Regeneron Pharmaceuticals (NASDAQ: REGN) announced that the U.S. Food and Drug Administration has approved Pasatru (garetosmab-grts) to reduce the formation of new heterotopic ossification (HO) lesions and clinician-assessed flare-ups in adults with fibrodysplasia ossificans progressiva (FOP), according to a company press release.

FOP is an ultra-rare genetic disorder in which muscles, tendons, ligaments and other connective tissues are progressively infiltrated by abnormal bone formation. Approximately 900 people worldwide are diagnosed with FOP. Most patients are wheelchair-bound by age 30, and the median age of survival is 56.

The approval is based on results from the Phase 3 OPTIMA trial, which enrolled 63 adults with FOP. At 56 weeks, patients receiving the 10 mg/kg dose of Pasatru showed a 90% reduction in new HO lesions compared to placebo (2 lesions vs. 19 lesions), while those on the 3 mg/kg dose showed a 94% reduction (1 lesion vs. 19 lesions), as measured by CT scan. Clinician-assessed flare-ups numbered 9 in the 10 mg/kg group (an 88% reduction vs. placebo) and 53 in the 3 mg/kg group (a 15% reduction vs. placebo), compared to 66 in the placebo group. Changes in patient-reported flare-ups were not significantly different between treatment and placebo groups.

Serious treatment-emergent adverse events occurred in 2 patients in the 10 mg/kg group, 1 in the 3 mg/kg group, and 2 in the placebo group. The most common adverse reactions included abscess, acne, increased hair growth, madarosis, oral ulcers, nosebleeds, folliculitis, paronychia, and rash.

The recommended starting dose is 10 mg/kg given intravenously over 60 minutes once monthly, which may be reduced to 3 mg/kg if not tolerated. The drug can be administered in a range of care settings, including home infusion where appropriate.

Pasatru is a fully human monoclonal antibody that blocks Activin A, a protein Regeneron scientists identified as critical to HO development in FOP patients. A regulatory submission is currently under review by the European Medicines Agency, with additional submissions planned in Japan and other countries. A Phase 3 trial in adolescents and children, OPTIMA 2, is planned to begin later this year.