Clinical trials of Tysabri, the troubled multiple sclerosis treatment, are to begin again in the US after the FDA gave permission to proceed.

The regulator has allowed manufacturers Biogen-IDEC and Elan Corporation to restart trials of the drug a year on from its suspension in February 2005, after three patients developed progressive multifocal leukoencephalopathy (PML), a brain infection which is frequently fatal.

The drug had passed through phase III and had been launched onto the US market at the beginning of 2005, only to be pulled from the market within weeks after the death of two patients, and another who became critically ill.

Two patients were being treated with Tysabri (natalizumab) for MS, and one patient being treated for Crohn's Disease.

The drug had once been tipped to be a giant step forward in the treatment of MS, and was forecast to earn the marketing partners more than $1 billion in peak sales.

Now the drug returns to small scale safety trials, with MS patients resuming treatment after talking to their doctors about the potential risks and potential benefits of the drug.

The FDA said that although the drug had shown benefit in patients with relapsing-remitting MS, it stressed that concern about PML remained.

The companies are working with the FDA to uncover any undiagnosed early stage PML, discover what factors might have contributed to the three known PML cases, and to look at what could be done to minimise risk in the future.

An FDA committee will meet on 7 March to consider its future, including a possible return to the market and a risk management plan.

Related articles:

Wyeth joins search for promising TLR drugs 

Wednesday, February 15, 2006

pharmafocus@wiley.co.uk