Genentech Inc. and Biogen Idec Inc. shares slumped on Tuesday as the companies said their drug Rituxan failed a late stage trial to examine the efficiency of the drug in patients with lupus.

Shares of Genentech Inc. fell 7.2 percent or $5.23 to $67.93 at the closing of composite trading in the New York Stock Exchange today. Biogen's shares fell $3.34 or 5.16 percent to $61.33 at the end of the closing trading in Nasdaq.

We are disappointed in the results of this Phase II/III study, but we understood from the outset the significant challenges in developing treatments for systemic lupus erythematosus, said Genentech's senior vice president of development and chief medical officer Dr. Hal Barron, in a statement.

The companies said that any of the 257 patients with lupus that were involved in the trial showed clinical response that matched any of the aimed targets during a period of time of 52 weeks.

The drug is already approved to treat rheumatoid arthritis and non-Hodgkins lymphoma but the firms have been seeking to expand the use of the product that sold about $2.3 billion in 2007 in the United States. Earlier this month the firms reported another failure of Rituxan for treating primary progressive multiple sclerosis.

Genentech and Biogen are going through clinical trials to test Rituxan's effectiveness against lupus nephritis, expecting results by 2009.