There were celebrations on both sides of the Atlantic yesterday after a US Food and Drug Administration (FDA) advisory committee recommended that Biogen Idec and Elan’s multiple sclerosis drug Tysabri should be returned to the market.

Tysabri was taken off the market in February 2005, just four months after it reached the market, after it emerged that three patients taking the drug developed a rare brain disease called progressive multifocal leukoencephalopathy, leading to two deaths.

The panel voted unanimously that Tysabri (natalizumab) should be reintroduced for the treatment of patients with the relapsing-remitting form of MS. A second vote on whether the drug should be used as a first-line therapy in MS patients passed by a narrower (7 to 5) margin, according to

Helping Elan and Biogen Idec’s case was new data reported in the New England Journal of Medicine last week, which backed the efficacy of Tysabri and uncovered no new cases of PML.

The FDA does not have to follow its advice, and much will depend on discussions surrounding a risk-management plan for patients receiving the drug, including a mandatory registry of recipients. The problem for the agency is that PML is often irreversible and there is no known treatment, so patients must be made fully aware of the risks before starting treatment with Tysabri, according to the agency.

Given the concerns, Biogen Idec and Elan have suggested limiting the use of Tysabri to include only patents with relapsing MS. The panel also said the drug should not be used in combination with other MS drugs, such as Biogen Idec’s own Avonex (interferon beta-1a), Serono’s Rebif (interferon beta-1a), Berlex/Chiron’s Betaseron interferon beta-1b) or Teva’s Copaxone (glatiramer acetate).

All cases of PML occurred in patients taking the drug alongside Avonex, although the committee said there was no indication that the side effect could not occur with Tysabri monotherapy.

The agency is due to deliver a verdict by March 29.

Jennifer Chao, an analyst at Deutsche Bank, said Tysabri could achieve sales of $125 million this year and $325 million in 2007 if the FDA comes down in favour of its return.