Jan. 28 (Bloomberg) -- Merck & Co. said the U.S. Securities and Exchange Commission has started a formal probe into its handling of Vioxx, the painkiller pulled from the market Sept. 30 because of its link to heart attacks and strokes.

The SEC's decision wasn't unexpected, the Whitehouse Station, New Jersey-based company said in a statement today. A formal probe gives the SEC staff the power to issue subpoenas for documents or testimony.

Merck wouldn't comment on the SEC matter beyond the press release, company spokesman Tony Plohoros said. SEC spokesman John Heine declined to comment on the investigation. Merck shares fell as much as 9.2 percent.

Vioxx may have caused as many as 140,000 heart attacks in the U.S. between its 1999 introduction and the recall, Food and Drug Administration safety reviewer David Graham said in a study published this week by the U.K. medical journal Lancet. As of Dec. 31, Merck said 575 lawsuits had been filed by 1,400 plaintiffs' groups alleging injuries linked to Vioxx, including heart attacks and kidney damage.

The Department of Justice and certain Congressional committees also are conducting probes.

Merck shares dropped $2.53, or 8 percent, to $28.65 after falling as low as $28.32. Earlier today, a U.S. appeals court invalidated the company's patent for a once-a-week version of its osteoporosis drug Fosamax, opening the door to generic competition beginning in 2008.

To contact the reporter on this story: Kerry Dooley in Washington at kdooley@bloomberg.net.

Last Updated: January 28, 2005 12:24 EST