Tysabri, which is used in the treatment of Multiple Sclerosis (MS), has been withdrawn from market after the two patients taking the drug complained of neurological disorders. The relationship between the drug and Progressive Multifocal Leukoencephalopathy (PML) is being researched by the scientists. If the drug is deemed to pose a significant risk, it could be a serious setback for the entire class of drugs, which work by blocking passage of immune cells in to the brain.
"Other cell migration inhibitors in development will have to be carefully tested, says Howard Weiner, director of the partners MS center at Brigham and Women's Hospital. Several companies are developing drugs that use the same compounds to treat Crohn disease, rheumatoid arthritis and asthma. The US FDA has halted a phase 2 trial of a GlaxoSmithKline drug that targets the same protein, alpha-4 integrin, as Tysabri. Australian biotech Antisense Therapuetics stopped Phase 2 trial in March for similar MS drugs, which the company had also planned to develop as an asthma treatment. The FDA in November 2004 granted Tysabri fast track approval, after initial phase 3 results attacks by as much as 66%. Tysabri was expected to be a major blockbuster for its manufacturer Biogen Idec, but the company suspended sales of Tysabri in February, after learning of the two PML cases, one of which was fatal. The company also halted trials of the drug for rheumatoid arthritis and Crohn disease.
There has never previously been a documented case of PML in MS patients, even though these patients have been treated with many types of immunosuppresants. Both patients diagnosed with PML had taken Tysabri with Avonex, another MS drug, for two years n clinical trials.
Source: Nature Medicine