Elan’s multiple sclerosis drug Tysabri received a boost yesterday when European regulators approved updated labelling.

The addition of a warning citing a further risk factor, anti-JC virus antibody status, is seen as allowing doctors to assess more accurately patients for suitability for treatment with the drug. A test to determine whether a patient has the JC virus has been developed by Elan and its US partner Biogen, and is expected to be commercially available in the US market by the middle of the year, according to a spokeswoman for the Irish company. It is currently being used in trials.

The major concern about Tysabri has been the onset of a potentially fatal brain condition, progressive multifocal leukoencephalopathy. However, all incidences of the disease have occurred in people with the JC virus, who account for just over half the MS population. Patients testing negative for JCV are therefore seen as being able to take the drug.

Elan will report figures for its fiscal first quarter tomorrow.