The labeling for cancer and rheumatoid arthritis drug Rituxan is being revised after the US Food and Drug Administration said on Thursday a woman died of the brain infection progressive multifocal leukoencephalopathy (PML).

Progressive multifocal leucoencephalopathy is a slow virus infection that usually occurs in patients with impaired cell-mediated immunity. It is a disease of the white matter of the brain. The first symptoms of PML are weakness or coordination problems in an arm or leg. There may be difficulty thinking or speaking. Vision and memory problems, seizures, and headaches can occur.

Rituxan, known generically as rituximab and manufactured by Genentech and Biogen Idec., was approved to treat non-Hodgkin’s lymphoma in 1997 and rheumatoid arthritis in 2006 and had sales last year of $2.3 billion in the U.S. alone.

According to the FDA, this is the first report of the infection in an individual undergoing treatment for arthritis. Cases of PML have previously been reported in patients taking Rituxan for unapproved uses. 

The woman developed the infection more than a year and a half after discontinuing treatment with Rituxan, the FDA said. Also, the woman had also received chemotherapy agents about nine months earlier.

Tara Cooper, a representative for Genentech underlined that the risk of developing PML is already mentioned on Rituxan’s label.

“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,” Cooper said.

However, the FDA urged doctors treating rheumatoid arthritis to look for neurological problems in patients taking Rituxan.