Company treasurer John Conley told industry analysts, he believed Avonex would attract new users because of recently unveiled phase III clinical data indicating it can delay development of Ms in those with high risk of the disease.

Data from the so-called CHAMPS trial of 383 patients were released last month. They showed a "highly statistically significant" effect on delaying onset of clinically definite Ms in people who had already experienced damage to the fatty myelin tissue that surrounds and protects nerve fibers.Destruction of the myelin sheath can cause progressive paralysis that is a hallmark of the disease.

Conley said the data showed that Avonex reduced progression of Ms by 37 per cent and slowed the rate of brain shrinkage by 55 per cent, compared with those taking placebos in the approximately two year trial that was halted early because of the strongly favourable results.

Biogen plans this summer to ask US regulators to add the favourable data to the drug's package insert label, a move meant to spur increased usage by doctors and patients, Conley said at the PaineWebber Growth & Technology Conference in New York.