An interim report from Britain's medicines watchdog today said there was no obvious explanation for what went wrong during a catastrophic drug trial which left six volunteers near death.

Six healthy young men suffered organ failure and violent, life-threatening side-effects after being injected with the anti-inflammatory drug TGN1412 during a clinical trial in north-west London on March 13.

One volunteer injected with a placebo instead of the real drug described how he watched his fellow volunteers at Northwick Park Hospital screaming and vomiting and passing out within minutes of the injections.

The men, who were paid £2,000 to take part in the trial, were taken from the small private research unit to the intensive care department of the adjoining NHS hospital, and placed on life support.

The drug was developed by TeGenero, a small German research company, as a possible treatment for rheumatoid arthritis, leukaemia and multiple sclerosis.

After laboratory analyses and tests on animals, TGN1412 was cleared for its first trials on humans, which were carried out by Parexel, a medical research company. The human volunteers were given doses 500 times lower than those given to monkeys.

Today the Medicines and Healthcare Products Regulatory Agency said that its investigation into the incident had found no evidence that there was any problem with the way the drug was manufactured or administered.

"There’s no simple explanation of what happened," said Professor Kent Woods, the chief executive of the MHRA, which regulates 350 Phase 1 clinical trials -- the first testing on humans -- in the UK every year.

In a statement, Professor Woods added that the drug did not appear to have been contaminated "or to have contained anything other than the correct ingredients".

"Neither have we found anything in the way the trial was run which contributed to the adverse reactions experienced by the volunteers – it was run according to the agreed protocol, and the correct dose of the product was given to the patients."

The MHRA said that its findings were not conclusive and there was more investigation still to be done. "There are still further tests planned and until these are complete we cannot be firm about our conclusions. However, if these findings were to be confirmed, it would indicate that this product showed a pharmacological effect in man which was not seen in pre-clinical tests in animals at much higher doses.

"The Secretary of State for Health has therefore agreed to establish a group of leading international experts in the field to examine the issue further. The group will need to review the evidence from the TGN1412 case and consider what necessary changes to clinical trials may be required."

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