Pasatru FDA Approval: A New Treatment Option for Adults Living With FOP
The U.S. Food and Drug Administration has approved Pasatru (garetosmab-grts) for adults living with fibrodysplasia ossificans progressiva, commonly known as FOP. The approval, announced by Regeneron Pharmaceuticals on August 19, 2026, marks an important development for people affected by this extremely rare genetic disorder, which causes abnormal bone to form in muscles, tendons, ligaments and other connective tissues.
FOP is a progressive condition that can severely restrict movement and interfere with everyday activities. Over time, abnormal bone formation, known as heterotopic ossification, can affect areas such as the jaw, spine, hips and rib cage. As these structures become affected, activities including walking, eating, speaking and breathing may become increasingly difficult.
Pasatru is designed to address one of the biological mechanisms involved in this abnormal bone formation. The treatment is a fully human monoclonal antibody that targets Activin A, a protein that has been linked to the development of heterotopic ossification in people with FOP.
What Is FOP?
Fibrodysplasia ossificans progressiva is an ultra-rare inherited disorder. It is caused by changes in the ACVR1 gene, which provides instructions for a receptor involved in bone and muscle biology.
In people with FOP, the body's normal processes for repairing tissues can result in abnormal bone formation. Instead of remaining as soft connective tissue, areas affected by the disease can gradually develop bone.
This process can occur following flare-ups, which may be triggered by injuries or other events. Because additional bone can restrict movement, repeated episodes can contribute to progressive disability.
According to information included in the announcement of Pasatru's approval, approximately 900 people worldwide are diagnosed with FOP. Many people with the condition experience substantial loss of mobility during adulthood.
The rarity of FOP has also made research challenging. Clinical studies often involve relatively small numbers of participants because so few people worldwide live with the disease. This makes the results of dedicated clinical trials particularly important when evaluating potential treatments.
How Does Pasatru Work?
Pasatru, also known as garetosmab-grts, is designed to block Activin A.
Researchers at Regeneron identified Activin A as an important factor in the biological process that contributes to heterotopic ossification in FOP. Pasatru is intended to bind to and neutralize Activin A, with the goal of reducing the development of new abnormal bone.
The treatment is administered intravenously. According to the information provided by Regeneron, the recommended starting dose is 10 mg per kilogram, given over approximately 60 minutes once every four weeks. If the starting dose is not tolerated, the dose may be reduced to 3 mg per kilogram, also administered once monthly.
Depending on the circumstances, treatment may be administered in different healthcare settings, including home infusion when appropriate.
What Did the Clinical Trial Show?
The FDA approval was supported by findings from the Phase 3 OPTIMA clinical trial.
The study included 63 adults with FOP. Participants were randomly assigned to receive Pasatru at either 10 mg/kg, Pasatru at 3 mg/kg, or placebo. Treatments were administered intravenously every four weeks for 56 weeks.
Researchers assessed the development of new heterotopic ossification lesions using whole-body CT scans. They also evaluated flare-ups, joint function and other measures of disease activity.
After 56 weeks, the study reported substantial reductions in new heterotopic ossification lesions among participants receiving Pasatru.
In the 10 mg/kg group, participants experienced two new lesions compared with 19 in the placebo group. This represented a reported 90% reduction.
The 3 mg/kg group experienced one new lesion compared with 19 in the placebo group, representing a reported 94% reduction.
The trial also examined clinician-assessed flare-ups. The 10 mg/kg group recorded nine flare-ups compared with 66 in the placebo group, an 88% reduction. The 3 mg/kg group recorded 53 flare-ups, representing a 15% reduction compared with placebo.
However, not every measure showed a statistically significant difference. The company reported that changes in patient-reported flare-ups through week 56 were not significantly different between the Pasatru and placebo groups.
These results illustrate why clinical trial findings need to be considered across multiple endpoints rather than relying on one result alone.
Safety Information
As with other prescription medicines, Pasatru carries important safety considerations.
The safety information provided with the approval warns that Pasatru can cause serious side effects. One major concern involves pregnancy. Pasatru should not be used during pregnancy because of the potential for harm to an unborn baby, including serious birth defects.
People who can become pregnant are advised to have a pregnancy test before starting treatment and to use effective contraception during treatment and for six months after the final dose. Anyone who becomes pregnant while receiving Pasatru should contact their healthcare provider immediately.
Skin and tissue infections are another important safety concern. These may include abscesses and bacterial infections such as cellulitis. People receiving treatment should seek medical attention if they develop symptoms such as redness, warmth, swelling, pain, tenderness, fever or a general feeling of illness.
Nosebleeds can also occur. Medical attention may be necessary if a nosebleed is severe, does not stop with basic first-aid measures, or continues for more than 20 minutes.
Reported common side effects include abscesses, acne, increased hair growth, loss of eyebrows or eyelashes, mouth sores, nosebleeds, folliculitis, nail infections and rash.
The available safety information also advises patients to tell their healthcare provider about other medicines, vitamins and herbal supplements they are taking. Breastfeeding is not recommended during treatment and for six months after the final dose, according to the provided prescribing information.
What Could the Approval Mean for People With FOP?
The FDA approval provides adults with FOP with another treatment option specifically aimed at reducing new abnormal bone formation and clinician-assessed flare-ups.
For a disease as rare and disabling as FOP, treatment development can take many years. The approval also reflects decades of scientific research into the biological mechanisms behind the disease.
It is important to understand that reducing new lesions does not necessarily mean reversing bone that has already formed. FOP remains a complex, progressive condition, and treatment decisions need to be individualized by qualified healthcare professionals.
Regeneron has also announced plans for additional research involving younger patients. A Phase 3 study called OPTIMA 2 is planned for children and adolescents with FOP. The results of future studies will help researchers understand how Pasatru may perform in different age groups.
What Happens Next?
Pasatru's approval currently applies to adults with FOP in the United States. Regulatory review is also underway in the European Union, according to Regeneron, with additional submissions planned in other countries.
The availability of the treatment, insurance coverage, infusion arrangements and eligibility requirements may vary. Patients and families should discuss these practical considerations with their healthcare team.
Regeneron has also established its myRARE program to provide resources related to product information, insurance benefit verification and potential financial assistance.
For people living with FOP, the FDA approval of Pasatru represents a new chapter in treatment research. The therapy does not eliminate the underlying genetic condition, but its ability to reduce new heterotopic ossification lesions in the OPTIMA trial provides evidence for a targeted approach to managing an important part of the disease.
As research continues, future studies may provide additional information about long-term treatment, younger patients, safety and the potential impact on disease progression. For now, patients considering Pasatru should review the potential benefits and risks with their healthcare professional and use the medicine only as prescribed.
Sources
- Regeneron Pharmaceuticals, Inc., announcement regarding the FDA approval of Pasatru (garetosmab-grts) for adults with fibrodysplasia ossificans progressiva, August 19, 2026.
- Information on the OPTIMA Phase 3 clinical trial and Pasatru safety information as reproduced in the supplied source material.
- U.S. Food and Drug Administration, prescribing and regulatory information for approved medicines.
Medical Disclaimer
This article is provided for general educational and informational purposes only. It is not intended to provide medical advice, diagnosis or treatment, and it should not be used as a substitute for consultation with a qualified healthcare professional. Pasatru is a prescription medicine and has important risks and safety considerations. Patients should discuss their individual medical history, medications, pregnancy or breastfeeding status, and treatment options with their healthcare provider. Do not start, stop or change a prescription medicine without appropriate medical guidance.