Idenix prices underwritten registered public offering of 18 million shares of common stock

Idenix Pharmaceuticals, Inc. (Nasdaq: IDIX), a biopharmaceutical company engaged in the discovery and development of drugs for the treatment of human viral diseases, today announced the pricing of an underwritten registered public offering of 18,310,000 shares of its common stock at a public offering price of $2.80 per share. All of the shares are being sold by Idenix. The offering is expected to close on April 13, 2011, subject to customary closing conditions.

J.P. Morgan Securities LLC is acting as sole book-running manager and underwriter for the offering. Idenix has granted the underwriter a 30-day option to purchase up to an additional 2,746,500 shares to cover over-allotments, if any.

The shares will be issued pursuant to a shelf registration statement on Form S-3 previously filed with and declared effective by the Securities and Exchange Commission. Idenix will also file with the Securities and Exchange Commission a prospectus supplement with respect to the offering.