ELAN is looking for approval to sell the drug Tysabri to more multiple sclerosis sufferers.
The move could boost sales of the drug, which is a highly effective treatment for some of those who have one of the commonest medical problems in the western world.
Demand for Tysabri has been muted because it can trigger a potentially fatal viral infection known as progressive multi-focal leukoencephalopathy, or PML, in some patients.
Dublin-based Elan and US partner Biogen now say that more people can use the drug thanks to a new test for the virus, which can predict whether patients are at risk of developing PML.
Elan and Biogen said yesterday that they had submitted applications to the US Food and Drug Administration and the European Medicines Agency seeking approval for a new label which allows Tysabri to be used by patients with relapsing forms of multiple sclerosis who have tested negative for antibodies to the virus which triggers problems for Tysabri users.
Davy Stockbrokers analyst Jack Gorman welcomed the move. "Elan and BIIB have been building a significant body of evidence in recent years to establish the major risk factors," he said.
"Formalising a label update is a natural next step in these initiatives and would be supportive of our thesis that further strong patient growth can be achieved for Tysabri in the coming years."
Davy said it expected more than 92,000 patients to use Tysabri within three years or more than 30pc more than current levels.