Two men in intensive care after taking part in a clinical trial remain critically ill and are unlikely to make any early improvement, their doctor said yesterday.
Six men were taken ill during the trial in London to test a drug designed to treat chronic inflammatory conditions and leukaemia.
Four are in serious condition but have shown signs of improvement.
"The two men remain critical and it could be a while until they show significant change," said Northwick Park Hospital's Clinical Director of Intensive Care, Ganesh Suntharalingham.
"The four who are seriously unwell are continuing to show signs of improvement but it is still early days," he added.
"We are still treating their inflammatory response following the drug trial ... and are providing full supportive care for the organs affected by this process."
Relatives and friends of the two men have said the volunteers' features have become severely swollen.
The hospital said patients in intensive care often needed a lot of fluid which could result in severe swelling and said this could reduce as they recover.
Suntharalingham said the six men could make a full recovery but added it was too early to make predictions. He said he did now know what had caused the violent reaction.
The trial was being run by US drug research company Parexel International on behalf of German pharmaceutical company TeGenero AG.
They were testing a new biotech drug known as TGN 1412.
Thomas Hanke, chief scientific officer of the German firm, said the new medicine had shown no safety problems in laboratory trials.
He said they were "shocked" by the developments and, asked by reporters if the company had apologised, he replied "yes."
Parexel said it had operated within regulatory guidelines.
Yesterday, one of two men given a harmless placebo, told Sky News how he had watched in horror as the six around him collapsed.
Raste Khan said the volunteers were writhing in agony, continually vomiting and screaming about the pain in their heads.
He said they became ill minutes after taking the drug.
"This one man was yelling 'doctor, my head hurts, my back hurts. I need help, I can't breathe.' He was just shouting and rambling to himself," he said.
"It was like Russian Roulette - two of us got away and were lucky."
A girlfriend of another volunteer said they had been told to pray for a miracle.
Myfanwy Marshal told reporters how her boyfriend looked like the "Elephant Man" - a freak show figure in Victorian Britain whose head ballooned until his skull was wider than his waist.
All his internal organs had failed, she added.
Britain's Medicines and Healthcare products Regulatory Agency have said they are working with police and the Department of Health to investigate what went wrong.
PHOTO CAPTION
Intensive care unit consultant Ganesh Suntharalingam makes a statement at Northwick Park Hospital, London, Thursday, March 16, 2006. (AP)