, additional clinical experience needed to fully determine immunogenic risk.^{2 3 4 5 6 17 20 25 51 63}

Papain Hypersensitivity

Papain is used in manufacturing process to cleave whole antibody into Fab fragments.¹

Individuals allergic to papain, chymopapain, other papaya extracts, or the pineapple enzyme bromelain may be at risk of hypersensitivity reactions to digoxin immune Fab (ovine).¹

Do not use in patients with history of hypersensitivity to papaya or papain unless benefits outweigh risks;¹ keep appropriate treatments for anaphylaxis readily available.¹

Human Anti-ovine Fab Antibodies

Patients may develop ovine Fab-specific antibodies after receiving digoxin immune Fab (ovine).¹

In patients retreated with digoxin immune Fab (ovine), a decrease in drug efficacy secondary to the presence of human antibodies against ovine Fab theoretically may occur.¹ However, there have been no clinical reports of reduction in binding or neutralization response.¹

Suicidal Digoxin Ingestion

Suicidal ingestion often involves multiple drugs; in patients with known or suspected suicidal ingestion of digoxin, consider toxic effects of other drugs, especially if toxicity is not reversed by digoxin immune Fab (ovine).¹

Cardiovascular Effects

Potential worsening of low cardiac output states and heart failure, possibly by decreasing effective inotropic concentrations of digoxin;^{1 3 6 7 26 30} causal relationship not established.⁶

May consider use of inotropic agents (e.g., dopamine or dobutamine) or vasodilators if cardiac output decreases during digoxin immune Fab (ovine) therapy;¹ use sympathomimetic drugs cautiously since they may exacerbate or precipitate cardiac glycoside-induced ventricular arrhythmias.^{24 28}

Patients with preexisting atrial fibrillation may develop a rapid ventricular response secondary to reversal of the effects of cardiac glycosides on the AV node.^{1 2 6}

Use with caution in patients with intrinsically poor cardiac function; deterioration may occur from withdrawal of the inotropic action of digoxin.¹

Monitor closely during and after administration of digoxin immune Fab; periodically monitor body temperature, BP, and ECG.¹

Do not attempt redigitalization until digoxin immune Fab (ovine) elimination is complete (i.e., several days in normal renal function and ≥1 week in patients with renal insufficiency).¹ (See Renal Impairment under Cautions.)

General Supportive Measures and Serum Digoxin Monitoring

Immediately discontinue cardiac glycoside; correct fluid and electrolyte disturbances (especially hyperkalemia), acid-base imbalances, and hypoxia.^{22 23 24 48} (See Cardiovascular Effects and also see Hypokalemia and Hyperkalemia under Cautions.)

Whenever possible, obtain serum digoxin concentrations prior to initiating digoxin immune Fab (ovine).^{1 2 5 6} Digoxin immune Fab (ovine) causes rapid rise in total serum digoxin concentration, consisting almost completely of the Fab-bound, pharmacologically inactive form of the glycoside.^{1 2 4 6 20} (See Specific Drugs and Laboratory Tests under Interactions.)

Hypokalemia and Hyperkalemia

Monitor serum potassium concentrations frequently during and after administration of digoxin immune Fab (ovine), especially during first several hours after the dose.^{1 2 37 120} Hypokalemia or hyperkalemia may develop rapidly.^{1 2 22 23 24 34 39 50 56 57 120}

Advanced cardiac glycoside toxicity can cause life-threatening hyperkalemia by increasing extracellular potassium and/or by inhibiting potassium movement into cells.^{1 6 29 45 46 47} May result in increased renal excretion of potassium; patient may appear hyperkalemic while having a total body deficit of potassium.¹ Digoxin immune Fab (ovine) reverses the effect of glycoside toxicity and potassium shifts back into the cells, resulting in decline in serum potassium concentrations and, potentially, hypokalemia.^{1 6 29 45}

Occasionally, may need to treat hypokalemia; however, treat cautiously since hyperkalemia may develop rapidly in advanced intoxication.^{1 2 22 23 24 50 56 57}

Specific Populations

Pregnancy

Animal reproduction studies not performed;¹ not known whether the immune Fab causes fetal harm when administered to pregnant women.¹

Use during pregnancy only when clearly needed.¹

Lactation

Not known whether digoxin immune Fab (ovine) is distributed into human milk.¹

Use with caution in nursing women and only if clearly needed.¹

Pediatric Use

Limited safety data.¹ Has been used in some infants and children without unusual adverse effects.^{1 3 6 20 23 31 33 35 36 38} Estimated pediatric dose is based on calculations for adult dose.¹

Geriatric Use

No overall differences in safety or efficacy relative to younger adults.¹

Use with caution due to greater frequency of decreased renal function.¹ Monitor renal function and observe for possible recurrence of toxicity.¹ (See Renal Impairment under Cautions.)

Renal Impairment

Use with caution; decreased clearance of Fab fragment-digoxin complex in renal dysfunction.^{1 6} Elimination half-life in patients with renal impairment not clearly defined.¹

Unclear if reintoxication could occur in severe renal failure following release of newly unbound digoxin into the blood.¹ Consider monitoring free (unbound) digoxin concentrations to detect reintoxication.¹

Monitor patients with renal impairment, especially functionally anephric patients, for prolonged period of time for possible recurrence of digitalis toxicity.^{1 97 101 104} (See Special Populations under Pharmacokinetics.)

Delay redigitalization until elimination of digoxin immune Fab (ovine) is complete; may require ≥1 week in patients with renal insufficiency.¹ (See Cardiovascular Effects under Cautions.)

Common Adverse Effects

Worsening of heart failure, hypokalemia, worsening of atrial fibrillation.¹

Drug Interactions

Specific Drugs and Laboratory Tests

Digoxin Immune Fab (Ovine) Pharmacokinetics

Absorption

Onset

Peak serum concentrations occur at completion of IV infusion.^{2 25}

Rapidly binds to serum glycoside; serum concentrations of free (unbound) glycoside decline to undetectable levels within several minutes following completion of IV infusion.^{5 6 20 22 42 43 71 73}

Improvement in signs and symptoms of cardiac glycoside toxicity generally apparent within 30 minutes after completion of IV infusion;^{3 6 37} however, onset of response is variable and may depend on infusion rate, dose, and other factors.^{6 68 69 73}

Cardiac rhythm (e.g., ventricular fibrillation, other severe arrhythmias) may stabilize in 0.5–13 hours after initial dose.^{1 20}

Reversal of cardiac glycoside toxicity, including hyperkalemia, often complete within 2–6 hours.^{6 17 34 37 39 68 69 72 73}

Duration

Serum concentrations of free (unbound) glycoside remain low for 8–12 hours after completion of IV infusion.^{6 20 68} Decline in free serum glycoside concentration correlates clinically to toxicity reversal.^{2 3 6 7 21 23 45}

Distribution

Extent

Rapidly distributes throughout the extracellular space, into both plasma and interstitial fluid.^{2 7 17 20 21 27} Intracellular distribution may occur; additional study needed.^{25 68 73}

Not known whether digoxin immune Fab (ovine) crosses the placenta or is distributed into human milk.¹

Elimination

Elimination Route

Excreted in urine via glomerular filtration, principally as the cardiac glycoside-Fab fragment complex in intoxicated patients.^{1 7 20 21 73}

Hemodialysis and peritoneal dialysis appear to have no effect or only very minimal effect on removal of digoxin-immune Fab (ovine).^{101 104 105}

Half-life

Biphasic; elimination half-life 14–20 hours.^{1 2 6 25 27 73}

Special Populations

Patients with renal impairment: Terminal elimination half-life reported to be 25–137 hours;^{97 101} half-life may be increased up to tenfold.¹

Stability

Storage

Parenteral

Powder for Injection

2–8°C.¹ Do not freeze.¹

Use immediately following reconstitution, but may refrigerate at 2–8°C for up to 4 hours.¹

Actions

• Monovalent, digoxin-specific antigen binding fragments (Fab) derived from antidigoxin antibodies^{1 2 3 4 5 7 8 9 10 20 51} obtained from serum of immunized sheep (ovine).^{1 2 3 4 8 9 10 20 68}

• Binds to free (unbound) digoxin intravascularly and in extracellular fluid;^{1 2 5 6 11 12 17 20 29 51 63 70 71} prevents and reverses pharmacologic and toxic effects of digoxin, including biochemical and cardiac effects.^{1 2 3 4 5 6 7 8 12 17 20 26 27 28 29 30 31 32 33 34 35 36 37 38 39 49 51 55 66 70 71}

• Reverses toxicity induced by digitoxin (no longer commercially available in US). ^{1 3 13 14 15 16 18 19 20}

• Binds to other digoxin derivatives (e.g., β-methyldigoxin, β-acetyldigoxin),^{31 32} some of the cardioactive metabolites of digoxin,⁷ and possibly some other cardiac glycosides (e.g., lanatoside C).⁴⁹

• May bind to oleander glycosides.^{67 68 69}

• In vitro studies indicate that digoxin immune Fab (ovine) may cross-react with and bind to endogenous cardiotonic steroids, including endogenous digitalis-like factors (EDLFs), identified in maternal and/or cord blood from women with preeclampsia.^{115 118}

Advice to Patients

• Advise patients of the possibility of anaphylactic reactions during and after infusion.¹

• Importance of informing clinicians of allergy history, including allergy to sheep proteins, papaya, papain, chymopapain, other papaya extracts, or the pineapple enzyme bromelain.¹

• Importance of informing clinicians of any previous exposure to antibodies or Fab fragments derived from sheep serum.¹

• Importance of immediately informing clinician if any signs and symptoms of delayed allergic reaction or serum sickness (e.g., rash, hives, itching) occur after hospital discharge.¹

• Importance of informing clinicians of existing or contemplated concomitant therapy, including prescription and OTC drugs, as well as any concomitant illnesses.¹

• Importance of women informing clinicians if they are or plan to become pregnant or plan to breast-feed.¹

• Importance of informing patients of other important precautionary information.¹ (See Cautions.)

Additional Information

The American Society of Health-System Pharmacists, Inc. represents that the information provided in the accompanying monograph was formulated with a reasonable standard of care, and in conformity with professional standards in the field. Readers are advised that decisions regarding use of drugs are complex medical decisions requiring the independent, informed decision of an appropriate health care professional, and that the information contained in the monograph is provided for informational purposes only. The manufacturer’s labeling should be consulted for more detailed information. The American Society of Health-System Pharmacists, Inc. does not endorse or recommend the use of any drug. The information contained in the monograph is not a substitute for medical care.

Preparations

Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.

Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.

Medical Disclaimer