UPDATE 3-US halts new enrollment in Glaxo's Avandia trial

* Current patients can continue in Tide trial

* FDA still weighing Avandia's future

* Glaxo shares almost unchanged amid broad stock losses (Adds analyst, consumer group comment; updates shares to NYSE close)

By Lisa Richwine

WASHINGTON, July 21 (Reuters) - U.S. health officials have halted enrollment of new patients in a clinical trial of GlaxoSmithKline Plc's (GSK.L) diabetes pill Avandia while regulators consider if the drug should stay on the market.

Diabetics already in the trial, known as Tide, may continue to participate, the Food and Drug Administration said in a statement on Wednesday.

The FDA will update the public on the trial once it completes a review of Avandia's risks, the agency said. An advisory panel last week voted 20-12 that Avandia sales could continue, although many panelists urged restrictions or new warnings about heart risks. [ID:nLDE66E07B]

Opponents are still pressing for the drug's withdrawal.

Dr. Sidney Wolfe, head of Public Citizen's Health Research Group, said the FDA was "failing to protect the public" by letting current patients stay in the study.

Leerink Swann analyst Seamus Fernandez said the decision to partially halt the trial provided little insight into the FDA's thinking on Avandia's fate.

The FDA is giving researchers time "to evaluate the ethical questions involved given the panel's votes," he said. "You can't really read into it."

Investors have worried Glaxo could face new legal liability if Avandia comes off the market, but many saw last week's vote as a sign the drug would remain available even if sales fall further. Britain-based Glaxo said last week it had settled most Avandia lawsuits. [ID:nLDE66E081]

The Tide trial was designed to compare the heart effects of Avandia to rival drug Actos from Takeda Pharmaceutical Co (4502.T). Critics say the study is unethical and should end. They say Actos is clearly safer and patients should not be exposed to a more dangerous medicine.

Glaxo, which has defended Avandia's safety, said it would suspend new patient enrollment in Tide and send a summary of recent safety data and the advisory panel's deliberations to researchers in the study.

"This pause in enrollment (in Tide) will give clinical trial investigators and patients time to learn about the data presented to the FDA advisory committee and the committee's recommendations," Dr. Ellen Strahlman, Glaxo's chief medical officer, said in a statement.

Researchers can use the data to update informed consent forms for current participants, the FDA said. Avandia opponents say the forms have not clearly explained possible risks.

More than 1,300 patients of a planned 16,000 are now enrolled, Glaxo spokeswoman Mary Anne Rhyne said.

Avandia, known generically as rosiglitazone, remains available for doctors to prescribe. The drug is approved for controlling blood sugar in patients with Type 2 diabetes, the most common form of the disease.

Avandia was once Glaxo's second-biggest drug at $3 billion a year until a 2007 study linked the pill to a higher risk of heart attacks. The drug's sales plunged to $1.18 billion in 2009, equivalent to 2.7 percent of Glaxo's group sales.

Debate about Avandia's safety has raged since the 2007 study. Other research has provided conflicting results and Glaxo says the overall evidence does not show Avandia increases the chances of a heart attack.

The FDA has not said when it will decide Avandia's future.

Glaxo's Strahlman said Avandia "is an important treatment option" for Type 2 diabetics and patients with questions should talk to their doctors.

Glaxo shares closed down one cent at $36.36 on the New York Stock Exchange, even as the ARCA Pharmaceutical Index .DRG shed 1.3 percent amid broad losses in stocks on worries about the health of the U.S. economy. (Reporting by Lisa Richwine. Editing by Robert MacMillan and Tim Dobbyn)