The agency says a woman died of the rare viral infection more than a year and a half after discontinuing the drug, which is used to treat rheumatoid arthritis and non-Hodgkin’s lymphoma, and is marketed in the US by Genentech and Biogen Idec.

Although cases of the infection have previously been reported in patients taking Rituxan for unapproved uses, including lupus, the FDA says the latest instance is the first reported in a patient taking the drug for arthritis.

“The patient had a number of confounding factors that make it difficult to assess the potential role, if any, that Rituxan exposure may have played,” a Genentech spokeswoman tells the Associated Press, adding that the biotech disclosed the death during its July earnings call and the labeling mentions the infection risk.

According to the FDA’s web site, the patient was undergoing chemotherapy and radiation treatment for cancer in the months before she developed the infection, known as progressive multifocal leukoencephalopathy, or PML. The agency noted there are no known treatments for PML.

Genentech sent a letter to doctors about the case earlier this month. Rituxan is Genentech’s second-best selling drug with $2.3 billion in sales last year, just behind the Avastin cancer treatment. This is the second disappointment associated with the drug this year. A few months ago, a trial showed Rituxan failed as a treatment for lupus (read here).

Reports of PML with Biogen Idec’s multiple sclerosis drug Tysabri have weighed on company shares in recent months. In July, the company reported two new cases of the disease in European patients. The drug was pulled from the market in 2005 after being linked to the rare brain disease but was reintroduced under restricted sales conditions in mid-2006.

Source: Associated Press