Tysabri was voluntarily withdrawn from the multiple sclerosis market in February 2005 following two cases of multifocal leukoencephalopathy (PML) resulting in fatality. However, recently published data indicates that PML is only linked to patients also taking Avonex or recent immunosuppressive therapy. Datamonitor expects that Tysabri will be relaunched as a monotherapy in late 2005/early 2006.

• Overview of Tysabri's product history from development to approval and launch, and subsequent withdrawal from the market
• Viewpoints from key opinion leaders on the withdrawal and potential relaunch of Tysabri
• Biogen-Idec and Elan's options and potential strategies for the relaunch of Tysabri
• Assessment of the future product positioning and life-cycle management strategies open to Tysabri

Strong evidence suggests that Tysabri used in conjunction with Avonex, increases the concentration of Tysabri in the body, while also decreasing the clearance rate of the drug, resulting in immune suppression. In contrast, the concentration and clearance of Tysabri when used in monotherapy remains within acceptable, safe levels.

At present, the future for Tysabri is still uncertain, although Datamonitor forecasts that Tysabri will be relaunched as a monotherapy in the US in late 2005 or early 2006, with a subsequent launch in EU countries.

Datamonitor expects that Tysabri's labeling will certainly feature a black box warning against the use of the drug in combination with Avonex and will also give strong warnings against the use of Tysabri in conjunction with all beta interferons, and the use of medication in immunosuppressed patients.

• Assess the future commercial viability of Tysabri, based on clinical trial data and Datamonitor event analysis
• Gain valuable insight into the views of key opinion leaders regarding the Tysabri withdrawal, perceived safety, and potential future usage
• Benchmark Tysabri against current and future multiple sclerosis therapies