Rib-X Pharmaceuticals, a New Haven, Conn.-based biopharmaceutical company developing new antibiotics to treat serious and life-threatening infections, has closed the first tranche of a $67.5 million Series 2 preferred stock financing. A second tranche is anticipated to close around the end of 2012.

The round was led by new investor Vatera Healthcare Partners and included existing shareholders Warburg Pincus, ABS Ventures and Vox Equity Partners. Rib-X plans to use the proceeds to initiate the phase III clinical program for delafloxacin for the treatment of acute bacterial skin and skin structure infections (ABSSSI). Delafloxacin is being developed as a first-line therapy for use initially in hospitals prior to the availability of a specific diagnosis.

"The recently granted QIDP designation from the FDA means delafloxacin will receive priority review and is eligible for fast track status. Furthermore, if approved, this designation gives delafloxacin an additional five years of market exclusivity in the U.S.,” said Mark Leuchtenberger, CEO of Rib-X.

Dr. Thomas Koestler, executive director of Vatera Holdings, said, "We believe its broad spectrum activity and IV to oral potential give delafloxacin a strong market position and we look forward to working with the Rib-X management team to advance this important new antibiotic towards the market."