Pasatru (garetosmab-grts)
An approved treatment for Fibrodysplasia Ossificans Progressiva.
The same compound appears under different names depending on the context. Here is how to identify Garetosmab-grts wherever you encounter it, plus the key facts at a glance.
- Generic name
- Garetosmab-grts
- Brand name
- Pasatru
- Development code
- REGN2477
- Drug class
- Activin A-blocking monoclonal antibody (activin signaling inhibitor)
- Manufacturer
- Regeneron Pharmaceuticals
- How it's taken
- The starting dose is 10 mg per kg of body weight, given as an IV infusion over 60 minutes once every 4 weeks using an infusion pump.
An IV infusion given once every 4 weeks, approved by the FDA on August 19, 2026 to reduce new abnormal bone growth (heterotopic ossification) and clinician-assessed flare-ups in adults with fibrodysplasia ossificans progressiva. In its main trial, new bone lesions at 56 weeks were 90% lower on the starting dose than on placebo. It was the second FOP drug approved, after Sohonos in 2023.
Where Garetosmab-grts fits
The second of 3 FOP medicines approved by the FDA, and the only one given as an antibody infusion. Sohonos (palovarotene) capsules were approved in August 2023 and Atebrioz (zilurgisertib) in September 2026; no trial has compared them with each other.
How Garetosmab-grts works
In FOP, a change in the ACVR1 gene, which makes a receptor also called ALK2, lets the receptor be switched on by activin A. When activin A activates the altered receptor, muscles, tendons and ligaments can turn into bone, often after painful flare-ups. Pasatru is a human antibody that attaches to activin A and blocks its signal, which reduces the formation of new bone lesions. It is approved to reduce new bone lesions and flare-ups; the label does not claim that it removes bone that has already formed.
Mechanism: Fully human monoclonal antibody that binds and blocks activin A, the signal that switches on the mutant ACVR1 (ALK2) receptor and drives new bone formation in FOP
Side effects and safety
- Harm to an unborn baby. Must not be used in pregnancy. Pregnancy test before starting, effective birth control during treatment and for 6 months after the last dose, and stop right away if pregnancy occurs.
- Skin and soft tissue infections. Abscesses and cellulitis, some needing treatment or hospitalization, have occurred. Report redness, pain, swelling or fever.
- Nosebleeds. Spontaneous nosebleeds, including serious ones, have been reported. Get medical care for a nosebleed that is severe, lasts more than 20 minutes or does not stop with first aid.
- Breastfeeding and male fertility. Breastfeeding is not recommended during treatment and for 6 months after. Animal studies suggest it may impair male fertility.
- Pregnancy test before starting in women who could become pregnant
- Report signs of skin infection such as redness, warmth, swelling, pain or fever
- Get medical care for severe or long-lasting nosebleeds
Pasatru has no boxed warning, but it must not be used during pregnancy because it can harm an unborn baby. A pregnancy test is needed before starting, and women who could become pregnant should use effective birth control during treatment and for 6 months after the last dose. The label also warns about skin and soft tissue infections, such as abscesses (pus-filled lumps) and cellulitis, some needing treatment or a hospital stay, and about nosebleeds, including 1 serious case that needed hospital care. In the main trial, side effects on the 10 mg/kg dose, the 3 mg/kg dose and placebo included abscess (35%, 11% and 10%), acne (30%, 16% and 10%), increased hair growth (26%, 42% and 0%), loss of eyebrow or eyelash hair, called madarosis (26%, 16% and 19%), mouth sores (26%, 5% and 5%) and nosebleeds (17%, 53% and 24%). Breastfeeding is not recommended during treatment and for 6 months after, and animal studies suggest it may affect male fertility[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 Garetosmab-grts
The starting dose is 10 mg per kg of body weight, given as an IV infusion over 60 minutes once every 4 weeks using an infusion pump. If 10 mg/kg is not tolerated, the dose can be lowered to 3 mg/kg every 4 weeks. A missed dose should be given as soon as possible, with the schedule restarting every 4 weeks from that date. Women who could become pregnant need a pregnancy test before the first dose[1]. Regeneron says it can be given in a range of care settings, including home infusion where appropriate[4].
Availability and cost
Only available as the brand-name product.
Help paying for Pasatru
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.
- Insurance and case manager help
Product information, insurance benefit verification and information about potential financial support for Pasatru.
The official page does not say who qualifies. Ask the program. · source
Good to know: myRARE.com and pasatru.com blocked automated access, so the program was confirmed from Regeneron's August 19, 2026 approval press release and search listings of myRARE.com, which mention Patient Support Managers who check eligibility for myRARE financial support programs. No Pasatru copay or free-drug terms were verified. Phone is 1-833-4my-RARE.
- From a charity · International FOP AssociationDental Care Travel Stipend Program fundApply directly
Pays for: Travel and lodging to see an FOP dental expert for medically necessary procedures, up to $1,500 per year.
The foundation says: “Status not shown on page”
Access and eligibility
Approved for adults with FOP. Safety and effectiveness in children have not been established, and it must not be used during pregnancy. The OPTIMA trial enrolled adults 18 and older with a confirmed FOP-causing ACVR1 change, signs of active disease and a joint involvement (CAJIS) score of 19 or less out of 30.
Source: Regeneron myRARE
Access program details are provided for informational purposes and may vary based on insurance coverage, geographic location, and individual circumstances. Confirm current eligibility directly with the manufacturer or your specialty pharmacy.
Clinical trial results
Approval rested on OPTIMA (NCT05394116), a Phase 3 trial in 63 adults with FOP (median age 25, range 18 to 42) randomly assigned to Pasatru 10 mg/kg, Pasatru 3 mg/kg or placebo every 4 weeks for 56 weeks. On low-dose whole-body CT scans, 5 of 21 placebo patients developed a total of 19 new bone lesions, against 2 lesions in 2 of 23 patients on 10 mg/kg and 1 lesion in 1 of 19 on 3 mg/kg, reductions of 90% and 94%. Clinician-assessed flare-ups totaled 9 on 10 mg/kg, 53 on 3 mg/kg and 66 on placebo; the 10 mg/kg dose clearly reduced flare-ups (rate ratio 0.12), the 3 mg/kg dose did not, and patient-reported flare-ups did not differ significantly between groups. The volume of new bone was lower on both doses, but that difference was not statistically significant[1][6]. Regeneron reported the 10 mg/kg flare-up reduction as 88%[4], and the trial was published in The Lancet on September 28, 2026[5].
Development history
Regeneron scientists discovered that activin A drives abnormal bone formation in FOP, and the company developed garetosmab under the code REGN2477[4][6]. It received Breakthrough Therapy, Fast Track, Orphan Drug and Priority Review designations, and the FDA approved it on August 19, 2026 as the second drug for FOP[3][2], after Sohonos (palovarotene) on August 16, 2023[7]. At approval, Regeneron said a Phase 3 trial in children and teenagers, OPTIMA 2, was planned to begin later in 2026 and a European application was under review[4]. Atebrioz (zilurgisertib) became the third FDA-approved FOP drug on September 25, 2026[8].
Explore Fibrodysplasia Ossificans Progressiva trials
Other Fibrodysplasia Ossificans Progressiva treatments
FOP has 3 FDA-approved medicines: Sohonos (palovarotene) capsules since August 16, 2023 for adults and for girls 8 and older and boys 10 and older, Pasatru (garetosmab) infusions since August 19, 2026 for adults, and Atebrioz (zilurgisertib) since September 25, 2026 for people 12 and older. All 3 aim to reduce new heterotopic bone, and no head-to-head trial has compared them.
Common questions about Garetosmab-grts
▸What is Garetosmab-grts (Pasatru)?
An IV infusion given once every 4 weeks, approved by the FDA on August 19, 2026 to reduce new abnormal bone growth (heterotopic ossification) and clinician-assessed flare-ups in adults with fibrodysplasia ossificans progressiva. In its main trial, new bone lesions at 56 weeks were 90% lower on the starting dose than on placebo. It was the second FOP drug approved, after Sohonos in 2023.
▸How does Garetosmab-grts work?
In FOP, a change in the ACVR1 gene, which makes a receptor also called ALK2, lets the receptor be switched on by activin A. When activin A activates the altered receptor, muscles, tendons and ligaments can turn into bone, often after painful flare-ups. Pasatru is a human antibody that attaches to activin A and blocks its signal, which reduces the formation of new bone lesions. It is approved to reduce new bone lesions and flare-ups; the label does not claim that it removes bone that has already formed.
▸What are the side effects of Garetosmab-grts?
Pasatru has no boxed warning, but it must not be used during pregnancy because it can harm an unborn baby. A pregnancy test is needed before starting, and women who could become pregnant should use effective birth control during treatment and for 6 months after the last dose. The label also warns about skin and soft tissue infections, such as abscesses (pus-filled lumps) and cellulitis, some needing treatment or a hospital stay, and about nosebleeds, including 1 serious case that needed hospital care. In the main trial, side effects on the 10 mg/kg dose, the 3 mg/kg dose and placebo included abscess (35%, 11% and 10%), acne (30%, 16% and 10%), increased hair growth (26%, 42% and 0%), loss of eyebrow or eyelash hair, called madarosis (26%, 16% and 19%), mouth sores (26%, 5% and 5%) and nosebleeds (17%, 53% and 24%). Breastfeeding is not recommended during treatment and for 6 months after, and animal studies suggest it may affect male fertility[1].
▸How is Garetosmab-grts taken?
The starting dose is 10 mg per kg of body weight, given as an IV infusion over 60 minutes once every 4 weeks using an infusion pump. If 10 mg/kg is not tolerated, the dose can be lowered to 3 mg/kg every 4 weeks. A missed dose should be given as soon as possible, with the schedule restarting every 4 weeks from that date. Women who could become pregnant need a pregnancy test before the first dose[1]. Regeneron says it can be given in a range of care settings, including home infusion where appropriate[4].
▸Is Garetosmab-grts FDA approved?
Yes, Garetosmab-grts (Pasatru) is FDA approved (2026) for the treatment of Fibrodysplasia Ossificans Progressiva.
▸Is Pasatru approved for children with FOP?
No. Pasatru is approved only for adults, and its label says safety and effectiveness in children have not been established. At approval, Regeneron said a Phase 3 trial in children and teenagers, called OPTIMA 2, was planned to begin later in 2026. For younger patients, Sohonos is approved from age 8 in girls and age 10 in boys, and Atebrioz from age 12.
▸How is Pasatru given?
As an IV infusion over 60 minutes once every 4 weeks, starting at 10 mg per kg of body weight. The dose can be lowered to 3 mg/kg if the higher dose is not tolerated. Regeneron says it can be given in different care settings, including home infusion where appropriate, which may matter for people with limited mobility.
▸What are the side effects of Pasatru?
In the OPTIMA trial, common side effects on the 10 mg/kg dose included abscesses (35% against 10% on placebo), acne (30% against 10%), increased hair growth (26%), loss of eyebrow or eyelash hair (26%), mouth sores (26%) and nosebleeds. It must not be used in pregnancy, and the label warns about skin infections and serious nosebleeds.
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. PASATRU (garetosmab-grts) injection, for intravenous use: prescribing information. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=0d5cec96-b02b-4f1d-bc66-51e62ce04e3c
- U.S. Food and Drug Administration · 2026-08-19. BLA 761508 approval letter. https://www.accessdata.fda.gov/drugsatfda_docs/appletter/2026/761508Orig1s000ltr.pdf
- U.S. Food and Drug Administration · 2026-08-19. FDA Approves Second Treatment for Fibrodysplasia Ossificans Progressiva. https://www.fda.gov/drugs/news-events-human-drugs/fda-approves-second-treatment-fibrodysplasia-ossificans-progressiva
- Regeneron Pharmaceuticals · 2026-08-19. Pasatru (garetosmab-grts) First and Only FDA-approved Treatment Demonstrating Reduction in New Heterotopic Ossification (HO) Lesions and Clinician-Assessed Flare-ups in a Placebo-controlled Trial in Adults with Fibrodysplasia Ossificans Progressiva (FOP). https://investor.regeneron.com/news-releases/news-release-details/pasatrutm-garetosmab-grts-first-and-only-fda-approved-treatment
- The Lancet · 2026-09-28. Efficacy and safety of garetosmab, an activin A-blocking antibody, in fibrodysplasia ossificans progressiva (OPTIMA): a randomised, double-blind, placebo-controlled, phase 3 trial. https://pubmed.ncbi.nlm.nih.gov/42805227/
- ClinicalTrials.gov. A Study to Assess Safety, Tolerability and Efficacy of Garetosmab Versus Placebo Administered Intravenously (IV) in Adult Participants With Fibrodysplasia Ossificans Progressiva (FOP) (OPTIMA). https://clinicaltrials.gov/study/NCT05394116
- U.S. Food and Drug Administration · 2023-08-16. NDA 215559 approval letter. https://www.accessdata.fda.gov/drugsatfda_docs/appletter/2023/215559Orig1s000ltr.pdf
- U.S. Food and Drug Administration. Novel Drug Approvals for 2026. https://www.fda.gov/drugs/novel-drug-approvals-fda/novel-drug-approvals-2026