Skip to Content

Antithymocyte Globulin (Equine)

Class: Immunosuppressive Agents
- Antilymphocyte Immunoglobulins
- Immunosuppressive Agents
ATC Class: L04AA04
VA Class: IM600
Brands: Atgam

Medically reviewed by Drugs.com on Jan 27, 2020. Written by ASHP.

Warning

  • Should be used only by clinicians experienced in immunosuppressive therapy for the management of renal transplant or aplastic anemia patients.

  • Patients receiving antithymocyte globulin (equine) should be treated in facilities equipped and staffed with adequate laboratory and supportive medical resources.

Introduction

Lymphocyte immune globulin, antithymocyte globulin (equine) (ATG [equine]); equine-derived polyclonal antibody preparation; immunosuppressive agent.

Uses for Antithymocyte Globulin (Equine)

Renal Allotransplantation

Treatment of acute rejection of renal allografts, usually in conjunction with other immunosuppressive therapy.

Adjunctive ATG (equine) therapy successfully reverses most initial episodes of acute rejection in renal allograft recipients, including a high percentage of episodes severe enough to require hemodialysis.

Also may be effective for recurrent episodes of acute rejection and acute rejection episodes unresponsive to high-dose corticosteroid therapy.

ATG (equine) found to be less effective than antithymocyte globulin (rabbit) in reversing acute rejection episodes (76% compared with 88%) and preventing recurrent rejection episodes in renal transplant recipients.

Also used as induction therapy in conjunction with other immunosuppressive therapy to prevent or delay onset of renal allograft rejection. However, improved graft survival has not been consistently demonstrated.

Aplastic Anemia

Treatment of moderate to severe aplastic anemia in patients unsuitable for bone marrow transplantation.

When combined with conventional supportive therapy in patients with aplastic anemia, ATG (equine) may induce a partial or complete hematologic remission.

Safety and efficacy not fully evaluated in patients with aplastic anemia who are suitable candidates for bone marrow transplantation or in those with aplastic anemia secondary to neoplastic disease, storage disease, myelofibrosis, Fanconi's syndrome, or exposure to myelotoxic agents or radiation.

Graft-versus-host Disease

Treatment of corticosteroid-refractory and/or moderate to severe acute graft-versus-host disease (GVHD) following allogeneic hematopoietic stem cell transplantation or bone marrow transplantation.

Also has been used for the prevention of GVHD following bone marrow transplantation.

Other Organ Transplants

Has been used with some success to prevent and/or manage cardiac allograft rejection in combination with other immunosuppressive medications.

Also has been used for induction therapy or treatment of rejection in lung transplantation and combined heart-lung transplantation.

Has been used in skin allotransplantation.

Pure Red Cell Aplasia

Has been used for treatment of pure red cell aplasia (PRCA) in some patients refractory to other therapies.

Antithymocyte Globulin (Equine) Dosage and Administration

General

Usually administered in conjunction with other immunosuppressive agents (e.g., azathioprine and corticosteroids).

Intradermal Sensitivity Testing

  • Because of risk of severe systemic reaction (e.g., anaphylaxis), intradermal sensitivity testing is recommended in all individuals prior to administration of initial ATG (equine) dose.

  • Skin test procedure: Inject intradermally 0.1 mL of a 1:1000 dilution of ATG (equine) concentrate for injection in 0.9% sodium chloride (5 mcg of equine IgG); only use fresh diluted ATG (equine). Administer control test of 0.9% sodium chloride injection contralaterally to facilitate interpretation of results.

  • Observe patient and skin test site every 15–20 minutes during the first hour after intradermal injection of drug for positive reaction (wheal and/or area of erythema ≥10 mm in diameter, with or without pseudopod formation, and itching or marked local swelling) and question patient about occurrence of systemic manifestations.

  • If intradermal skin test is positive, seriously consider alternative forms of therapy and weigh risk of administration against risk of withholding ATG (equine). If therapy considered appropriate following a positive skin test reaction, administer drug only in a setting in which facilities for intensive life support are immediately available and where a clinician familiar with management of potentially life-threatening allergic reactions is in attendance.

    A systemic reaction to the skin test (e.g., generalized rash, tachycardia, dyspnea, hypotension, anaphylaxis) usually precludes further ATG (equine) administration. (See Contraindications under Cautions.)

  • Predictive value of skin test procedure not proven clinically; allergic reactions, including anaphylaxis, have occurred in patients whose skin test was negative. Always take precautions to treat severe systemic reactions.

Premedication

  • To minimize or prevent infusion-related adverse effects (including fever and chills), the manufacturer and some clinicians recommend premedication with an antipyretic (e.g., acetaminophen), antihistamine (e.g., diphenhydramine), or corticosteroids or some combination of these agents prior to ATG (equine) infusion.

Prophylactic Antiviral Therapy

  • Although not specifically recommended by manufacturer, some clinicians administer prophylactic antiviral therapy (e.g., acyclovir, ganciclovir, valganciclovir) during ATG (equine) therapy. (See Immunosuppressive-related Infectious Complications and Hematologic Effects under Cautions.)

Administration

IV Administration

For solution compatibility information, see Stability.

Administer ATG (equine) by slow IV infusion. Allow to reach room temperature prior to administration.

Because slight granular or flaky deposits may develop in ATG (equine) concentrate for injection during storage, the manufacturer states that ATG (equine) solutions should be infused through an inline 0.2- to 1-µm filter.

Administer into a high-flow central vein, vascular shunt, or arteriovenous fistula (e.g., Brescia-Cimino fistula) to minimize risk of phlebitis and thrombosis.

Dilution

ATG (equine) concentrate for injection must be diluted prior to IV infusion.

Dilute appropriate dose of ATG (equine) concentrate for injection in 0.9% sodium chloride injection, 5% dextrose and 0.225% sodium chloride injection, or 5% dextrose and 0.45% sodium chloride injection (usually 250–1000 mL); final concentration preferably should not provide >4 mg of equine IgG per mL.

Invert IV infusion solution container into which ATG (equine) is added to prevent contact of undiluted ATG (equine) with air inside container. Mix diluted solution by gently rotating or swirling container; do not shake.

Rate of Administration

Infuse the appropriate dose over at least 4 hours (usually 4–8 hours).

Dosage

Dosage of ATG (equine) is expressed in terms of equine IgG.

Some clinicians have monitored peripheral blood levels of rosette-forming cells (RFCs) during ATG (equine) therapy in allograft recipients to determine the degree of immunosuppression attained and guide dosage adjustment, with ATG (equine) dosage adjusted to maintain RFC level at about 10% of the pretreatment level, while other clinicians have questioned the reliability and value of this method. The availability of monoclonal antibodies has allowed monitoring of specific T-cell subsets, and some clinicians previously have monitored peripheral blood levels of OKT3-reactive cells as a method for guiding dosage adjustment, with ATG (equine) dosage adjusted to maintain the level of OKT3-reactive cells at about 10% of the pretreatment value. Monitoring of CD3 T cells currently is used by some clinicians to guide ATG (equine) dosage adjustment and reduce risk of immunosuppression and treatment costs.

Pediatric Patients

Renal Allotransplantation
Prevention of Renal Allograft Rejection (Induction Therapy)
IV Infusion

15 mg/kg daily for 14 days followed by 15 mg/kg every other day for an additional 14 days (total of 21 doses in 28 days). Usually continue other immunosuppressive therapies used for prevention and/or treatment of renal transplant rejection (e.g., azathioprine, corticosteroids, graft irradiation). (See Interactions.)

First dose given within 24 hours before or after transplantation.

Treatment of Acute Renal Allograft Rejection
IV Infusion

10–15 mg/kg daily for 14 days; if necessary, may be followed by 10–15 mg/kg every other day for an additional 14 days (total of 21 doses in 28 days). Usually continue other immunosuppressive therapies used for prevention and/or treatment of renal transplant rejection (e.g., azathioprine, corticosteroids, graft irradiation). (See Interactions.)

First dose given when initial episode of acute rejection is diagnosed.

Aplastic Anemia
Treatment of Aplastic Anemia
IV Infusion

10–20 mg/kg daily for 8–14 consecutive days, followed by 10–20 mg/kg every other day for up to an additional 14 days if necessary (up to a total of 21 doses in 28 days).

Prophylactic platelet transfusions may be necessary to maintain platelet counts at clinically acceptable levels because thrombocytopenia may occur in aplastic anemia patients receiving ATG (equine) therapy.

Graft-versus-host Disease†
Treatment of Acute GVHD†
IV Infusion

Optimum dosage not established; various dosage regimens including 5–15 mg/kg daily, 15–30 mg/kg every other day, and 15 mg/kg twice daily have been given for at least 1–10 doses in adult and pediatric patients.

Adults

Renal Allotransplantation
Prevention of Renal Allograft Rejection (Induction Therapy)
IV Infusion

15 mg/kg daily for 14 days followed by 15 mg/kg every other day for an additional 14 days (total of 21 doses in 28 days). Usually continue other immunosuppressive therapies used for prevention and/or treatment of renal transplant rejection (e.g., azathioprine, corticosteroids, graft irradiation). (See Interactions.)

First dose given within 24 hours before or after transplantation.

Treatment of Acute Renal Allograft Rejection
IV Infusion

10–15 mg/kg daily for 14 days; may be followed by 10–15 mg/kg every other day for another 14 days (total of 21 doses in 28 days). Usually continue other immunosuppressive therapies used for prevention and/or treatment of renal transplant rejection (e.g., azathioprine, corticosteroids, graft irradiation). (See Interactions.)

First dose given when initial acute rejection episode diagnosed.

Aplastic Anemia
Treatment of Aplastic Anemia
IV Infusion

10–20 mg/kg daily for 8–14 consecutive days, followed by 10–20 mg/kg every other day for up to an additional 14 days if necessary (up to a total of 21 doses in 28 days).

Prophylactic platelet transfusions may be necessary to maintain platelet counts at clinically acceptable levels because thrombocytopenia may occur in aplastic anemia patients receiving ATG (equine) therapy.

GVHD†
Treatment of Acute GVHD†
IV Infusion

Optimum dosage not established; various dosage regimens including 5–15 mg/kg daily, 15–30 mg/kg every other day, and 15 mg/kg twice daily have been given for at least 1–10 doses in adult and pediatric patients.

Prevention of Acute GVHD†
IV Infusion

Optimum dosage not established; 7 or 10 mg/kg every other day for 6 doses has been given.

Prescribing Limits

Adults

Renal Allotransplantation
Prevention and Treatment of Renal Allograft Rejection
IV infusion

Not determined; manufacturer states that some patients have received up to 50 doses of ATG (equine) (10–20 mg/kg per dose) in 4 months and others have received 28-day courses of 21 doses followed by up to 3 additional courses.

Special Populations

No special population dosage recommendations at this time.

Cautions for Antithymocyte Globulin (Equine)

Contraindications

  • Severe systemic reaction during prior ATG (equine) administration or to any other equine immunoglobulin G preparation.

Warnings/Precautions

Warnings

For information regarding supervising clinicians and treatment facilities, see Boxed Warning.

Lot Variability in Activity

Precise methods for determining the potency of ATG (equine) not established; activity may vary from lot to lot.

Discontinuance of Therapy for Severe Adverse Reactions

Immediately discontinue ATG (equine) and give appropriate therapy if anaphylaxis or signs or symptoms suggesting potential anaphylaxis (e.g., hypotension, respiratory distress, or pain in the chest, flank, or back) occur. (See Intradermal Sensitivity Testing under Dosage and Administration and see Anaphylaxis under Cautions.)

Discontinue ATG (equine) if severe and unremitting thrombocytopenia and/or leukopenia occurs in renal transplant patients.

Risk of Infectious Agent Transmission

Because ATG (equine) is made using equine and human blood components, possible risk of transmitting infectious agents (e.g., viruses and, theoretically, the Creutzfeldt-Jakob disease [CJD] agent).

Sensitivity Reactions

Anaphylaxis

Anaphylaxis (which may be manifested as hypotension, respiratory distress, or pain in the chest, flank, or back) reported in <1% of patients.

Because of the risk of severe systemic reaction (including anaphylaxis) to ATG (equine), intradermal sensitivity testing is recommended in all individuals prior to administration of initial ATG (equine) dose. (See Intradermal Sensitivity Testing under Dosage and Administration.)

If anaphylaxis or any of these other symptoms occurs, immediately discontinue the ATG (equine) infusion and initiate appropriate therapy (e.g., epinephrine, corticosteroids, maintenance of an adequate airway, oxygen, IV fluids, antihistamines, maintenance of BP).

Patients with a history of anaphylaxis to ATG (equine) should not receive the drug again.

General Precautions

Intradermal sensitivity testing strongly recommended prior to IV infusion of ATG (equine). (See Intradermal Sensitivity Testing under Dosage and Administration and see Anaphylaxis under Cautions.)

Manufacturer states that safety and efficacy of ATG (equine) demonstrated only in renal transplant patients who received concomitant immunosuppressive therapy and in patients with aplastic anemia.

Immunosuppressive-related Infectious Complications and Hematologic Effects

Because ATG (equine) is an immunosuppressive agent and ordinarily is combined with other immunosuppressive therapy (e.g., corticosteroids, azathioprine), carefully observe patients for signs of leukopenia, thrombocytopenia, and/or concurrent infection during therapy.

An increased incidence of cytomegalovirus (CMV) infection has been reported in several studies; results of 1 study suggest possible reduced risk if lower dosages of other immunosuppressive agents are concurrently administered with ATG (equine). (See Prophylactic Antiviral Therapy under Dosage and Administration and see Specific Drugs under Interactions.) If infection occurs, promptly initiate appropriate therapy; clinician should decide based on clinical circumstances whether to discontinue ATG (equine) therapy.

Specific Populations

Pregnancy

Category C. National Transplantation Pregnancy Registry at 877-955-6877.

Lactation

Not known whether ATG (equine) is distributed into milk, but may be distributed into milk since immunoglobulins (e.g., IgA, IgM, IgG) are present in colostrum. Use with caution.

Pediatric Use

The manufacturer states that experience in children is limited. However, ATG (equine) has been administered safely to some pediatric renal allograft recipients and aplastic anemia patients without unusual adverse effects. ATG (equine) has also been used in the treatment of acute GVHD in pediatric patients following allogeneic hematopoietic stem cell transplantation or bone marrow allotransplantation. (See Graft-versus-host Disease under Uses.)

Common Adverse Effects

Renal allotransplantation: Fever, chills, leukopenia, thrombocytopenia, dermatologic reactions (rash, pruritus, urticaria, wheal and flare).

Aplastic anemia: Fever, chills, skin reactions, arthralgia, headache, myalgia, nausea, chest pain, phlebitis, serum sickness.

Interactions for Antithymocyte Globulin (Equine)

Specific Drugs

Drug

Interaction

Comments

Basiliximab

No increase in adverse effects

Immunosuppressive agents

Risk of oversuppression of the immune system and associated susceptibility to infection and malignancies, including lymphoma and lymphoproliferative disorders

Consider decreasing maintenance immunosuppressive therapy during concurrent administration

Antithymocyte Globulin (Equine) Pharmacokinetics

Absorption

Onset

Immediate reduction in rosette-forming cell (RFC) levels in peripheral blood occurs following IV administration of ATG (equine); time for RFCs to recover to normal levels after drug discontinuance depends on the patient’s catabolic rate and, in some patients, duration of therapy.

Plasma Concentrations

Peak plasma levels of equine IgG vary following IV administration of ATG (equine) depending on the patient’s ability to catabolize foreign IgG. Mean peak plasma concentrations of equine IgG averaged 727 ± 310 mcg/mL after IV infusion of ATG (equine) 10 mg/kg daily for 5 days.

Distribution

Extent

Not fully characterized.

ATG (equine) is likely to be poorly distributed into lymphoid tissues (e.g., spleen, lymph nodes), since antilymphocyte serum poorly distributes into these tissues.

In vitro, ATG (equine) binds to essentially all circulating lymphocytes, granulocytes, and platelets; bone marrow cells; visceral tissues, including thymus and testis cell membranes, and to nuclear and cytoplasmic components of tonsil, kidney, breast, liver, lung, intestine, and testes (including Leydig cells).

Not known whether ATG (equine) crosses placenta, but placental distribution likely since other immunoglobulins cross placenta; virtually all transplacental passage of immunoglobulins occurs during the last 4 weeks of pregnancy.

Not known whether ATG (equine) distributes into human milk; however, may be distributed into milk since other immunoglobulins (e.g., IgA, IgM, IgG) are present in colostrum.

Elimination

Elimination Route

Approximately 1% excreted in urine, principally as unchanged equine IgG.

Half-life

Plasma half-life averages about 6 days (1.5–12 days).

Stability

Storage

Parenteral

Concentrate for Injection

2–8°C; do not freeze.

Store diluted solutions at 2–8°C; use within 24 hours of dilution (including actual infusion time).

Solutions for IV infusion containing <4 mg/mL prepared using 0.9% sodium chloride injection, 5% dextrose and 0.225% sodium chloride injection, or 5% dextrose and 0.45% sodium chloride injection are stable for up to 24 hours.

Dextrose injection should not be used as a diluent for antithymocyte globulin (equine) solution.

Highly acid infusion solutions should not be used as a diluent for antithymocyte globulin (equine) solution.

Although reconstituted solutions are physically and chemically stable at room temperature for up to 24 hours, room temperature storage is not recommended by the manufacturer since the preparation contains no preservatives; use immediately.

Use diluted solutions immediately.

Actions

  • Equine-derived polyclonal antibody immunosuppressive agent.

  • Exact mechanism of immunosuppressive action not fully elucidated; appears to involve clearance of peripheral antigen-reactive T lymphocytes (T cells) and/or alteration of T-cell function.

    Exact mechanism of hematologic effects variable, complex, and not fully elucidated. In vitro studies indicate ATG (equine) essentially binds to all circulating lymphocytes (both T and B cells), granulocytes, and platelets. May produce leukopenia, thrombocytopenia, and/or hemolysis. Also produces a hematopoietic response in some patients with aplastic anemia.

    Appears to have some antineoplastic activity against malignant lymphomas.

Advice to Patients

  • Importance of informing patients about the potential benefits of ATG (equine) and attendant risks of immunosuppressive therapy.

  • Risk of decreased number of WBCs (including lymphocytes), which could increase risk of infection; less commonly, anemia and hemolysis also may occur. Necessity of administration under supervision of a clinician with careful monitoring for signs of reduced WBC and platelet counts. Importance of informing clinicians promptly if any signs or symptoms of infection occur.

  • Advise patient of risk of possible fever, chills, allergic reactions, malaise, arthralgia, nausea and vomiting, lymphadenopathy, and/or rash during or following ATG (equine) infusion and that medication will be given to help control these reactions.

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

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

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

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.

Antithymocyte Globulin (Equine)

Routes

Dosage Forms

Strengths

Brand Names

Manufacturer

Parenteral

For injection, concentrate, for IV use only

50 mg of equine IgG per mL

Atgam (with glycine)

Pfizer

AHFS DI Essentials™. © Copyright 2021, Selected Revisions January 27, 2020. American Society of Health-System Pharmacists, Inc., 4500 East-West Highway, Suite 900, Bethesda, Maryland 20814.

† Use is not currently included in the labeling approved by the US Food and Drug Administration.

Show article references

More about lymphocyte immune globulin, anti-thy (equine)

Consumer resources

Professional resources

Other brands
Atgam

Related treatment guides