Biogen Idec and Elan Corp have received a pleasant surprise with the news that a US advisory panel recommended that the firms’ multiple sclerosis drug Tysabri can also be used to treat Crohn's disease.

Elan noted that a joint meeting of the US Food and Drug Administration’s Gastrointestinal Drugs Drug Safety and Risk Management Advisory Committee voted 12 to three, with two abstaining, to recommend approval of Tysabri (natalizumab) as a treatment for moderate-to-severe Crohn's disease in patients who have failed or cannot tolerate available therapies.

The agency is not bound by the recommendation but normally goes along with its advisors and full approval now seems likely given that Elan and Biogen said they will continue to work closely with the FDA to adapt the existing Tysabri risk management plan and address any other issues raised by the committees on this new indication.

The news came as somewhat of a surprise, given that prior to the meeting, a report issued by agency staff members stated that clinical studies of Tysabri show that its effectiveness as a treatment for Crohn’s disease is not "clearly distinguished" from current therapies. It went 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 advisory panel's decision is doubly surprising as it comes 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 that decision 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.

Still the FDA panelists are backing the drug for Crohn’s disease but on the condition that the companies implement a plan "with very strict post-marketing surveillance".