UPDATE 2-FDA panel says data backs use of Glaxo's Promacta

(Adds Glaxo comments, background, byline)

By Debra Sherman

CHICAGO May 30 (Reuters) - An expert advisory panel to the U.S. Food and Drug Administration said on Friday that current clinical data supports short-term use of GlaxoSmithKline Plc's (GSK.L)(GSK.N) experimental platelet-boosting drug, Promacta, sending the drugmaker's shares higher.

Europe's biggest drugmaker is seeking U.S. approval for the drug, generically known as eltrombopag, as a short-term treatment for chronic idiopathic thrombocytopenia purpura (ITP), an autoimmune disease that reduces blood platelets crucial for blood clotting.

All 16 voting members said data supported its use short- term, defined as 6 weeks, which was the period studied.

Some panel members raised concerns the drug might be used longer term since ITP can be a chronic condition.

Long term risks include liver toxicity, bleeding following drug discontinuation and potential marrow fibrosis.

A comprehensive management program must be put in place to deal with certain risks, panel members agreed.

"We don't have a risk management program for other drugs that's as complicated as what we'd need for Promacta," Suzanne Berkman, senior drug management analyst at the FDA's Office of Surveillance and Epidemiology, told the panel. "There are multiple risks with Promacta."

Costs associated with restricting the use of the drug is a burden that should be paid for, at least in part, by the drug maker, some panel members said.

After the panel's vote, Dr. Debasish Roychowdhury, Glaxo's Vice President of Global Clinical Development, said in an interview the proposal was one "that should be discussed."

"It's a fair challenge," he added.

Glaxo shares were up 1.21 percent, or 53 cents, at $44.51 in afternoon trading on the New York Stock Exchange.

LABEL ISSUES

Dr. Richard Pazdur, director of the Office of Oncology Drug Products and Office in FDA, said he was not surprised by the panel's unanimous vote.

Pazdur said the panel had debated many of the same issues about safety and effectiveness when it discussed Amgen Inc's (AMGN.O) competing drug, Nplate, which is also awaiting FDA approval.

He added that labeling for Glaxo's product would still need to be negotiated. While the agency will make the final approval decision, it usually follows panel recommendations.

FDA approval of Promacta could help boost the British drugmaker, which sees the drug as a potential blockbuster in the face of dwindling sales of its older products. Some analysts have forecast Promacta's annual sales could top $1 billion.

While both drugs are designed to stimulate platelet production, Nplate is injected and is intended for long-term use, while Promacta is a pill and is intended for short-term use.

Current ITP treatments aim to decrease platelet destruction and can be toxic. Without enough platelets, patients are at risk for severe bleeding. While most cases can be controlled, the disease can be fatal in rare cases.

About 60,000 Americans have been diagnosed with the chronic form of the disease, according to Amgen.

Glaxo shares were closed up 0.5 percent in London. Glaxo discovered the drug in collaboration with Ligand Pharmaceuticals Inc (LGND.O). Ligand shares were up nearly 50 percent to $3.51 in afternoon trading on Nasdaq. (Additional reporting by Susan Heavey in Washington D.C.; Editing by Andre Grenon)