Optimer Pharmaceuticals Inc. filed for an initial public offering, hoping to raise $86 million to fund late-stage development and commercialization of its two anti-infectives, difimicin and prulifloxacin.

The San Diego-based firm, which is seeking a Nasdaq listing under the ticker symbol "OPTR," has not yet set the price or number of shares to be offered.

While the IPO market has been more open to biotech firms during the last few years, those initial offerings continue to price lower than expected. Through the end of October, 25 firms have gone public this year, according to BioWorld Financial Watch, with an average of $44.1 million raised.

In its prospectus, Optimer anticipates using a portion of the proceeds to complete a Phase II/III trial and a second Phase III trial of difimicin, a fast-track antibiotic aimed at Clostridium difficile-associated diarrhea (CDAD), a hospital-acquired infection that, in serious cases, can result in death. The company partnered difimicin with Par Pharmaceutical Inc., of Spring Valley, N.Y., in 2005, in exchange for an equity investment.

Optimer also expects sufficient funds to complete Phase III trials of prulifloxacin, an antibiotic for travelers' diarrhea. The first of those already is ongoing, with expected enrollment of 375 patients at sites in the U.S., Mexico and Peru. A second Phase III trial, expected to begin this quarter, will enroll 250 patients in the Dominican Republic, India and Thailand.

Optimer gained U.S. rights to prulifloxacin from Kyoto, Japan-based Nippon Shinyaku Co. Ltd. in 2004. The product has been sold in Japan since 2002.

Beyond its lead products, Optimer is developing additional candidates using its One-Pot Synthesis (OPopS) drug discovery platform, a computer-aided method of synthesizing carbohydrate-based compounds, with the goal of out-licensing them to partners.

The company already entered a deal with start-up firm Cempra Pharmaceuticals Inc., of Morrisville, N.C., for the preclinical compounds OPT-1068 and OPT-1273 for respiratory tract infections. Terms of that agreement, signed in January, called for Optimer to receive an equity position in Cempra, plus milestones and royalties on any commercialized products. (See BioWorld Today, April 14, 2006.)

The OPopS platform also yielded potential treatments for areas outside the antibiotic space, including breast cancer and osteoarthritis.

Optimer reported a net loss of $5.7 million for the six months ending June 30. At that time, the company had cash and cash equivalents totaling $25.9 million. Its last financing, a Series D round, closed last year and brought in $22.2 million.

Prior to the IPO, the company's principal stockholders include: Par Pharmaceutical Inc., which holds 5 million shares, or 15.5 percent; Formosa Healthcare Investments LP, with 2.8 million shares, or 8.5 percent; Princeton, N.J.-based ProQuest Investments II LP, with 2.6 million shares, or 7.9 percent; Boston-based BB Biotech Ventures II LP, with 2.2 million shares, or 6.8 percent; and individual investor Chi-Huey Wong, who holds 2.2 million shares, or 6.7 percent.

New York firms Piper Jaffray & Co. and Jefferies & Co. Inc. are acting as joint book-running managers for the offering, with JMP Securities LLC and Rodman & Renshaw LLC serving as co-managers.

In other financing news:

• Metabolix Inc., of Cambridge, Mass., a company focused on developing environmentally sustainable alternatives to petrochemical-based plastics, fuels and chemicals, priced its IPO of 6.8 million shares at $14 each to raise $95.2 million, more than the $86 million projected in its July filing. Metabolix also granted underwriters a 30-day option to purchase up to an additional 1 million shares to cover any overallotments. The company expects to invest net proceeds in pilot manufacturing and commercial formulation of Natural Plastic and to fund working capital needs, including pre-commercial manufacturing and marketing activities, research and development in its switchgrass biorefinery program, hiring additional personnel and for other research and development and general corporate purposes. Piper Jaffray & Co. is acting as book-running manager, while Jefferies & Co., Thomas Weisel Partners LLC and Ardour Capital Investments LLC, all of New York, are serving as co-managers. On the first day of trading, Metabolix's shares (NASDAQ:MBLX) gained $1.52 to close at $15.52.