The US Food and Drug Administration (FDA) is investigating the potential link between Novartis' multiple sclerosis (MS) drug Gilenya and a rare brain infection.
The investigation was launched after a patient treated with Gilenya (fingolimod) in Europe developed progressive multifocal leukoencephalopathy (PML) - an infection that has been associated with fellow MS drug Tysabri (natalizumab), which is marketed by Biogen Idec.
Gilenya has already been linked to PML following a report last year that an MS patient taking the drug had developed the infection, although that patient had already received Tysabri earlier in their treatment making it difficult to determine if Gilenya played a part in the development of PML.
However, this latest case is the first time a patient on Gilenya has developed PML without also receiving Tysabri at some point in their treatment, and the FDA is now working with Novartis to determine if the drug was the cause.
Gilenya was launched with much fanfare in 2010 as the first oral drug for relapsing forms of MS and has gone on to become one of Novartis' key products, gaining blockbuster status in 2012 with sales of $1.2bn.
Any relationship with PML would be a blow for Novartis' plans for Gilenya, although the company can take heart from Biogen Idec's experience with Tysabri, which was withdrawn in 2005 after being linked to PML, but reintroduced in 2006 after physicians using the drug developed a greater understanding about the risk factors for developing the condition.