Amgen Inc drug Nplate is safe and effective for treating a rare clotting disorder that can cause dangerous bleeding, the Food and Drug Administration said on Friday in approving the product for U.S. sales.

The injectable drug helps stimulate bone marrow into producing blood platelets in patients with chronic immune thrombocytopenic purpura (ITP), the FDA said. The agency approved its use for patients only after other available treatments fail to help.

“This product is important in that it offers a new approach to the treatment of patients with an uncommon blood disorder who are often very ill,” said Dr. Janet Woodcock, head of the FDA’s Center for Drug Evaluation and Research.

Other approved ITP treatments include steroids, immune-suppressing drugs or surgery to remove the spleen.

“Until now there have been limited FDA-approved treatments available to patients suffering from chronic adult ITP, and the treatment options were often unsuccessful for long-term use,” Amgen said in a statement.

The total cost of care for Nplate patients is expected to be “less than or comparable to the total costs of care with standard treatment regimens,” the Thousand Oaks, California-based biotech company said.

Patients who still had their spleen fared better than those who did not, it added.

ITP occurs when the immune system destroys platelet cells that help the blood clot and low platelet levels can trigger life-threatening bleeding. Patients with the condition are also more likely to experience bruising.

Nplate, also known as romiplostim, is not expected to be a big seller and also faces competition. About 60,000 U.S. adults have chronic ITP, Amgen has said.

Some analysts expect it to earn anywhere from $66 million to $117 million in 2009 sales and peak around $200 million — small compared with Amgen’s 2007 revenue of $14.7 billion.

GlaxoSmithKline Plc’s rival drug, Promacta, or eltrombopag, faces an FDA approval decision by September 19.

Amgen’s shares were largely unaffected by the FDA’s decision, in part because the ruling had initially been expected in July before the agency postponed it.

Analysts have instead been buoyed by hopes for its experimental osteoporosis drug called denosumab, which is still in development.

“We are encouraged by the approval, but note that the small patient market for this drug will result in a modest contribution to the company’s revenues,” William Blair & Co analysts said in a research note.

“We continue to believe that the most meaningful revenue addition for Amgen will be pending approval of denosumab in osteoporosis,” they wrote.
Both Amgen and Glaxo shares closed up less than 1 percent on the Nasdaq and the New York Stock Exchange, respectively.

The company said it was seeking additional approval for Nplate in Europe, Canada and Switzerland. Australian authorities approved the drug last month.