Ireland’s Elan Corp and its US partner Biogen Idec have released more favourable sales and safety data on their multiple sclerosis drug Tysabri.

The firms said that as of late December, more than 21,000 patients were on Tysabri (natalizumab) and to date, the safety data “continue to support a favourable benefit-risk profile”. Specifically, in the USA, approximately 12,900 patients were on the drug on a commercial basis and 2,500 physicians have prescribed the therapy. Most interestingly, Elan and Biogen added that there have been no cases of progressive multifocal leukoencephalopathy, a rare brain disease, since the re-launch of Tysabri in July 2006.

The drug was pulled off the market on safety concerns in February 2005, and its reintroduction came with restrictions to monitor patients for symptoms of PML. Tysabri is key to the fortunes of both firms (but especially Elan) and a joint meeting of the US Food and Drug Administration’s Gastrointestinal Drugs Drug Safety and Risk Management Advisory Committee voted 12 to three back in August to support the treatment in Crohn’s disease.

However, European regulators have looked less favourably on the Crohn’s indication and adopted a negative opinion on the marketing authorisation filing in November.