The US Food and Drug Administration has ruled that US drugmaker Biogen Idec and Ireland-based Elan can resume clinical trials of their embattled multiple sclerosis therapy Tysabri (natalizumab), in a move that could signal the first step towards a return to market for the drug.

Although the FDA is not due to decide whether to give the full go-ahead until early next month, this latest development, which allows only patients taking part in safety studies before sales of Tysabri were halted to resume treatment, does seem to indicate that the agency is leaning towards a green light for the agent to return to market.

Biogen and Elan were forced to take Tysabri off the shelves in February last year, after it emerged that three patients taking the drug developed a rare brain disease called progressive multifocal leukoencephalopathy, leading to two deaths.

The news came as a severe blow to both firms, which were pinning their hopes on Tysabri for future growth, given that it had been tipped to achieve peak sales of $2 to $3 billion by 2007. But the firms' comprehensive safety study, which they completed in October last year, revealed no further incidences of PML, sparking hopes of an eventual return to market.

Meanwhile, in other good news for Biogen, the group saw its fourth-quarter 2005 profit skyrocket 94% to $55.6 million, or $0.16 a share, beating Wall Street expectations on strong sales. Excluding special items, the company generated a profit of $165 million, or $0.48 per share.

Total revenues rose 8% to $632.9 million, bolstered by sales of the group’s older multiple sclerosis treatment, Avonex (interferon beta-1a), which grew 12% to $413 million, and Rituxan (rituximab), for the treatment of lymphoma, up 6% at $182 million.

For this year, Biogen has predicted earnings per share of $1.95 to $2.10, with around $0.06-$0.09 a share for option expensing, and capital spending of $190 million to $275 million.

The news was received positively by investors; Biogen’s Nasdaq-traded shares closed up 3% at $45.72, while Elan stock climbed 3.1% to close at $14.54 after a bout of frenzied trading on the New York Stock Exchange.