Rytelo (imetelstat)
An approved treatment for Myelodysplastic Syndromes.
The same compound appears under different names depending on the context. Here is how to identify Imetelstat wherever you encounter it, plus the key facts at a glance.
- Generic name
- Imetelstat
- Brand name
- Rytelo
- Development code
- GRN163L
- Drug class
- Telomerase inhibitor (oligonucleotide)
- Manufacturer
- Geron Corporation
- How it's taken
- The dose is 7.
An IV infusion given every 4 weeks, approved by the FDA on June 6, 2024 for adults with lower-risk myelodysplastic syndromes (low or intermediate-1 risk) who need 4 or more red blood cell units every 8 weeks and whose anemia has not responded to, has stopped responding to, or is not suited to erythropoiesis-stimulating agents (ESAs, drugs such as epoetin). In its main trial, 40% of patients went at least 8 weeks without a transfusion, against 15% on placebo.
Where Imetelstat fits
A treatment for transfusion-dependent anemia in lower-risk MDS after ESAs have failed or cannot be used. It works by blocking telomerase, a different approach from luspatercept (Reblozyl), an erythroid maturation agent also approved for anemia in lower-risk MDS.
How Imetelstat works
Telomerase is an enzyme that rebuilds telomeres, the protective caps on the ends of chromosomes, which lets cells keep dividing. Telomerase activity is increased in MDS and in malignant stem and progenitor cells. Imetelstat is a short, modified strand of genetic material (an oligonucleotide) that binds the RNA template inside telomerase and blocks the enzyme. In lab studies this shortened telomeres, slowed the growth of the malignant stem and progenitor cells and caused them to die[1].
Mechanism: Oligonucleotide telomerase inhibitor that binds the RNA template of human telomerase, blocking the enzyme that abnormal MDS stem and progenitor cells rely on
Side effects and safety
- Low platelets (thrombocytopenia). Severe drops in 65% of patients. Blood counts are checked often, and platelet transfusions may be given. Report unusual bleeding or bruising.
- Low neutrophils (neutropenia). Severe drops in 72% of patients, with sepsis in 4.2%. Report fever or signs of infection right away.
- Infusion-related reactions. In 8% of patients, including a hypertensive crisis in 0.8%. Premedication before every infusion and monitoring for at least 1 hour after.
- Harm to an unborn baby. Pregnancy test before starting, and effective contraception during treatment and for 1 week after the last dose.
- Complete blood counts before starting, weekly for the first 2 cycles, then before each cycle
- Liver tests before starting, weekly for the first cycle, then before each cycle
- Premedication with diphenhydramine and hydrocortisone before each infusion and observation for at least 1 hour after
- Pregnancy test before starting in women who could become pregnant
Rytelo has no boxed warning and no contraindications. Its main risk is low blood counts. In the IMerge trial, severe (grade 3 or 4) drops in platelets occurred in 65% of patients vs 8% on placebo, and severe drops in neutrophils, the white blood cells that fight bacteria, in 72% vs 7%. The median time to a first severe drop was 6 weeks for platelets and 4.6 weeks for neutrophils, and the median recovery from each episode took under 2 weeks. Grade 3 or 4 bleeding occurred in 2.5% of patients and sepsis in 4.2%. Other side effects more common than on placebo included fatigue (29% vs 20%), joint and muscle pain (25% vs 19%), COVID-19 (19% vs 14%), headache (13% vs 5%) and infusion-related reactions (8% vs 3.4%). Dose delays for side effects were needed in 80% of patients and dose reductions in 49%. Based on animal studies, it can harm an unborn baby[1].
This is not a complete list of side effects. Talk to your doctor or pharmacist about what to expect and when to seek medical attention.
Taking Imetelstat
The dose is 7.1 mg/kg given by a healthcare provider as an IV infusion over 2 hours every 4 weeks. At least 30 minutes before each infusion, patients receive diphenhydramine (25 to 50 mg) and hydrocortisone (100 to 200 mg) to prevent infusion reactions, and they are watched for at least 1 hour afterward. For low blood counts or other side effects, doses can be delayed or lowered to 5.6 mg/kg and then 4.4 mg/kg. Treatment should stop if transfusion needs have not dropped after 24 weeks (6 doses)[1].
Availability and cost
Only available as the brand-name product.
Help paying for Rytelo
Pick your insurance to see which help fits. Drugmaker copay cards can't be used with Medicare, Medicaid or TRICARE; charity funds are the usual route there.
- Copay help
REACH4RYTELO Copay Program: eligible commercially insured patients may pay as little as $0, with up to $9,450 a year toward Rytelo plus $100 per infusion (up to $1,200 a year) toward administration costs. Residents of MA, MI, MN and RI get drug help only. No income information required; resets January 1. Not for Medicaid, Medicare, TRICARE, VA or other government insurance.
For: private insurance · source - Free medicine program
Geron's REACH4RYTELO enrollment form lists a Patient Assistance Program that may provide free medication and asks for household income. Eligibility limits are not published.
The official page does not say who qualifies. Ask the program. · source - Bridge or quick-start supply
A Bridge Program is listed on the REACH4RYTELO enrollment form. Terms are not published.
The official page does not say who qualifies. Ask the program. · source
Good to know: Phone is 1-844-4RYTELO. The doctors' page and enrollment form give hours of Monday to Friday, 8 AM to 5 PM ET. Copay terms are also in the August 2026 brochure: https://www.rytelo.com/wp-content/uploads/RYTELO_Patient_Copay_Program_Brochure.pdf.
- From a charity · Blood Cancer United (formerly The Leukemia & Lymphoma Society)Clinical Trials Co-Pay Fund (all blood cancers) fundOpen
Pays for: Insurance premiums and treatment-related copays, deductibles and coinsurance, up to $3,500 per year. Requires health insurance (any kind).
- From a charity · Blood Cancer United (formerly The Leukemia & Lymphoma Society)Patient Aid Program fundOpen
Pays for: One-time $100 stipend for non-medical expenses (transportation, food, housing, utilities); no income or insurance requirement, up to $100 per year.
The foundation says: “CURRENT FUND STATUS: Open. Fund is currently Open.” - From a charity · HealthWell FoundationMyelodysplastic Syndromes (Medicare Access) fundOpen
Pays for: Copays, premiums or other treatment costs. Medicare patients only.
Clinical trial results
IMerge (NCT02598661) randomized 178 adults with lower-risk MDS who needed at least 4 red cell units over 8 weeks and whose disease had not responded to, had stopped responding to, or was not suited to ESAs, to Rytelo or placebo (2:1). People with the del(5q) abnormality or prior lenalidomide or hypomethylating agent treatment were excluded. At least 8 weeks without any transfusion was reached by 39.8% on Rytelo vs 15.0% on placebo, and at least 24 weeks by 28.0% vs 3.3%. About 62% of patients had ring sideroblasts, an MDS subtype[1][5]. The Phase 3 results were published in The Lancet[6].
Development history
Explore Myelodysplastic Syndromes trials
Common questions about Imetelstat
▸What is Imetelstat (Rytelo)?
An IV infusion given every 4 weeks, approved by the FDA on June 6, 2024 for adults with lower-risk myelodysplastic syndromes (low or intermediate-1 risk) who need 4 or more red blood cell units every 8 weeks and whose anemia has not responded to, has stopped responding to, or is not suited to erythropoiesis-stimulating agents (ESAs, drugs such as epoetin). In its main trial, 40% of patients went at least 8 weeks without a transfusion, against 15% on placebo.
▸How does Imetelstat work?
Telomerase is an enzyme that rebuilds telomeres, the protective caps on the ends of chromosomes, which lets cells keep dividing. Telomerase activity is increased in MDS and in malignant stem and progenitor cells. Imetelstat is a short, modified strand of genetic material (an oligonucleotide) that binds the RNA template inside telomerase and blocks the enzyme. In lab studies this shortened telomeres, slowed the growth of the malignant stem and progenitor cells and caused them to die[1].
▸What are the side effects of Imetelstat?
Rytelo has no boxed warning and no contraindications. Its main risk is low blood counts. In the IMerge trial, severe (grade 3 or 4) drops in platelets occurred in 65% of patients vs 8% on placebo, and severe drops in neutrophils, the white blood cells that fight bacteria, in 72% vs 7%. The median time to a first severe drop was 6 weeks for platelets and 4.6 weeks for neutrophils, and the median recovery from each episode took under 2 weeks. Grade 3 or 4 bleeding occurred in 2.5% of patients and sepsis in 4.2%. Other side effects more common than on placebo included fatigue (29% vs 20%), joint and muscle pain (25% vs 19%), COVID-19 (19% vs 14%), headache (13% vs 5%) and infusion-related reactions (8% vs 3.4%). Dose delays for side effects were needed in 80% of patients and dose reductions in 49%. Based on animal studies, it can harm an unborn baby[1].
▸How is Imetelstat taken?
The dose is 7.1 mg/kg given by a healthcare provider as an IV infusion over 2 hours every 4 weeks. At least 30 minutes before each infusion, patients receive diphenhydramine (25 to 50 mg) and hydrocortisone (100 to 200 mg) to prevent infusion reactions, and they are watched for at least 1 hour afterward. For low blood counts or other side effects, doses can be delayed or lowered to 5.6 mg/kg and then 4.4 mg/kg. Treatment should stop if transfusion needs have not dropped after 24 weeks (6 doses)[1].
▸Is Imetelstat FDA approved?
Yes, Imetelstat (Rytelo) is FDA approved (2024) for the treatment of Myelodysplastic Syndromes.
▸Who can get Rytelo for MDS?
Adults with low or intermediate-1 risk MDS who need 4 or more red blood cell units over 8 weeks and whose anemia has not responded to, has stopped responding to, or is not suited to ESAs such as epoetin. The main trial did not include people with del(5q) MDS or people who had taken lenalidomide or a hypomethylating agent.
▸What are the side effects of Rytelo?
The main risks are low platelets and low neutrophils, which were severe in 65% and 72% of patients in the IMerge trial and usually recovered in under 2 weeks. Fatigue, joint and muscle pain, COVID-19, headache and infusion reactions were also more common than on placebo. Blood counts are checked weekly for the first 2 cycles and before each later dose.
▸How long does it take to know if Rytelo is working?
The label says to stop Rytelo if transfusion needs have not dropped after 24 weeks, which is 6 doses given every 4 weeks. In the IMerge trial, 39.8% of patients went at least 8 weeks without a transfusion and 28.0% went at least 24 weeks, compared with 15.0% and 3.3% on placebo.
Sources and references
Every factual claim on this page is drawn from the public sources listed below. Click any reference to open the original document.
- U.S. National Library of Medicine, DailyMed. RYTELO (imetelstat) for injection, for intravenous use: prescribing information. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=b0fab7ca-e578-43c5-9df6-bdaff4182257
- U.S. Food and Drug Administration · 2024-06-06. NDA 217779 approval letter. https://www.accessdata.fda.gov/drugsatfda_docs/appletter/2024/217779Orig1s000ltr.pdf
- Geron Corporation (SEC filing) · 2024-06-06. Geron announces FDA approval of RYTELO (imetelstat) (Form 8-K exhibit). https://www.sec.gov/Archives/edgar/data/886744/000095017024070574/gern-ex99_1.htm
- Geron Corporation (Business Wire) · 2025-03. Geron announces European Commission marketing authorization for RYTELO (imetelstat). https://www.businesswire.com/news/home/20250311485595/en/
- ClinicalTrials.gov. Study to Evaluate Imetelstat (GRN163L) in Participants With International Prognostic Scoring System (IPSS) Low or Intermediate-1 Risk Myelodysplastic Syndrome (MDS) (IMerge). https://clinicaltrials.gov/study/NCT02598661
- The Lancet. Imetelstat in patients with lower-risk myelodysplastic syndromes who have relapsed or are refractory to erythropoiesis-stimulating agents (IMerge): a multinational, randomised, double-blind, placebo-controlled, phase 3 trial. https://doi.org/10.1016/S0140-6736(23)01724-5
- U.S. National Library of Medicine, DailyMed. REBLOZYL (luspatercept-aamt) for injection: prescribing information. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=82f4d266-3f52-41eb-86ba-0abf3cf468e8
- Geron Corporation. RYTELO patient support. https://www.rytelo.com/patient-support/