Shares of Wyeth tumbled 3.01 percent yesterday on news that the company faces generic competition to one of its top-selling drugs and that regulators were delaying approval of another medicine.

Teva Pharmaceutical Industries Ltd. announced it would sell a low-cost version of Wyeth's heartburn drug Protonix, its third-best-seller in 2006 with sales of $1.8 billion. For the first nine months of this year, the drug's sales rose 5 percent compared with the same period last year.

Separately yesterday, Wyeth said the Food and Drug Administration had again delayed Viviant, an experimental drug for preventing bone loss, so the agency can examine the risk of strokes and blood clots.

The company's stock fell $1.41 to close at $45.45 in a holiday-shortened session on the New York Stock Exchange. The shares were trading at more than $58 in May.

Wyeth's pharmaceutical division is based in Collegeville, Montgomery County, where it has 2,800 employees. The company is based in Madison, N.J.

Bernard Poussot, who becomes chief executive officer next Tuesday, said yesterday that Wyeth faced "revenue challenges" and would revise its earnings forecast in January.

Teva is an Israeli company with its North American headquarters in North Wales, Montgomery County.

"Teva has been actively building generic Protonix supply and, while the quantity of the supply is unknown, we are assuming it is a significant amount," said Jon LeCroy, an analyst at Natixis Bleichroeder in New York, in a note to clients. He cut his forecast for Wyeth's 2008 earnings 51 cents a share, to $3.52 a share.

Shares of Teva rose $1.31, or 2.90 percent, to $46.48 in Nasdaq trading yesterday.

A judge's Sept. 6 ruling allowed Teva to sell a low-cost version of Protonix before Wyeth's patent expires in 2010. Wyeth is appealing.

The firms have held settlement talks for months, and Wyeth did not expect Teva to go ahead with the introduction now, Poussot told investors in yesterday's conference call. Teva has agreed to halt shipments until Jan. 28 so talks can resume.

Wyeth has had three products delayed by the FDA this year, and the firm estimates their potential combined sales would be $4 billion a year. The latest, Viviant, was held up because the FDA wants more analyses and discussion of the risk of stroke and clotting in some patients. The agency also delayed the product last April, seeking additional data.

The FDA has not requested any new studies.