The bestselling medicine for two of the country's biggest biotech drug companies has been further linked to a rare and deadly brain infection, U.S. health officials warned Monday.
The news could hurt efforts by Genentech Inc. and Biogen Idec Inc. to expand approved treatments for Rituxan.
Patients taking Rituxan, a drug approved to treat rheumatoid arthritis and non-Hodgkins lymphoma, have been known to contract the rare brain infection. But two patients being treated for lupus also have died from the infection after taking Rituxan, the Food and Drug Administration said in a notice posted on its website.
The two deaths are the first ones reported for so-called off label uses for Rituxan. Doctors often prescribe a drug for diseases other than those for which it is approved if they believe it may help with similar symptoms. Systemic lupus erythematosus, or SLE, is an autoimmune disease that causes arthritis, among other things.
The news comes as Genentech and Biogen seek to expand approved treatments for Rituxan, including lupus. The drug is their biggest seller, with $1.8 billion in sales nationwide last year. It is illegal for drug makers to promote off-label uses, but doctors can use their judgment.
"This might make it more challenging to develop Rituxan" for other diseases, Eric Schmidt, an analyst with Cowen & Co. in New York, told Bloomberg News. "Even though we can't necessarily link this to Rituxan, it's an unfortunate circumstance."
The link between Rituxan and the brain infection, called progressive multifocal leukoencephalopathy, or PML, is not clear, but 23 rheumatoid arthritis and lymphoma patients have contracted the brain illness while or shortly after being treated with Rituxan, Genentech spokeswoman Debra Charlesworth said.
PML usually is fatal, and there is no treatment.
More than a million patients have been treated with Rituxan since the drug was approved in 1997, Charlesworth said.
The virus that causes PML is present in 80% of adults but is dormant, the FDA said. It is not clear whether the virus is triggered by Rituxan, which suppresses a patient's immune system, or by the diseases it is supposed to treat.
Rituxan's prescribing instructions already include information about reports of viral infections, including PML.
Genentech and Biogen estimated that about 10,000 SLE patients were treated with Rituxan.
The news was announced after the markets closed Monday. Shares of South San Francisco-based Genentech rose 17 cents to $80.96 in regular trading and fell $1.46 to $79.50 after hours.
Cambridge, Mass.-based Biogen shares fell $1.13 to $50.23 in regular trading and dropped $2.69 in extended trading.