The report concluded that an unexpected biological effect was the most likely reason that all six men taking the monoclonal antibody TGN1412 during a recent Phase I trial suffered severe adverse reactions.
Parexel was hired to conduct the trial by German developer of the drug TeGenero and both companies, having since been the subject of an MHRA investigation, were cleared in the MHRA's final report released last week. Manufacturer of the drug Boehringer Ingelheim was also cleared.
"This is a very complex scientific issue, which will be reviewed by the independent expert scientific group appointed by the Secretary of State for Health," said Professor Kent Woods, MHRA chief executive.
"We are satisfied that the adverse incidents which occurred were not as a result of any errors made in the manufacture of TGN1412, its formulation, dilution or administration to trial participants."
However, the MHRA has accused global contract research firm Parexel of breaking a number of safety rules during the trial by failing to follow correct procedures and of making errors over contracts and patient records.
According to the report, Parexel did not adhere to documentation procedures during the trial.
"Parexel failed to complete the full medical background of a trial subject in writing - one principal investigator did not update the medical history file in writing following a verbal consultation with one of the volunteers," said the report.
Alarmingly, there was also no contract in existence for the bank-screening physician at the time they were employed (although one was subsequently issued). Parexel's principal investigator failed to authorise in their log the full work remit for the bank-screening physician at the start of their employment, the investigation found.
"Having interviewed the bank-screening physician as part of their inspection we were also not satisfied that the individual had adequate training and experience for their role," said the MHRA Inspectors.
At the time of the drama, the MHRA also found that Parexel was non-compliant with the unblinding procedure, meaning that the placebo volunteers were allowed to leave the trial before appropriate checks were taken to confirm that they were the two subjects that had received the placebo.
Surprisingly, prior to beginning the trial there was also no contract in place between TeGenero and Parexel, although again, one was subsequently issued, and there was only a draft contract in existence between Parexel and the private laboratory they had engaged.
In addition, Parexel had failed to review TeGenero's insurance policy to ensure that one was in place and that there were no exclusion categories within it that might impact upon their volunteers. There was also no formal system in place to provide 24-hour medical cover, the report stated.
Parexel is now required to provide a response to the MHRA with evidence of appropriate corrective action.
Commenting on the findings, Herman Scholtz, head of Parexel clinical pharmacology said: "It is inevitable that following a highly detailed examination of systems and documentation, there would be areas cited for improvement."
The company said it is "committed to continuous improvement" and is "reviewing ways to enhance its processes and systems," although would provide no further comment on the matter.