What happened
On August 19, 2026, the FDA approved Pasatru (garetosmab-grts) to reduce new heterotopic ossification and reduce clinician-assessed disease flare-ups in adults with fibrodysplasia ossificans progressiva, or FOP. The agency said Pasatru is the second drug approved for patients with the disease and granted the approval to Regeneron Pharmaceuticals, Inc. The recommended starting dose is 10 mg/kg by intravenous infusion over 60 minutes once every four weeks, with a reduction to 3 mg/kg every four weeks if 10 mg/kg is not tolerated.
FDA said approval was supported by a randomized, double-blind, placebo-controlled study in 63 adults with FOP, with treatment given every four weeks for 56 weeks. By Week 56, both Pasatru dose groups significantly reduced new bone growth versus placebo. There were 2 new lesions among 23 patients at 10 mg/kg and 1 new lesion among 19 patients at 3 mg/kg, compared with 19 new lesions among 21 patients on placebo. Clinician-assessed flare-ups over 56 weeks were 9 with 10 mg/kg, 53 with 3 mg/kg, and 66 with placebo. Pasatru previously received Breakthrough Therapy, Fast Track, Orphan Drug, and Priority Review designations for this indication.
Why it matters
The immediate read is that FDA has now validated a second regulatory path in FOP, but with a very specific clinical claim set: reducing new heterotopic ossification and reducing clinician-assessed flare-ups in adults. For payers and investors, the filing provides unusually concrete trial outputs in a very small population. The separation between the two dose arms on flare-ups will likely shape real-world utilization discussions.
Both the 10 mg/kg arm and the 3 mg/kg arm reduced new lesion formation versus placebo. The flare-up counts, however, were much more favorable at 10 mg/kg, while the label also allows dose reduction if 10 mg/kg is not tolerated.
For Regeneron, this looks like an ultra-rare-disease approval with meaningful clinical specificity, but not a frictionless launch. Pasatru is an infused antibody dosed every four weeks, and the label carries a warning for fetal harm during pregnancy, plus warnings for skin and soft tissue infections requiring treatment or hospitalization and for nose bleeding requiring medical intervention.
The likely implication is that access discussions will center on adult FOP patients, site-of-care logistics, and how plans interpret the benefit-risk profile against the magnitude of lesion reduction seen versus placebo. Analysts will also watch whether this second approval changes the competitive tone in FOP more broadly. For clinical reference on rare-disease therapies, see ClinicalRx.ai. For payer-side drug pricing context, see RxInfo.ai.
