Cornerstone Therapeutics(Nasdaq: CRTX) is expanding its drug lineup by purchasing rights to an antibiotic product from a Massachusetts firm that filed for bankruptcy protection on Monday.

is paying $5 million plus royalties and the value of inventory for Factive from Oscient Pharmaceuticals. Factive treats chronic bronchitis.

In May, Cornerstone announced it was selling a controlling interest in the company to Italy-based Chiesi for $15 million.

"This transaction is reflective of our strategy to acquire, develop and commercialize prescription products for the respiratory market," said Craig Collard, Cornerstone’s chief executive officer. "Factive is a high-quality, patent-protected product with strong brand recognition. We believe that this product fits well within our existing portfolio and that our respiratory-focused sales force will be able to drive prescription growth of Factive in the U.S. market. Moreover, we remain positioned to evaluate additional drugs to add to our growing portfolio of products."

Factive produced some $16 million in 2009. It is covered by patents through 2018, Cornerstone said.

Oscient is based in Waltham, Mass.