Elan and Biogen Idec have returned their multiple sclerosis drug Tysabri to the market in the USA and several European countries as a monotherapy for the disease.

The US Food and Drug Administration and European Medicines Agency both cleared Tysabri (natalizumab) to return last month with certain restrictions, after it was taken off the market in 2005 on safety concerns.

Elan and Biogen Idec have developed a risk-management plan to give early warning if cases of the rare but potentially fatal disease progressive multifocal leukoencephalopathy (PML), which was seen in three patients taking Tysabri, occur again. This means that only doctors who have gone through a training and registration programme will be able to prescribe the drug.

To keep the supply chain well-controlled, Elan and Biogen Idec have appointed a network of designated distribution companies and specialty pharmacies to handle Tysabri. The drug has been returned to market with premium pricing, 20% more than when it was first available, now costing $28,400 per patient per year.

Biogen Idec and Elan are carrying out a major, open-label study of Tysabri to try to generate long-term safety data and rebuild confidence in the drug's safety.