Pronunciation: REB-low-zil
Generic name: luspatercept-aamt
Dosage form: single-dose vial for subcutaneous injection (25 mg, 75 mg)
Drug class: Miscellaneous erythropoiesis agents

Medically reviewed by Carmen Pope, BPharm. Last updated on Jun 27, 2025.

What is Reblozyl?

Reblozyl is used to treat transfusion-dependent anemia in adults with beta-thalassemia, myelodysplastic syndromes (MDS), myelodysplastic syndromes with ring sideroblasts (MDS-RS), or myelodysplastic/myeloproliferative neoplasms with ring sideroblasts and thrombocytosis (MDS/MPN-RS-T). It is administered as a subcutaneous injection by a healthcare provider once every 3 weeks.

Reblozyl works by specifically targeting and blocking molecules that prevent red blood cells (RBCs) from maturing, allowing them to mature properly. This helps overcome ineffective erythropoiesis (the development of RBCs) seen in conditions such as beta-thalassemia and myelodysplastic syndromes, increasing the number of RBCs in the plasma and reducing the need for blood transfusions. Reblozyl belongs to the drug class called erythroid maturation agents.

Reblozyl (luspatercept-aamt) gained FDA approval on November 8, 2019. There is no generic or biosimilar. Approval for Reblozyl was based on the following clinical trials:

• Beta Thalassemia: BELIEVE (NCT02604433). Primary endpoint: 21.4% of Reblozyl patients achieved ≥33% transfusion reduction versus 4.5% placebo (P<0.0001). Secondary endpoints showed sustained benefits at weeks 37-48 (19.6% vs 3.6%) and ≥50% reduction in 7.6% vs 1.8% patients.
• Very Low, Low, or Intermediate Risk Myelodysplastic Syndromes: MEDALIST (NCT02631070). 38% Reblozyl patients achieved ≥8 weeks of transfusion independence versus 13% placebo (P<0.001). COMMANDS (NCT03682536). Interim analysis: Primary endpoint (≥1.5g/dL hemoglobin increase plus ≥12 weeks transfusion independence): 59% luspatercept versus 31% epoetin alfa (p<0.0001).

FDA approvals and uses

Reblozyl is approved to treat: 

• Anemia in adults with beta-thalassemia, who need regular red blood cell (RBC) transfusions
• Anemia without previous erythropoiesis-stimulating agent use (ESA-naïve) in adults with very low to intermediate risk myelodysplastic syndromes (MBS) who may require regular RBC transfusions
• Anemia failing an erythropoiesis-stimulating agent and requiring 2 or more RBC units over 8 weeks in adult patients with very low- to intermediate-risk myelodysplastic syndromes with ring sideroblasts (MDS-RS) or with myelodysplastic/myeloproliferative neoplasm with ring sideroblasts and thrombocytosis (MDS/MPN-RS-T).

Limitations of Use: Reblozyl is not indicated for use as a substitute for RBC transfusions in patients who require immediate correction of anemia.

It is not known if Reblozyl is safe and effective in children. 

Side effects

The most common side effects of Reblozyl are:

• stomach pain, diarrhea, or nausea
• headache, or dizziness
• feeling tired
• cough or trouble breathing
• muscle pain, bone pain, joint pain
• allergic reactions.

Serious side effects and warnings

Reblozyl may cause the following serious side effects:

• Blood clots. Blood clots in the arteries, veins, brain, and lungs have happened in people with beta-thalassemia during treatment with Reblozyl. The risk of blood clots may be higher in people who have had their spleen removed or who take hormone replacement therapy or birth control (oral contraceptives). Call your healthcare provider or get medical help right away if you get any of these symptoms:
  • chest pain
  • trouble breathing or shortness of breath
  • pain in your leg, with or without swelling
  • a cold or pale arm or leg
  • sudden numbness or weakness that are both short-term or continue to happen over a long period,
    especially on one side of the body
  • severe headache or confusion
  • sudden problems with vision, speech, or balance (such as trouble speaking, difficulty walking, or dizziness).
• High blood pressure.   Reblozyl may cause an increase in your blood pressure. Your healthcare provider will check your blood pressure before you receive your dose. Your healthcare provider may prescribe you medicine to treat high blood pressure or increase the dose of medicine you already take to treat high blood pressure if you develop high blood pressure during treatment with Reblozyl
• Extramedullary Hematopoietic (EMH) Masses. EMH masses have happened in people with beta-thalassemia during treatment with Reblozyl. You may have a higher risk of developing EMH masses if you have a history of EMH masses, have had your spleen removed, have or have had an enlarged spleen or liver, or have low hemoglobin levels. Your healthcare provider will monitor you before you start and during treatment with Reblozyl. Call your healthcare provider or get medical help right away if you get any of these symptoms:
  • severe back pain
  • numbness, weakness, or loss of voluntary movement in feet, legs, hands, or arms
  • loss of bowel and bladder control. 

Get emergency medical help if you have signs of an allergic reaction to Reblozyl, such as hives, difficulty breathing, or swelling of your face, lips, tongue, or throat.

Reblozyl may harm an unborn baby or cause fertility problems in females, which may affect your ability to become pregnant. Talk to your healthcare provider if this is a concern for you. See below for more information about pregnancy and breastfeeding.

This is not a complete list of side effects, and others may occur. Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

Related/similar drugs

Before receiving

Before receiving Reblozyl, tell your healthcare provider about all of your medical conditions, including if you:

• have or have had blood clots
• take hormone replacement therapy or birth control pills (oral contraceptives)
• have had your spleen removed (splenectomy)
• smoke
• have or have had high blood pressure (hypertension)
• have a history of extramedullary hematopoietic (EMH) masses
• have or have had an enlarged spleen or liver
• are pregnant or plan to become pregnant
• are breastfeeding or plan to breastfeed.

Pregnancy

Reblozyl may harm your unborn baby. Tell your healthcare provider right away if you become pregnant or think you may be pregnant during treatment with this medicine. If you are a female who can become pregnant:

• Your healthcare provider should do a pregnancy test before you start treatment
• You should use effective birth control (contraception) during treatment with Reblozyl and for at least 3 months after the last dose. 

Reblozyl may also cause fertility problems in females. This could affect your ability to become pregnant. Talk to your healthcare provider if this is a concern for you.

Breastfeeding

It is not known if this medicine passes into your breast milk. Do not breastfeed during treatment with Reblozyl and for 3 months after the last dose. Talk to your healthcare provider about the best way to feed your baby during this time.

How is Reblozyl administered?

Reblozyl is given by a healthcare provider as an injection under the skin (subcutaneously [SC]).

• Reblozyl is usually given 1 time every 3 weeks.
• Reblozyl injection may be administered under the skin of the upper arm, thigh, or stomach (abdomen).

Before each injection, you will need a blood test to check your hemoglobin levels to monitor if your anemia is getting better before each injection and during your treatment with Reblozyl.

• Be sure to tell your healthcare provider when you last had a blood transfusion.

Your blood pressure will need to be checked often.

• You may be given other medications to help control your blood pressure. Keep using this medicine for as long as your doctor has prescribed.

Dosing information

Usual Dose of Reblozyl for Beta-Thalassemia:

• Initial starting dose: Reblozyl 1 mg/kg SC once every 3 weeks.
  • If there is no reduction in RBC transfusion burden after 2 doses (6 weeks), increase to 1.25 mg/kg SC once every 3 weeks.
  • If there is no reduction in RBC transfusion burden after 3 consecutive doses (9 weeks) at 1.25 mg/kg SC once every 3 weeks, then treatment should be discontinued.
• Maximum dose: 1.25 mg/kg SC once every 3 weeks.

Your healthcare provider will measure your hemoglobin levels prior to treatment and modify your dosage as needed. See the Reblozyl Prescribing information for more detailed information about Reblozyl dosing, including dose modification according to hemoglobin levels.

Usual Dose of Reblozyl for Myelodysplastic Syndromes (MDS)

• Initial starting dose: Reblozyl 1 mg/kg SC once every 3 weeks.
  • If there is no reduction in RBC transfusion burden after 2 doses (6 weeks), increase to 1.33 mg/kg SC once every 3 weeks.
  • If there is no reduction in RBC transfusion burden after 2 consecutive doses (6 weeks) at 1.33 mg/kg SC once every 3 weeks, then increase the dose to 1.75 mg/kg every 3 weeks.
  • If there is no reduction in RBC transfusion burden, including no increase from baseline hemoglobin after at least 3 consecutive doses (9 weeks) at 1.75 mg/kg, then treatment should be discontinued.
• Maximum dose: 1.75 mg/kg.

Your healthcare provider will measure your hemoglobin levels prior to treatment and modify your dosage as needed. See the Reblozyl Prescribing information for more detailed information about Reblozyl dosing, including dose modification according to hemoglobin levels.

What happens if I miss a dose?

If you miss your Reblozyl injection, call your healthcare provider right away to reschedule your appointment. You should receive an injection as soon as you can, and then go back to your regular schedule. At least 3 weeks should pass between each injection.

Package Insert 

Review the Reblozyl Package Insert for more detailed information about this medicine. Discuss any medical questions you have with your doctor or other health care provider. This is not all the information you need to know about this medicine for safe and effective use, and it does not take the place of talking to your doctor about your treatment.

What other drugs will affect this medicine?

Other drugs may affect Reblozyl, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell your doctor about all your current medicines and any medicine you start or stop using.

Not all possible drug interactions are listed here. To check for interactions, click on the link below.

Ingredients

Active ingredient: luspatercept-aamt

Inactive ingredients: citric acid monohydrate, polysorbate 80, sucrose, and tri-sodium citrate dihydrate.

Reblozyl is available as:

• 25 mg lyophilized powder in a single-dose vial for reconstitution
• 75 mg lyophilized powder in a single-dose vial for reconstitution.

J Code is J0896.

Manufacturer

Reblozyl (luspatercept-aamt) is manufactured and marketed through a collaboration between Bristol Myers Squibb (BMS) and Merck (formerly known as Acceleron Pharma before Merck acquired it in 2021). Bristol Myers Squibb's global headquarters are in New York City, New York, USA. Merck's headquarters are in Kenilworth, New Jersey, USA.

Reblozyl Biosimilars

Biosimilar and interchangeable products are biological products that are highly similar to and have no clinically meaningful differences from the reference product.

Reference products

These are biological products that have already been approved by the FDA, against which biosimilar products are compared. There is 1 for Reblozyl.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Medical Disclaimer