Parexel International, a Boston company that ran the test facility in London’s Northwick Park Hospital, said the trial followed all medical norms and that the reactions were totally unforeseen.
“This type of reaction is extremely rare, and is a very unusual event,” head of clinical pharmacology Herman Scholtz said in a Parexel statement.
Meanwhile the German manufacturer of the drug, TeGenero AG, also said the trial had conformed to best practices.
Two critically ill
All six men were still in the intensive care unit at Northwick Park Hospital in northwest London Thursday.
Shortly after being given a dose of the medicine, identified by TeGenero as TGN1412, the men started fainting, vomiting and writhing around in intense pain.
The volunteer drug testers, paid by Parexel, reportedly suffered inflammation which eventually affected their internal organs.
Two of the patients, reported to be horrifically bloated, remained critically ill, while the four others were seriously ill but showing signs of improvement, doctors said.
TGN1412 has been under development since 2000 to help treat immunological diseases such as multiple sclerosis, rheumatoid arthritis and certain cancers.
Eight men were involved in the clinical trial of a new drug but six were given actual doses with the other two given placebos.
Raste Khan, one of the men given a “dummy” dose, described the trial as a game of Russian roulette and how he now feels survivor’s guilt.
The 23-year-old student spoke to Sky News television and recounted a graphic scene inside the trial room.
One of the men he saw ill “was vomiting. He fainted on several occasions and then came back to consciousness, he was hyperventilating. He had pretty much all the nurses looking after him,” Mr Khan said.
“He looked like he was in the worst pain and then it kind of happened to everyone else,” he recalled.
“The gentleman on my right, was going through quite similar symptoms. He was quite a big person, he looked quite physically fit, and it took him a bit longer to kick in,” Mr Khan said.
“He was sweating, eventually he took his top off and sat on the edge of his bed, asked to use the toilet, he did several steps and collapsed, he just fainted,” Khan said.
Parexel paid the volunteers ₤2,300 (AU$5,481) to be test patients for TGN1412.
“I was doing it for the money. It’s not worth your life, nor, even if they survive, going through that,” he added.
Britain’s medicines watchdog halted the clinical trial on Wednesday and alerted its counterparts across the European Union as well as the US Food and Drug Administration.
Mr Scholtz said Parexel was working with the British watchdog, the Medicines
and Healthcare products Regulatory Agency (MHRA), to review all of the procedures that were followed.