Shares in pharmaceutical  company Elan surged in Dublin today after it released figures showing that its suspended Tysabri drug improved the effectiveness of Biogen's Avonex in the treatment of multiple sclerosis.

'The addition of Tysabri to Avonex resulted in a 24% reduction in the risk of disability progression compared to the effect provided by Avonex alone,' the two companies said. There was also a 56% relative reduction in the rate of clinical relapses.

The companies halted sales of and trials of Tysabri in late February after it was discovered that some patients taking the drug in combination with another treatment had contracted a rare brain disease called PML.

The two firms are currently conducting a safety review before a decision can be made on a possible return of Tysabri to the market. Elan reports its second quarter results on July 28, and may give an update on the progress of the review then.

Shares in Elan closed 56 cent higher at €6.57 in Dublin this evening.