Emergent BioSolutions Inc said the U.S. Food and Drug Administration approved its treatment for inhaled anthrax, triggering a $7 million milestone payment from the U.S. Department of Health and Human Services (HHS).

Emergent Bio developed the treatment, Anthrasil, as part of a $160 million contract it signed in 2005 with the Biomedical Advanced Research and Development Authority (BARDA), a part of the HHS.

The drug is already being stored in the U.S. Strategic National Stockpile, the company said on Wednesday.

Anthrasil is a sterile solution of purified human immune globulin G (IgG) that targets the anthrax toxins of Bacillus anthracis, the bacteria that causes anthrax disease.

It has been approved for use in combination with other antibacterial drugs.

Anthrasil is made using plasma from healthy, screened donors who have been immunized with Emergent Bio's Anthrax vaccine, BioThrax, the only FDA-licensed vaccine for the disease.

Earlier this week, the HHS signed a $31 million agreement with Maryland-based Emergent Bio to develop a vaccine that requires only two doses to confer immunity.

Biothrax currently needs three doses.