Genzyme of the USA and Germany’s Schering AG have been forced to halt dosing in a Phase II trial of their cancer drug Campath (alemtuzumab) in patients with multiple sclerosis after a patient died of a serious bleeding disorder.

But the companies also reported that Campath, which is already approved to treat leukaemia, had shown excellent efficacy, cutting the relapse rate in patients with MS by 75% compared to the comparator drug, Serono’s blockbuster Rebif (interferon beta-1a). Campath is given just once a year, while Rebif is given three times a week.

However, with three cases of the bleeding disorder - idiopathic thrombocytopenic purpura (ITP) - seen in the first year of the three-year study, the investigators considered it prudent to suspend the trial and investigate the link. Overall, there were nine serious adverse reactions in the Campath group, compared to just three with Rebif.

Despite the side effects, Genzyme and Schering insisted the efficacy shown by Campath warranted its further development for MS. At present, the firms intend to start a Phase III trial of the drug in this indication in 2006, providing the side effect issue can be sorted out in cooperation with the US Food and Drug Administration and the clinical investigators. The hope is that ITP could be managed or prevented with supportive care, or that a lower dose of Campath might still confer a clinical benefit but reduce its toxicity.

Discussions are now ongoing to “ensure that a comprehensive approach is in place to manage patient safety,” said Genzyme and Schering in a statement. “Based on these results, we will be moving this program forward with a tremendous sense of urgency,” added Henri Termeer, chairman and chief executive of Genzyme.

Campath was approved in 2001 for B cell chronic lymphocytic leukaemia and is in Phase I development for non-Hodgkin’s lymphoma. Sales came in at around $77 million dollars last year.

MS is considered to be a promising use for the drug, because current therapies - namely the beta interferons and Teva’s Copaxone (glatiramer acetate) - have only modest efficacy in staving off damaging relapses. And the dearth of treatment options is felt more keenly than ever at present, as the much-touted new biologic for MS, Biogen Idec and Elan’s Tysabri (natalizumab), had to be pulled off the market earlier this year after it was linked to a rare but fatal brain disease [[01/03/05a]].