The FDA and Genentech have sent new warning letters to health care professionals about rituximab (Rituxan), a monoclonal antibody used in the treatment of a type of non-Hodgkin lymphoma (NHL). Two patients died after being treated with rituximab for systemic lupus erythematosus (SLE). The cause of death was a viral infection of the brain called progressive multifocal leukoencephalopathy (PML).

Rituximab is approved for the treatment of CD20-positive, B-cell NHL and for moderately to severely active rheumatoid arthritis when there has been inadequate response to other treatments, but it has also been prescribed off-label for other serious diseases and conditions, such as SLE. The FDA and Genentech, which manufactures rituximab, warned physicians to "maintain a high index of suspicion for the development of PML in patients under treatment with rituximab."

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