Shares of Idenix Pharmaceuticals Inc. continued to fall Wednesday in pre-market trading, a day after the drug developer said it was revising its collaboration agreement with the Swiss pharmaceutical company Novartis.

Idenix, based in Cambridge, Mass., said late Tuesday it will no longer receive royalty or milestone payments from Novartis, an Idenix shareholder, based on sales of the hepatitis B treatment Tyzeka. It also said it agreed to pay Novartis a royalty based on worldwide sales of future Idenix hepatitis C drugs unless they are used in combination with Novartis treatments.

The companies also ended an option right of Novartis to license Idenix current and future-stage drug candidates in any therapeutic area.

Hepatitis C is a virus that can lead to life-threatening liver damage and is the main cause of liver transplants in the United States. Analysts see treatments for the virus as being potentially lucrative for drugmakers because they see the virus as a growing health problem.

The development and collaboration agreement between the companies dates back to May 2003.

Idenix said Tuesday the revision gives it more flexibility to optimize the value of its pipeline.

The drug developer also said it had started a $150 million public offering of stock. It plans to use proceeds for research and development expenses, among other things. Stock offerings typically pressure share price as well, because additional shares dilute earnings for existing investors.

Idenix shares fell 8 percent, or 89 cents, to $10.13 yesterday while the Dow Jones industrial average edged down slightly. The stock slid another 5.9 percent, or 60 cents, to $9.53 Wednesday in premarket trading.