The US Food and Drug Administration (FDA) has placed a safety notice in relation to Elan’s multiple sclerosis drug Tysabri on its website.

The risk of a potentially fatal brain disorder with Tysabri increases as patients receive more infusions, the FDA says.

A spokeswoman for Biogen, Elan’s marketing partner for Tysabri, said labels on the drug had been updated to take account of the higher risk of long-term usage as of November 2009.

The warning is based on the 31 confirmed cases of progressive multifocal leukoencephalopathy (PML), a brain infection that can be fatal.