Pasatru

Pasatru (garetosmab-grts) is a prescription medicine used to reduce new abnormal bone growth in muscles, tendons, ligaments, and other connective tissues, and to reduce flare-ups in adults with fibrodysplasia ossificans progressiva (FOP).

People with FOP have an ultra-rare genetic disorder that results in a specific protein called Activin A triggering new bone formation within soft tissue. Pasatru works by binding to activin A, blocking abnormal bone growth signaling to help slow down new abnormal bone formation and the progression of FOP.

Pasatru is a fully human monoclonal antibody that acts as an activin signaling inhibitor.

It is given as an intravenous (IV) infusion over 60 minutes, once every 4 weeks, by a healthcare provider. Depending on the care setting, this may include home infusion where appropriate.

Yes, Pasatru was approved by the FDA on August 19, 2026, following positive results from the Phase 3 OPTIMA placebo-controlled trial, which demonstrated reductions in both new HO lesions and clinician-assessed flare-ups in adults with FOP.

Pasatru is FDA-approved for adults with fibrodysplasia ossificans progressiva (FOP) to:

• reduce the formation of new heterotopic ossification (HO) lesions
• reduce clinician-assessed flare-ups

It is not known if Pasatru is safe and effective in children.

Pasatru must not be used during pregnancy.

Fibrodysplasia ossificans progressiva (FOP) is an ultra-rare genetic disorder in which muscles, tendons, ligaments and other connective tissues are progressively replaced by bone, a process called heterotopic ossification (HO).

HO affecting the jaw, spine, hip and rib cage can make speaking, eating, walking or breathing difficult, and loss of function in these areas leads to escalating loss of mobility.

FOP is caused by gain-of-function mutations in activin receptor type 1 (ACVR1, also called ALK2), a bone morphogenetic protein (BMP) type I receptor. In the Pasatru clinical trial, 95% of participants had the R206H mutation, the most common FOP-causing variant.

Pasatru works by blocking activin A, the protein that switches on the faulty ACVR1 receptor responsible for abnormal bone growth in FOP.

In people with FOP, the mutated ACVR1 receptor is abnormally activated by activin A, which triggers heterotopic ossification. Garetosmab-grts, the active ingredient in Pasatru, is a human IgG4 monoclonal antibody that binds to activin A and inhibits its signaling. This blocks activation of the FOP-mutant ACVR1 receptor and reduces the formation and progression of new heterotopic bone lesions.

Pasatru is given by a healthcare provider as an intravenous (IV) infusion into a vein over 60 minutes, once every 4 weeks.

• Pasatru is prepared and administered by a healthcare professional using an infusion pump.
• It can be given in a range of care settings, including home infusion where appropriate.
• Your healthcare provider will confirm you are not pregnant before your first dose if you are a female of reproductive potential.

What if I miss a dose of Pasatru?

If you miss an infusion appointment, call your healthcare provider as soon as possible to reschedule. The missed dose should be given as soon as possible, and your next infusion will then be scheduled every 4 weeks from the date of that dose.

Pasatru must not be used during pregnancy

Pasatru is contraindicated in pregnancy and can cause serious birth defects. Based on how it works and on animal reproduction studies, Pasatru can cause fetal harm when given to a pregnant woman.

For females who can become pregnant:

• your healthcare provider will organise a pregnancy test to confirm you are not pregnant before you start Pasatru
• use effective birth control (contraception) during treatment and for 6 months after your last dose
• if you become pregnant or think you may be pregnant during treatment, stop Pasatru immediately and contact your healthcare provider right away

Skin and soft tissue infections

Skin and soft tissue infections requiring treatment or hospitalization, including abscesses and cellulitis, have occurred in patients receiving Pasatru in clinical trials. Report signs or symptoms of skin infection, such as redness (erythema), pain, swelling or fever, to your healthcare provider and seek medical attention if these occur.

Epistaxis (nosebleeds)

Spontaneous nosebleeds, including serious cases requiring medical attention, have been reported in patients receiving Pasatru. In clinical trials in FOP, one serious case required hospitalization for nasal packing and application of a clotting agent.

Seek medical attention for a nosebleed that is severe, prolonged (for example, lasting more than 20 minutes), and does not stop with standard first-aid measures.

Tell your healthcare provider about all your medical conditions, including if you:

• are pregnant or could become pregnant. Pasatru must not be used during pregnancy.
• are breastfeeding or plan to breastfeed. Breastfeeding is not recommended during treatment with Pasatru and for 6 months after the last dose.
• are concerned about male fertility. Pasatru may affect your ability to father a child.

Tell your healthcare provider about all the medicines you take, including prescription and over-the-counter medicines, vitamins and herbal supplements.

Pregnancy

Pasatru is contraindicated during pregnancy and can cause fetal harm, including serious birth defects. Pregnancy must be ruled out before treatment starts, and females of reproductive potential should use effective contraception during treatment and for 6 months after the last dose.

Monoclonal antibodies can cross the placenta, and transfer increases as pregnancy progresses, peaking in the third trimester. Pasatru may therefore be present in infants exposed in the womb, and the potential effects on those infants should be considered.

Breastfeeding

Breastfeeding is not recommended during treatment with Pasatru and for 6 months after the last dose.

There are no data on whether Pasatru passes into human or animal milk, or on its effects on a breastfed infant or on milk production. Maternal IgG antibodies are known to be present in human milk. The recommendation reflects the potential for serious reactions in a breastfed infant, including skin and soft tissue infections, and possible effects on male reproductive organ development.

Male fertility

Based on findings from animal studies, Pasatru may impair male fertility. In a 26-week study in sexually mature monkeys, minimal to moderate seminiferous tubule degeneration was seen, which reversed after a treatment-free recovery period; sperm concentration, sperm motility and testosterone levels were unchanged. In 5-week studies in male rats, garetosmab-grts caused inflammation, granulomas and epithelial degeneration in the male reproductive tract with decreased sperm motility at exposures below the recommended human doses.

Talk to your healthcare provider if fathering a child is a concern for you.

Children and older adults

The safety and effectiveness of Pasatru have not been established in children. Clinical studies did not include enough patients aged 65 years and older to determine whether they respond differently from younger adults.

Common Pasatru side effects

The most common Pasatru side effects are abscess (infected lump), acne, increased hair growth, loss of eyebrows or eyelashes (madarosis), mouth sores (oral ulcers), and nosebleeds (epistaxis). These side effects were reported in 10% or more of adults with FOP in clinical trials.

Infected hair follicles (folliculitis), nail infection (paronychia), and rash were also reported in 10% or more of patients in at least one Pasatru dose group.

Serious Pasatru side effects

Pasatru can cause serious side effects, including harm to an unborn baby, skin and soft tissue infections, and severe nosebleeds. See the warnings section for more detail.

Call your healthcare provider right away if you have:

• signs or symptoms of a skin infection, such as redness, skin that feels warm to the touch, swelling, pain or tenderness, fever, or feeling generally unwell
• a nosebleed that is severe or heavy, does not stop with basic first aid such as pinching the nose with continuous firm pressure, or lasts more than 20 minutes

If you become pregnant or think you may be pregnant during treatment, stop Pasatru immediately and call your healthcare provider right away.

This is not a complete list of side effects, and others may occur. Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

In the Phase 3 OPTIMA trial, Pasatru reduced new abnormal bone growth by 90% to 94% over 56 weeks compared with placebo in adults with FOP.

New heterotopic ossification (HO) lesions were measured by whole-body CT scan at 56 weeks:

• Pasatru 10 mg/kg: 2 new lesions in total, a 90% reduction compared with placebo

• Pasatru 3 mg/kg: 1 new lesion in total, a 94% reduction compared with placebo

• Placebo: 19 new lesions in total

Both reductions were statistically significant.

Most patients on Pasatru developed no new bone lesions at all. New lesions occurred in 9% of patients on 10 mg/kg and 5% of patients on 3 mg/kg, compared with 24% of patients on placebo.

Flare-ups

The number of clinician-assessed flare-ups through Week 56 was 9 with Pasatru 10 mg/kg, 53 with Pasatru 3 mg/kg, and 66 with placebo. The rate ratio compared with placebo was 0.12 (95% CI: 0.03 to 0.42) for the 10 mg/kg dose, and 0.85 (95% CI: 0.26 to 2.73) for the 3 mg/kg dose.

Changes in the proportion of patients with patient-reported flare-ups through Week 56 were not significantly different between the placebo and Pasatru groups.

Volume of new bone

The mean volume of new HO at Week 56 was 10.5 cm³ with placebo, 0.02 cm³ with Pasatru 10 mg/kg, and 0.01 cm³ with Pasatru 3 mg/kg. These differences were not statistically significant based on the pre-specified statistical test.

About the OPTIMA trial

OPTIMA (NCT05394116) was a randomized, double-blind, placebo-controlled, multicenter Phase 3 trial in 63 adults with FOP confirmed by an ACVR1 FOP-causing mutation. Participants received Pasatru 10 mg/kg, Pasatru 3 mg/kg or placebo intravenously every 4 weeks for 56 weeks, then continued their originally assigned treatment in a double-blind extension phase.

Participants had a median age of 25 years (range 18 to 42), 60% were female, and the mean baseline Cumulative Analog Joint Involvement Scale (CAJIS) score was 13 on a scale of 0 to 30, where higher scores indicate greater disease severity.

A Phase 3 trial of Pasatru in adolescents and children with FOP, OPTIMA 2, is planned to begin later this year.

Recommended Pasatru dosage for adults with FOP

• Starting dosage: 10 mg/kg given as an intravenous infusion over 60 minutes, once every 4 weeks.
• If 10 mg/kg is not tolerated: the dosage may be decreased to 3 mg/kg given as an intravenous infusion over 60 minutes, once every 4 weeks.

Pasatru dosage is based on body weight, so the amount given is calculated individually for each patient.

Pasatru strengths

Pasatru is supplied as a 300 mg/5 mL (60 mg/mL) solution in a single-dose vial. Each vial is for one-time use only.

Pasatru is a specialty infusion medicine, and your out-of-pocket cost will depend on your insurance coverage, the infusion setting, and any patient support you qualify for.

Regeneron's myRARE program offers resources for people living with rare diseases and their healthcare providers, including product information, insurance benefit verification and information about potential financial support.

No drug interaction studies have been conducted with Pasatru.

Tell your healthcare provider about all the medicines you take, including prescription and over-the-counter medicines, vitamins and herbal supplements.

Pasatru should not be mixed with other drugs, and other drugs should not be given at the same time through the same infusion line.

• Store the unopened vial in a refrigerator at 2°C to 8°C (36°F to 46°F) in the original carton to protect it from light.
• Do not freeze.
• Do not shake.

Pasatru is normally stored and prepared by the healthcare professional or pharmacy supplying your infusion.

Active ingredient: garetosmab-grts

Inactive ingredients: arginine hydrochloride, histidine, L-histidine hydrochloride monohydrate, polysorbate 20, sucrose, and Water for Injection, USP.

Garetosmab-grts is a human IgG4 monoclonal antibody produced by recombinant DNA technology in Chinese hamster ovary cell suspension culture, with an approximate molecular weight of 146 kDa. Pasatru injection is a sterile, preservative-free solution with a pH of 6.3.

Pasatru is manufactured by Regeneron Pharmaceuticals, Inc., a biotechnology company based in Tarrytown, New York.