FDA sees continued risk with Tysabri for Crohnís disease

The FDA has upheld its concerns over Biogen Idecís and Elanís Tysabri (natalizumab) for use in the treatment of Crohnís disease because of possible fatal side effects.

The FDA has said that patients taking Tysabri for Crohnís disease, an inflammatory disorder of the alimentary canal, could develop a rare and untreatable CNS disease which is usually fatal after six months.

The FDA posted its review of the drug ahead of a meeting where outside experts will vote on whether the drug should be approved. The government is not required to follow the experts' advice, though in practice this usually happens.

As a result of the FDA announcement, US-based Biogenís shares dropped USD 0.86 (1.5 per cent) on 27 July to rest at USD 57.33 in morning trading. Ireland-headquartered Elanís shares fell USD 0.59 cents (three per cent) to USD 19.14.

Tysabri was temporarily taken off the US MS market in February 2005 when three patients developed the rare nervous system disorder known as multifocal leukoencephalopathy (PML).

The FDA eventually decided to put the drug back on the market in 2006, under the condition that patients use it alone, and not in combination with drugs used to suppress the immune system. The FDA determined that combining Tysabri with these treatments could increase risk of PML.

In its Crohnís review of Tysabri, FDA said it would be more difficult to assure the safety of the drug in such patients, as they are more likely to take immune-system suppressing drugs as an adjunctive therapy. The agency added that Biogen had not conducted several safety analyses which had been previously requested.

Despite these concerns, the FDA has said that the drug seems to be effective in preventing inflammation of the intestine wall in Crohn's disease patients.

If approved, Tysabri for Crohnís could add USD 300m in sales to its existing income, according to Bear Stearns analysts. The drug would then compete with J&Jís Remicade (infliximab), which is currently the top-selling Crohn's treatment.

Tysabri is already competing with Tevaís established MS therapy, Copaxone (glatiramer acetate). In FY06, in-market global sales of Copaxone reached USD 1.4bn, an increase of 20 per cent on FY05 figures. Sales of Copaxone in the EU increased 26 per cent to reach USD 498m, driven by significant sales increases in the UK, France and Germany, which are the largest MS markets in the EU.