What is PML?

THE Irish pharmaceutical company Elan yesterday refused to withdraw its drug Tysabri from the market, saying its side effects are worth the risk.

The chief executive of the company, Kelly Martin, insisted it was a safe drug and hinted stock markets had overreacted to fresh reports of users developing a deadly brain disease from taking it.

Shares in the company plunged almost 60% on the Irish Stock Exchange yesterday after two new cases of progressive multifocal leukoencephalopathy (PML) were identified arising from the use of the drug to treat multiple sclerosis.