Six men are in intensive care after taking part in a clinical trial to treat leukaemia and inflammatory conditions. The trial was immediately suspended as the patients were admitted to Northwick Park Hospital in north London after reacting badly to the anti-inflammatory drug. Relatives were with the patients, who suffered multiple organ failure. Some cases are said to be life-threatening.

They became ill within hours of taking the drug. Parexel, the clinical research company running the trial, said it had operated within regulatory guidelines and that such adverse reactions to drugs were extremely rare.

The Medicines and Healthcare products Regulatory Agency has sent inspectors to the research unit on the hospital campus to investigate. They were working with the Metropolitan Police and the Department of Health.

A spokeswoman for Northwick Park Hospital said today that the six men remained in intensive care. Two of them are in a "critical condition'', she said, while the other four are "serious but stable''.