The drug behind the fury is called TGN1412, a monoclonal antibody being developed by Germany's TeGenero to treat conditions including multiple sclerosis, rheumatoid arthritis and leukaemia.
Parexel, which owns and operates the dedicated clinical research facility unit at the Northwick Park Hospital where the trial took place, was running the Phase I clinical trial under a contract with TeGenero. The scare is sending shockwaves throughout the clinical trials industry, where over 30 per cent of Phase I-III trials are outsourced, and may make it even harder to recruit study subjects in an industry that is already struggling to do so.
A Phase I trial tests a drug for the first time in a small group of healthy human volunteers to determine the drug's activity, including any potential side-effects.
Eight men took part in this stage of the clinical trial; six were given the product and two were given a placebo.
All six healthy volunteers who took TGN1412 experienced an unexpected adverse reaction and were admitted to intensive care with hours of taking the drug.
Two are in a critical condition, and the other four are serious but showing some signs of improvement, said Northwick Park Hospital's intensive care director Ganesh Suntharalingam.
"When the adverse reaction occurred, the Parexel clinical pharmacology medical team stopped the study procedures immediately and notified authorities," said Professor Herman Scholtz, head of Parexel International Clinical Pharmacology.
The trial was immediately suspended by the Medicines and Healthcare products Regulatory Agency (MHRA) who is now reviewing the data submitted with the application for the trial. The MHRA has also notified other European regulatory bodies of the danger.
It is likely that the MHRA will rule out any possibility of further clinical trials on the drug and according to a statement from TeGenero, "there is no further human testing of TGN1412 being pursued."
The MHRA has now also sent inspectors to the Parexel research unit to begin investigations and is working closely with the North West London Strategic Health Authority, Department of Health and Metropolitan Police.
What caused this tragedy is now a matter of speculation until the MHRA investigation is completed.
"We are not sure how long it will take to get to the bottom of this, but we expect it to be within the next few weeks, if not days," Sarah Coakley, MHRA spokesperson, told Outsourcing-Pharma.com.
"Something like this has never happened before," she said.
The investigation will now trawl through all aspects of the drugs lifecycle, including the product itself, the manufacturing process, how it was transported and stored and whether it was administered correctly.
"The cause of the adverse reactions could be anything from product contamination, to destabilisation during storage or human error during administration," said Coakley.
"This is the first time the drug has been given to humans and it is possible that by some "freak of nature" all the men reacted badly to it," she said.
Until the answer is known, the two companies at the eye of the storm remain under scrutiny.
"If any company is found negligent, we will consult our lawyers and proceed from there. I wouldn't like to speculate any further at this stage," said Coakley.
In a statement released on Wednesday, Dr Benedikte Hatz, CEO of TeGenero, stressed that "the clinical trial performed by Parexel adhered to standard clinical research guidelines."
"These events were completely unexpected and do not reflect the results we obtained from initial laboratory studies which enabled us to progress investigations into human volunteers," he said.
Aside from the obvious health concern of those involved, this incident has wider implications for the clinical trials industry, with many companies that run clinical trials already struggling to find patients to participate.
Patient recruitment consumes more time than any other clinical trial activity, with thirty per cent of clinical trial time spent finding and enrolling study subjects, and almost half of all trial delays result from patient recruitment problems, according to a new report published by market intelligence firm Cutting Edge Information.
As a result, the average Phase II and III clinical trial is lasting 30-42 per cent longer than planned, and in many cases, trials are being delayed by over six months, costing drug companies over half a million dollars for specialty products and more than $8m (€6.7m) for blockbuster brands in lost sales.
In addition to lost sales, these delays are causing the cost of running clinical trials to skyrocket to the tune of millions of dollars.
This week's drug scare will merely exacerbate the problem, driving fearful patients further from the grasp of pharma trials recruiters.
Furthermore, many pharma companies that are already nervous about handing over control of clinical trials to outsourcing companies may now pull back the reigns.