Elan and Biogen Idec say they have now completed their safety investigation into Tysabri (natalizumab) and found no further evidence of the serious side effect that led the multiple sclerosis drug to be withdrawn from the market earlier this year.

Tysabri was voluntarily pulled from sale after three cases of a serious brain disease known as progressive multifocal leukoencephalopathy (PML), two of which were fatal, were found in patients taking the drug for MS [[01/03/05a]]. The news hit both companies hard, as Tysabri was considered a key prospect for their growth and had been tipped to achieve peak sales of $2 to $3 billion dollars by 2007 [[09/09/05d]].

Elan and Biogen Idec have since undertaken a comprehensive safety investigation into all patients who have received the drug, which is also in development as a treatment for rheumatoid arthritis and Crohn’s disease. The companies previously reported that its investigation of MS patients taking Tysabri using neurological exams and magnetic resonance imaging had found no additional cases of PML. Now, the same result has been achieved in a review of all patients who received the drug in trials for RA and Crohn’s disease.

“The Tysabri safety evaluation is now complete,” said Elan and Biogen Idec in a statement. This is good news for the future prospects of the drug: the two companies filed for approval to place Tysabri back on the US market last month, and have also submitted additional data to the European Medicines Agency (EMEA), which had not approved the drug before it was withdrawn in the USA [[27/09/05a]].

More than 1,500 Crohn’s and RA patients from clinical trials were eligible for the safety evaluation, and 88% of them patients took part in the study.