The odds on Biogen Idec and Elan getting a positive response from US regulators in their bid to get their multiple sclerosis drug Tysabri approved for Crohn’s disease have lengthened after a less-than-glowing report.

The report, issued by staff members at the US Food and Drug Administration ahead of an agency panel meeting on Tuesday, states that clinical studies of Tysabri (natalizumab) show that its effectiveness as a treatment for Crohn’s disease is not "clearly distinguished" from current therapies. It goes on to claim that “the benefit and risk considerations in the Crohn's disease population are considerably different from those in the multiple sclerosis population".

The FDA advisory panel's meeting comes less than two weeks after the European Medicines Agency’s Committee for Medicinal Products for Human Use declined to recommend Tysabri, saying there was "insufficient evidence" that it was effective in treating Crohn's disease. Biogen and Elan are appealing the decision by the CHMP which also voiced concerns over potentially serious side effects linked to the drug, including progressive multifocal leukoencephalopathy, a brain infection that has played a major part in the life of Tysabri to date.

It was approved in the USA in November 2004, then pulled from the market just a few months after a patient died from PML while taking Tysabri. It remerged last summer after receiving clearance, with certain restrictions, from regulators in the USA and Europe.

Elan losses widen

Tysabri is a key drug particularly for Ireland’s Elan which has just posted a second quarter loss of $141.1 million, or $0.30 per share, up from $90.5 million, or $0.21 for the corresponding period last year. The increase was mainly due to a non-cash charge of $52.2 million related to the write-down of the company’s Maxipime (cefepime) antibiotic following the earlier-than-expected arrival of a generic competitor.

Tysabri had what Elan’s chief financial officer Shane Cooke described as “a solid quarter” with approximately 14,000 patients on therapy as of mid-July 2007, “an increase of over 40% from when we reported last quarter”. Out of total revenues of $188.5 million (+38.1%), Tysabri brought in $46.9 million.