Idenix Pharmaceuticals Inc. priced its public offering worth $150 million to build its working capital and fund research and development activities related to its infectious disease drug candidates.

The Cambridge, Mass.-based company is selling about 7.3 million shares of its common stock at a price of $20.61 per share. More than half of those shares, about 3.9 million, are being offered to its partner, Novartis AG, which holds 57 percent of Idenix's outstanding shares. If Novartis purchases those shares, it would maintain a 56 percent ownership in Idenix. Novartis initially purchased more than half of Idenix's outstanding shares in 2003 when the companies signed a potential $862 million deal.

Idenix was unable to comment due to SEC-imposed quiet-period rules. In its prospectus, it estimated that net proceeds would total about $145.5 million. The funds also will be used for general corporate purposes, building a commercial operations infrastructure and for potential acquisitions of new businesses, technologies or products.

Shares of Idenix (NASDAQ:IDIX) gained 18 cents Wednesday to close at $20.79.

The company has an ongoing Phase III program for its hepatitis B drug, telbivudine. In late July, the company reported top-line data from the trial showing that the compound reached its one-year primary efficacy endpoint. The drug demonstrated non-inferiority when compared to lamivudine, sold by London-based GlaxoSmithKline plc as Combivir in the 1,350-patient study. A new drug application is expected to be submitted during the first part of 2006 based on the first year data, though the trial will continue for another year.

Telbivudine is partnered with Basel, Switzerland-based Novartis, stemming from the 2003 collaboration. In exchange for acquiring 51 percent of Idenix, Novartis paid about $255 million, and provided an up-front fee of $75 million for licensing rights to the hepatitis B portfolio, which included telbivudine. Novartis also covered development costs and agreed to handle all regulatory filings outside the U.S. (See BioWorld Today, March 27, 2003.)

The agreement also provided an option for Novartis to license a then-preclinical compound for hepatitis C virus, NM283 (valopicitabine). Following the completion of Phase II, Novartis will be able to decide whether to license the compound for a potential $525 million, including clinical and regulatory milestones.

In addition to shares offered by the company, Idenix's shareholders are offering 942,507 shares and are granting underwriters an overallotment option of 1.1 million shares. Idenix will not receive proceeds from either of those transactions.

New York-based Morgan Stanley & Co. acted as the sole bookrunner, and Bear, Stearns & Co., also of New York, served as co-lead manager for the offering.