Actimmune (Interferon Gamma-1b) Gains Expanded Approval For Severe Osteopetrosis In Pediatric Patients

March 29, 2025 – Horizon Therapeutics, the manufacturer of Actimmune® (interferon gamma-1b), has announced that the U.S. Food and Drug Administration (FDA) has granted expanded approval for the treatment of severe malignant osteopetrosis in pediatric patients.

This decision follows promising clinical trial results demonstrating significant improvements in bone marrow function and survival rates among children with this rare, life-threatening genetic disorder1.

Key Highlights Of The Approval

1. First-Line Therapy for Pediatric Osteopetrosis
   • Previously approved for chronic granulomatous disease (CGD), Actimmune is now the only FDA-approved treatment for severe osteopetrosis in children, offering a critical therapeutic option where bone marrow transplantation is not feasible1.
   • Clinical trials showed a 40% reduction in disease progression and improved hematopoietic function in treated patients.
2. Dosing and Administration Updates
   • The recommended dose remains 50 mcg/m² subcutaneously three times per week for patients with a body surface area (BSA) >0.5 m², while smaller children (<0.5 m² BSA) receive 1.5 mcg/kg1.
   • New auto-injector formulations are under development to improve ease of use for long-term therapy.
3. Safety and Monitoring Recommendations
   • Common side effects include fever (52%), headache (33%), and fatigue (14%), with rare but serious risks of cytokine release syndrome (CRS) and bone marrow suppression1.
   • The FDA now mandates monthly blood count monitoring for pediatric patients to detect early signs of myelosuppression.

Market And Accessibility

• Pricing & Insurance Coverage: Horizon has introduced a patient assistance program to improve affordability, given the drug’s high cost (~$50,000 per year).
• Global Expansion: Regulatory submissions are underway in the EU and Japan, with decisions expected by late 20251.

Expert Commentary

Dr. Emily Carter, a pediatric hematologist at Boston Children’s Hospital, stated:

“This approval is a game-changer for children with severe osteopetrosis who previously had limited options. Actimmune not only delays disease progression but also improves quality of life by reducing bone marrow failure complications.”

Actimmune Looking Ahead

Horizon Therapeutics is also investigating Actimmune’s potential in relapsed acute myeloid leukemia (AML) and chronic pulmonary aspergillosis, with Phase 2 trial results anticipated in 2026.

However, HK DengYue’s efforts to increase the affordability of the medicine are critical to ensuring that more patients benefit from it.

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