The US Food and Drug Administration has issued a safety warning about Genzyme and Schering AG’s Campath (alemtuzumab) in patients with multiple sclerosis, more than two months after a patient died after taking the drug in a clinical trial.

The warning is thought to be intended to discourage doctors from prescribing the drug off-label for MS patients. Campath is approved for the treatment of a form of blood cancer called B-cell chronic lymphocytic leukaemia. The label for the drug already carries a warning about serious and rare blood problems that may happen with its use.

In September, Genzyme and Schering called a halt to a clinical trial of Campath in MS, after three cases of severe idiopathic thrombocytopenic purpura (ITP) were seen in patients taking the drug. One of the patients died.

But the high level of efficacy seen in the study prompted the companies to suggest that Campath should not be abandoned as an MS treatment. Rather, they suggested that protocols should be designed to allow patients to be treated with the drug in trials whilst minimizing the risk of ITP developing.

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.