California-based biotech Genentech Inc announced the revised label and product information for its drug Rituxan – approved for non-Hodgkin´s lymphoma and rheumatoid arthritis – after a patient prescribed this medication died from progressive multifocal leukoencephalopathy (PML) 18 months after starting treatment.

Rituxan (generically rituximab, and also called MabThera in other countries) is jointly marketed by Genentech and Biogen Idec - its original developer - in the U.S., and with Roche Holdings in Europe.

Rituxan/MabThera already carried a warning of the PML risk, and in light of this fatal case, Genentech and the FDA are advising doctors to watch for any neurological signs of PML in patients taking Rituxan, as there is no cure for this disorder.

Rituxan is the second drug on the market linked to this usually fatal brain disease – the other is Tysabri, also developed by Biogen, and jointly marketed with Ireland´s Elan Corp for patients with multiple sclerosis. Both drugs are built on antibodies that manipulate the immune system.

Tysabri (natalizumab) was removed from the market in 2005 after several fatal PML cases, but has since returned under strict control. However, there have been other PML cases in multiple sclerosis patients since it was reintroduced on the market in 2006.

Rituxan/MabThera had sales of over $ 2.7 billion dollars in the first six months of this year, the fourth-placed best selling drug worldwide.