On March 30, 2015, the FDA approved the use of Neupogen (filgrastim) to treat adult and pediatric patients acutely exposed to myelosuppressive doses of radiation (Hematopoietic Syndrome of Acute Radiation Syndrome, or H-ARS). 

Myelosuppression occurs when radiation damages internal organs, including bone marrow. Suppression of the bone marrow blocks the production of blood cells. Neupogen can help patients with H-ARS by facilitating recovery of bone marrow cells that develop into white blood cells, including neutrophils, that help fight off infections.

Neupogen is the first FDA-approved medical countermeasure to increase survival in patients exposed to myelosuppressive doses of radiation. It was approved by FDA based on studies in animals (under the Animal Rule), as studies in humans could not be ethically conducted.

For more details, go to: http://www.fda.gov/EmergencyPreparedness/Counterterrorism/MedicalCountermeasures/AboutMCMi/ucm443245.htm