The FDA will hold a public meeting in July 2010 to discuss risks and benefits of the drug, but said in the meantime doctors and patients should continue to use Avandia as directed.

"This work is ongoing and no new conclusions or recommendations about the use of rosiglitazone (Avandia) in the treatment of type 2 diabetes have been made at this time," the FDA said, referring to the drug's generic name.

On Saturday, two U.S. senators released a report on Avandia and internal FDA documents. The documents included a 2008 memo from two FDA drug safety reviewers who recommended pulling the drug from the U.S. market after they concluded it was more dangerous to the heart than the rival drug Actos by Takeda Pharmaceutical Co Ltd.

One of the reviewers, FDA critic David Graham, had argued to an advisory panel in 2007 that Avandia should no longer be sold. That panel voted 22-1 to recommend the drug remain on the market.

Glaxo shares fell 2.5 percent to close at $37.32 on the New York Stock Exchange on Monday. Analysts said new attacks on Avandia could add to litigation risks and help rival drugmakers.

Sales of Avandia topped $3 billion in 2006, but fell to $1.2 billion in 2009.

The FDA said on Monday it is reviewing data from a Glaxo-sponsored study known as Record, as well as other studies that look at the cardiovascular safety of Avandia. The FDA will present all of the safety data at a public advisory panel meeting in July.

The FDA decided in November 2007 Avandia should carry a warning saying a review of 42 studies associated the drug with an increased risk of a heart attack or chest pain compared with a placebo. But it said overall data were "inconclusive."

"We don't find that available information since that time has really changed the assessment," Dr. Janet Woodcock, head of the FDA's drugs center, said on a conference call with doctors on Monday.

Woodcock added, "We feel that it is time for a thorough re-evaluation of all the data of the drug as far as cardiovascular risk, and we are undertaking that right now."