Regeneron's Pasatru wins FDA nod as second FOP therapy, first to cut flare-ups and new bone lesions

The US Food and Drug Administration has cleared Regeneron's Pasatru (garetosmab) for adults with fibrodysplasia ossificans progressiva, marking the second approved treatment for this ultra-rare condition and the first to show meaningful reductions in both new heterotopic ossification lesions and clinician-assessed flare-ups.

What changed for FOP patients?

Fibrodysplasia ossificans progressiva is a rare genetic disease in which soft tissues such as muscle, tendon and ligament gradually turn into bone outside the skeleton, leading to stiff joints, loss of mobility and, in advanced cases, breathing and swallowing difficulties. Only around 900 people worldwide are known to have FOP, and many become dependent on a wheelchair by their thirties, with a median survival in the mid-fifties.

What is Pasatru and what is it's mechanism of action?

Pasatru is a fully human monoclonal antibody that neutralizes Activin A, a protein Regeneron identified as a key driver of abnormal bone formation in FOP. By blocking Activin A, the drug aims to slow or prevent the progressive immobilization that defines the disease.

OPTIMA trial: How Pasatru performed?

Approval rests on the Phase 3 OPTIMA study, a randomized, placebo-controlled trial in 63 adults with active FOP. Participants received either 10 mg/kg Pasatru, 3 mg/kg Pasatru, or placebo by intravenous infusion every four weeks for 56 weeks.

Key efficacy findings at week 56:

• New heterotopic ossification lesions fell by about 90 percent with the 10 mg/kg dose and 94 percent with the 3 mg/kg dose versus placebo, based on whole-body CT scans.

• Clinician-assessed flare-ups dropped sharply with the higher dose: nine events in the 10 mg/kg group compared with 66 on placebo, an 88 percent relative reduction.

• The lower 3 mg/kg dose showed 53 flare-ups, a smaller 15 percent reduction versus placebo, while patient-reported flare-up rates did not differ significantly across groups.

Safety signals were consistent with the small sample size and rare-disease setting. Serious treatment-emergent adverse events occurred in two patients on 10 mg/kg, one on 3 mg/kg, and two on placebo.

Dosing, access and care setting of Pasatru

Pasatru is supplied as a 300 mg/5 mL single-dose vial for intravenous use. The recommended starting regimen is 10 mg/kg infused over 60 minutes once every four weeks, with an option to reduce to 3 mg/kg if tolerability is a concern. Regeneron notes the therapy can be delivered in multiple care environments, including home infusion when clinically appropriate, which may ease access for patients with limited mobility.

For US patients, Regeneron's myRARE support program provides benefits verification, product information and potential financial assistance resources.

Regulatory path and what's next

• Pasatru is the second FDA-approved medicine for FOP after Ipsen's Sohonos in 2023, but it is the first to demonstrate reductions in both lesion formation and clinician-assessed flares in a controlled trial.

• The European Medicines Agency is reviewing a marketing application, and additional filings are planned in other regions including Japan. The drug previously received FDA Fast Track and Orphan Drug designations, along with orphan status in the EU and Japan.

A pediatric and adolescent Phase 3 study, OPTIMA 2, is expected to start later this year to evaluate Pasatru in younger patients.

Why this matters for the FOP community

For a condition with no cure and very limited treatment options, a therapy that can substantially slow new bone formation and reduce inflammatory flare-ups could translate into longer preservation of movement and function. Clinicians will now weigh Pasatru against existing options, considering route of administration, monitoring needs, and individual patient profiles.