What is FOP
Fibrodysplasia ossificans progressiva, or FOP, is one of the rarest diseases in the world. It affects about one in a million people. In patients with FOP, the body grows bone in places where bone should not exist, such as muscles, tendons and ligaments. Over time, this extra bone locks joints and can leave a person unable to move.
The disease usually appears in childhood. Flare-ups, often triggered by injury or illness, cause swelling and pain and lead to new bone formation. There is no cure.
How Pasatru works
The FDA approved Pasatru (garetosmab-grts) on Wednesday to reduce the formation of new bone lesions and disease flare-ups in adults with FOP. It is made by Regeneron.
Pasatru is a fully human monoclonal antibody. It binds to and neutralizes activin A, a protein that Regeneron scientists discovered plays a central role in driving the abnormal bone growth. The drug is given as an intravenous infusion over 60 minutes once a month. The recommended starting dose is 10 mg per kilogram of body weight, which can be lowered to 3 mg/kg if a patient does not tolerate it.
What the trials showed
In the phase 3 OPTIMA trial, adults who received monthly infusions of Pasatru showed up to a 94 percent reduction in new heterotopic ossification lesions compared with those on placebo. Common side effects included nosebleeds, abscesses, acne, increased hair growth, mouth ulcers and rashes.
Pasatru is the second drug approved for FOP. The first, palovarotene (Sohonos), was approved in 2023 for adults and children. Regeneron said a new trial, called OPTIMA-2, will test Pasatru in children and adolescents.