Elan and Biogen Idec said today that a Phase III trial of their multiple sclerosis drug Tysabri showed significant effects on patient quality of life.

Earlier, the two companies said data from the Phase III trial had shown Tysabri (natalizumab) provided significant improvements in disability progression, relapse rate and lesion formation, as measured by magnetic resonance imaging.

Richard Rudick, of the Cleveland Clinic, who presented the findings at the AAN meeting, said: 'We have never before observed positive findings on our quality of life measures in a Phase III MS study."

The data, presented at the American Academy of Neurology meeting in San Diego, bode well for the prospects of the drug, which looks set to return to market after being withdrawn from sale in February 2005 after being linked to a rare brain disease called progressive multifocal leukoencephalopathy.

A US Food and Drug Administration (FDA) advisory committee recommended the re-introduction of Tysabri as a treatment for relapsing forms of MS in March, prompting Elan and Biogen to re-start clinical testing of the drug. The two companies have said they expect a decision from the FDA before June 28 this year.

Analysts said the new data reinforced the clinical profile of Tysabri, and could eventually lead to labelling that would indicate superiority in efficacy to currently-marketed MS drugs, including the beta interferons.