Elan and Biogen have been given a green light from the US Food and Drug Administration to update the product labelling for their multiple sclerosis drug Tysabri (natalizumab) to help identify those at most risk of developing the rare but potentially fatal viral brain infection PML (progressive multifocal leukoencephalopathy). 

The labelling now suggests patients should be tested to see whether or not they have previously been exposed to the JC virus – prior infection and a corresponding anti-JCV antibody positive status means a multiple sclerosis patient runs a greater risk of developing PML, particularly if they have also received immunosuppressant therapy and have been on Tysabri for more than two years.

In analyses, patients who were anti-JCV antibody positive had a greater chance of developing PML to varying degrees depending on prior IS use and duration of Tysabri treatment. Irrespective of treatment, around 55% of MS patients are anti-JCV positive, the companies note.

These attempts to personalise medicines means that a product that a few years ago might have been taken off the market because of the small but possible risk of PML, can now be used effectively in a targeted group of patients. “Our development of the risk stratification algorithm and subsequent efforts to support the commercial availability of anti-JCV antibody testing reflect our commitment to providing patients and their physicians with additional guidance to help them make more personalised treatment decisions,” notes George Scangos, chief executive of Biogen.

Tysabri is one of the key drivers of growth at Biogen, bringing $277.3 million into its coffers, up 26%, in the third quarter of last year. Overall its profits were up 38% to $351.8 million for the period. 

Stratify JCV Antibody ELISA testing, developed by Quest Diagnotics, is the first blood test to be approved by the FDA to detect antibodies to the JC virus.