The Food and Drug Administration in the U.S. has given it's approval for the multiple sclerosis drug Tysabri to be put back on the market.
Tysabri was given FDA approval in November 2004 and withdrawn from the market in February 2005 following the revelation that three patients taking the drug developed a rare but potentially fatal brain disease, progressive multifocal leukoencephalopathy (PML); two consequently died.
The drug which is manufactured by Biogen has been allowed back on the market with certain restrictions.
Doctors, infusion centers and pharmacies must now register with the companies before prescribing Tysabri and patients must also enroll before beginning treatment and are required to have a magnetic resonance imaging scan (MRI) before treatment starts in order to distinguish MS symptoms from those linked to the brain disease.
Patients also will have to undergo evaluations three and six months after they start taking the drug, and then every six months after.
The drug is administered once-a-month by an intravenously and is aimed at treating those patients with relapsing MS, to reduce the frequency of flare-ups, which affect sight and mobility.
The FDA also recommends that Tysabri should be used as a stand-alone treatment and not combined with other drugs which suppress the immune system.
Previously, some doctors prescribed it with Avonex.
The agency also advises that the drug should only be used in patients who have not responded adequately to, or cannot tolerate, other MS treatments.
According to National Institutes of Health figures between 250,000 to 350,000 Americans have been diagnosed with MS, a disease of the central nervous system for which there is no cure.
The degenerative disease attacks the nerve tissue by way of the immune system, initially causing blurred vision and leading to muscle weakness and memory problems, among other symptoms.
Recent studies found that Tysabri alone or with standard interferon treatment cut the rate of relapse in MS patients by as much as two-thirds after two years and reduced the number of people whose MS got worse.
The drug works by blocking the destructive immune cells leaving the bloodstream and entering the brain, where they can inflame and damage nerves.
Researchers estimate that one in every 1,000 Tysabri users risk contracting the JC virus that causes PML.
The majority of MS patients support the return of Tysabri regardless of the risks.
According to the FDA, Tysabri's other side effects include allergic reactions and an increased risk of unusual or serious infections.
Tysabri could be back on the market by July.
Before the deaths last year Tysabri had been expected to be a highly successful product with a potential billion-dollar-a-year profit.
Tysabri is produced by Biogen Idec and distributed by Elan Corp.