Atebrioz (zilurgisertib): FDA approval, pivotal trial and safety
Approved
Type
New molecular entity · Oral
FDA-approved use
To reduce the volume of total new heterotopic ossification in adults and pediatric patients 12 years and older with fibrodysplasia ossificans progressivaWording from FDA's list of novel approvals.
FDA review
Priority reviewOrphan drug
Company
Mirum
Application
NDA 221198
Specialty
Genetics
At a glance
Atebrioz (zilurgisertib) is an oral ALK2 inhibitor approved to reduce the volume of new heterotopic ossification in adults and children 12 years and older with fibrodysplasia ossificans progressiva (FOP). In the pivotal placebo-controlled trial, total new heterotopic ossification volume at Week 24 fell slightly with treatment and rose with placebo, a Hodges-Lehmann difference of -15.8 cm3 (95% CI -32.1 to -6.0). The main safety point is embryo-fetal toxicity; there is no boxed warning.
What it is and how it works
FOP is caused by a gain-of-function mutation in the ACVR1 gene, which encodes the ALK2 receptor in the bone morphogenetic protein pathway. The overactive signaling drives heterotopic bone formation. Zilurgisertib selectively inhibits both wild-type ALK2 and the pathogenic R206H mutant form, which reduces endochondral bone formation. It is taken by mouth.
Randomized, double-blind, placebo-controlled trial with a 24-week blinded period, followed by a long open-label extension of treatment.
Patients
63 patients with FOP (28 adults and 35 aged 12 years and older). Median age was 16 years. All had a baseline CAJIS score of 23 or lower, and 84% had a score below 18. Patients had recent patient-reported disease activity.
Compared with
Placebo, randomized 1:1, stratified by baseline CAJIS score.
Primary endpoint
Total new heterotopic ossification lesion volume on whole-body CT (excluding the head) at Week 24 versus placebo. This includes growth of existing lesions and new discrete lesions.
Result
Mean change from baseline was -3.2 cm3 (SD 19.9) with zilurgisertib and +24.6 cm3 (SD 51.9) with placebo. The Hodges-Lehmann treatment difference was -15.8 cm3 (95% CI -32.1 to -6.0).
Other results
Not described in the sources provided.
Safety in the trial
Adverse reactions in 10% or more of treated patients and more often than with placebo: headache (22% vs 16%), arthralgia (22% vs 10%), upper respiratory tract infection (22% vs 10%), epistaxis (13% vs 0), and nausea (13% vs 3%). Gastroenteritis, reflux, iron deficiency anemia, and rash occurred in 3 patients each and alopecia in 2, all only with zilurgisertib. Mean serum iron, hemoglobin, and transferrin saturation rose but stayed in the normal range.
How does Atebrioz (zilurgisertib) compare with the alternatives (Palovarotene, Garetosmab, Glucocorticoids) for its approved use (to reduce the volume of total new heterotopic ossification in adults and pediatric patients 12 years and older with fibrodysplasia ossificans progressiva)? Summarize head-to-head and indirect evidence, efficacy, safety and where each fits, with citations.
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Safety signals
There is no boxed warning. The label lists embryo-fetal toxicity as the main warning, and the drug is contraindicated in pregnancy. Pregnancy status should be verified before starting in females of reproductive potential. Effective contraception is advised during treatment and for one week after the last dose. The most common adverse reactions (10% or more) were headache, arthralgia, upper respiratory tract infection, epistaxis, and nausea. Less common events included gastroenteritis, reflux, iron deficiency anemia, rash, and alopecia. Treated patients had mean increases in serum iron, hemoglobin, and transferrin saturation that stayed within the normal range. A separate pharmacokinetic study found higher drug exposure with moderate or worse renal impairment and with severe hepatic impairment.
What it competes with
Management of FOP centers on avoiding trauma and flare triggers, treating flare-ups symptomatically, and managing function over time. Targeted drugs that reduce heterotopic ossification are now available.
PalovaroteneOral retinoid-class agent used to reduce new heterotopic ossification in FOP. Its label carries safety concerns about premature growth plate closure in children.
GaretosmabAnti-activin A antibody under investigation for FOP; not an established alternative.
GlucocorticoidsShort courses are used to manage acute flare-ups, mainly for symptom control.
NSAIDs and analgesicsUsed for pain and inflammation during flares. They do not stop heterotopic bone formation.
Bottom line for clinicians
Atebrioz offers an oral option for patients 12 years and older with FOP who need to limit new heterotopic ossification. The pivotal trial was small, with 63 patients and 24 weeks of blinded follow-up, so long-term functional benefit is not established by these data. Weigh pregnancy risk and contraception needs, and note that exposure rises in renal and severe hepatic impairment.
Dosing, contraindications and full warnings are in the prescribing information.
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Last updated October 28, 2026 by 2 Minute Medicine.
For healthcare professionals. A summary of public FDA documents and published trials, not medical advice. Check the full prescribing information before prescribing.
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