AstraZeneca falls on disappointing drug study

WASHINGTON (AP) -- Shares of AstraZeneca and its partner Rigel Pharmaceuticals Inc. fell Thursday after the companies reported that their experimental rheumatoid arthritis drug failed to show superiority to Abbott's Humira in a midstage study.

THE SPARK: AstraZeneca reported results for a six-month study of its drug fostamatinib in 280 patients with hard-to-treat rheumatoid arthritis. The drug met its first goal of showing superior results compared to a placebo after six weeks. But the study failed to achieve the second goal of showing it worked as well as Humira after six months of treatment.

THE BIG PICTURE: Humira, an injectable anti-inflammatory drug, is the world's best-selling rheumatoid arthritis treatment, with sales of roughly $9 billion a year. AstraZeneca and other large drugmakers have been working to develop rival treatments to compete with the blockbuster drug. The company's drug fostamatinib, licensed from Rigel, is a pill that blocks the protein kinase, which plays a role in a variety of inflammatory diseases.

AstraZeneca said the latest results should not be taken as definitive. The company is conducting a larger study of the drug's benefits which is expected to be completed in the first half of 2013. The company says those results will be the basis of its application to the Food and Drug Administration and other regulators.

SHARE ACTION: Shares of South San Francisco-based Rigel Pharmaceuticals Inc. fell $2.73, or 32.4 percent, to $5.70 in morning trading. U.S.-traded shares of AstraZeneca PLC fell $1.24, or 2.6 percent, to $47.66. Shares of Abbott Laboratories fell 74 cents, or 1.1 percent, to $65.27.