The two firms said a Food and Drug Administration (FDA) advisory committee will review the drug on 31 July. If the outcome of the review is positive, the future could look bright again for Tysabri, which has suffered a number of setbacks since its launch three years ago. Tysabri (natalizumab) was approved by the FDA in November 2004 for use in patients with relapsing forms of MS. However, the drug was withdrawn from the market three months later after reports of three trial volunteers developing progressive multifocal leukoencephalopathy (PML), a progressive and frequently fatal condition. A subsequent safety review of the drug was completed in March 2006 and found no new cases of PML among more than 2,000 patients treated for MS in clinical trials and in commercial use. As a result, the FDA resumed prescribing of the drug in June last year under specific requirements: patients must take part in a risk-minimisation programme with mandatory patient registration and regular follow-up to identify PML cases as soon as they occurred. However, Tysabri recently suffered another blow when NICE, the UK government's drug watchdog, recommended against the prescription of Tysabri. Based on data from clinical trials and the cost of the drug, NICE advised that the efficacy of Tysabri is not proven and that the cost is simply too much, sparking a strong reaction from the MS Society, which responded saying it was appalled by the watchdog's decision. To make things worse, recent research from Decision Resources suggested that the chequered past of Tysabri could have impaired its once-promising market potential. Before and immediately after its approval, analysts had forecast annual sales of between $2bn (€1.4bn) and more than $3bn. However, as a result of its withdrawal and late re-launch in the third quarter of 2006, global sales of Tysabri were only $74m last year - a revenue shared 50/50 between the two firms. Moreover, a recent report from Datamonitor suggests that the future of Tysabri is threatened by a breed of newly formulated MS treatments ready to conquer the market. According to the research, there is a significant need for a MS drug with superior efficacy to current therapies with a less invasive and time-consuming route of administration. Novartis' oral Fingolimod (FTY720) is tipped to represent the most highly anticipated pipeline drug since the initial launch of Tysabri. Getting the drug approved for a new indication such as Crohn's disease - which affects around one million people worldwide - could therefore give Tysabri a boost in terms of sales. Tysabri is a humanised monoclonal antibody (mAb) alpha-4 antagonist indicated as a single disease modifying therapy in highly active relapsing remitting MS for patients with high disease activity despite treatment with a beta-interferon or in patients with rapidly evolving severe relapsing remitting MS. Massachusetts-based Biogen Idec and Irish company Elan said about 10,000 sufferers of MS were using Tysabri today and about 300 were signing up each week to start taking the drug.