GlaxoSmithKline's diabetes pill Avandia should stay on the the market even though data suggest it may raise the risk of a heart attack for some patients, US advisers said.

Most of the advisory panel said the Food and Drug Administration should ask for strong new warnings on the widely used drug, but evidence was too thin to justify halting sales.

Data "does suggest there is an increased risk," said Dr Clifford Rosen, the panel's chairman.

After hearing various analyses of a mass of data, the panel voted 20-3 that Avandia may increase the chances of having a heart attack for some patients. Members voted 22-1 that Avandia should stay on the market.

Glaxo shares rose 5.2 percent in extended US trading to $52 from their close of $49.43 on the New York Stock Exchange.

Millions of diabetics around the world take Avandia, Glaxo's second-best-selling drug. Its safety came into question in May, when a Cleveland Clinic analysis linked Avandia to a 43 percent higher chance of having a heart attack.

Glaxo and senior FDA officials said other evidence conflicted with that finding.

The advisory panel felt certain diabetics face greater heart risks than others, Rosen said. They include patients with heart failure or significant cardiovascular disease, or diabetics taking nitrates or insulin.

Some urged a "black box" warning on Avandia, the strongest type of warning for prescription drugs.

The FDA usually adopts the recommendations of advisory panels, which are groups of experts from outside the agency.

Inside the FDA, officials have been split about how to deal with Avandia. Outspoken FDA scientist David Graham said he saw a higher heart attack risk and no advantage over alternatives.

Takeda Pharmaceutical Co. Ltd.'s rival drug, Actos, did not appear to carry the same risk, Graham said.

His boss, Dr Gerald Dal Pan, agreed, and both said they felt the drug should come off the market. Dal Pan runs the FDA office that monitors side effects after a drug's approval.

Other officials in the division that approves drugs for sale told the panel they were unsure how risky Avandia was and were seeking the panel's advice.

About 21 million Americans have type 2 diabetes, a disease in which the body does not adequately control blood sugar. Patients are at risk for heart disease, kidney failure, limb amputation and other serious complications.

Glaxo said Avandia was a valuable option because many patients need multiple drugs to keep blood sugar under control, and a portion of them cannot take some of the other therapies.

"We still maintain our position that we had all along that there is no difference" in heart attack risk when Avandia is compared to other diabetes pills, Chris Viehbacher, Glaxo's president of US pharmaceuticals, said in an interview after the panel meeting.

 The safety controversy has hurt Avandia sales. Worldwide sales in the three months to June dropped to 349 million pounds from 477 million a year ago, the company reported last week.

Takeda said following the panel decision that the company underscored its position that Actos offers a proven safety profile.

"Short- and long-term studies, both prospective and observational studies in both humans and animals have shown no evidence that Actos is associated with an increased risk of heart attack or stroke," Mehmood Khan, president of Takeda Global Research and Development, said in a statement.

Mehta Partners analyst Shaojing Tong said the panel decision was "somewhat more positive for Actos" as doctors may still have a muddled view of Avandia.

"Doctors' views have been not so clear and going forward it's not going to be so clear," Tong said.

Avandia is known generically as rosiglitazone, while Actos is known as pioglitazone. Both drugs are so-called thiazolidinediones that were designed to make the body more s