As regulators once again updated the label on Tysabri over the risk of a rare and potentially fatal brain disease, Biogen Idec and Elan Corp are planning a long-term trial that could lead to use of the multiple sclerosis blockbuster at the early stages of the condition.

Ian Hunter, an analyst at Irish broker Goodbody, notes that the trial, named Surpass, would measure the effectiveness of switching to Tysabri (natalizumab) for patients that have experienced disease breakthrough with either Teva Pharmaceutical Industries’ Copaxone (glatiramer acetate) or Merck KGaA's Rebif (interferon beta-1a). Recruitment for the study is planned to start this month and some 1,800 patients could participate.

The trial is part of Elan and Biogen’s bid to promote the use of Tysabri at the time of an initial disease breakthrough, rather than trying other medications beforehand. Although the two-year study is not expected to report results until 2013/2014, Mr Hunter says that it could, “if successful, provide a catalyst for Tysabri sales in what could be a more crowded MS drug market, particularly with the possible availability of oral drugs”.

News of the trial comes after the US Food and Drug Administration issued a safety announcement on Tysabri noting that the risk of developing progressive multifocal leukoencephalopathy increases with the number of infusions received.

This new safety information, based on reports of 31 confirmed cases of PML, will be included in the drug's label. Also added is information on the development of immune reconstitution inflammatory syndrome in patients who have developed PML and subsequently discontinued Tysabri. IRIS is a rare condition whereby patients can experience a severe inflammatory response to an infection and their symptoms can get worse, sometimes after a period of improvement.

The FDA also noted that in patients treated with 24 to 36 infusions, the overall worldwide rate and the rate in the USA of developing PML is similar to that seen during clinical trials (one case per 1,000 treated). Outside the USA. the rate is two cases per 1,000 patients but the FDA notes that the reasons for this difference are unknown and stresses that it continues to believe the benefits of Tysabri outweigh the risks.