LONDON - Researchers should be more cautious in dosing experimental medicines in early human trials, even when drugs are thought to be low risk, experts reviewing a French clinical study that left one person dead said on Wednesday.

The volunteer died and five others became seriously ill in January after being given high doses of a novel painkiller made by Portuguese pharmaceutical company Bial in the first-into-human, or Phase I, clinical trial.

The study had undergone safety reviews but the new drug was not considered high-risk because it had already been tested in non-human primates and medicines with a similar mode of action had also been given previously to people without ill effect.

As a result, it was not considered necessary to use "sequential" dosing, which involves giving the first dose of a new compound to just one participant with a delay before treating others.

The lesson of the case was that better risk assessment and much more frequent sequential dosing should be used in future, according to an editorial by experts in the British Journal of Clinical Pharmacology.

"Unless additional information becomes apparent to say that there were unique features about this study, we are going to need to be much more careful in designing studies to sequentially dose patients," said Michael Eddleston of the University of Edinburgh, one of the authors.

"It is possible that all groups will need to be sequentially dosed."

Bial's medicine was a so-called FAAH inhibitor that works by targeting the body's endocannabinoid system, which is also responsible for the human response to cannabis.

Bial said at the time of the disaster that the trial had been approved by French regulators and it was committed to ensuring the wellbeing of test participants.

Cases of early-stage clinical trials going badly wrong are rare but not unheard of. In 2006, six healthy volunteers ended up in intensive care in London after being given a drug made by German biotech firm TeGenero. (Reporting by Ben Hirschler; editing by Susan Thomas)

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Researchers should be more cautious in dosing experimental medicines in early human trials, even when drugs are thought to be low risk, experts reviewing a French clinical study that left one person dead said on Wednesday.

The volunteer died and five others became seriously ill in January after being given high doses of a novel painkiller made by Portuguese pharmaceutical company Bial in the first-into-human, or Phase I, clinical trial.

The study had undergone safety reviews but the new drug was not considered high-risk because it had already been tested in non-human primates and medicines with a similar mode of action had also been given previously to people without ill effect.

As a result, it was not considered necessary to use "sequential" dosing, which involves giving the first dose of a new compound to just one participant with a delay before treating others.

The lesson of the case was that better risk assessment and much more frequent sequential dosing should be used in future, according to an editorial by experts in the British Journal of Clinical Pharmacology.

"Unless additional information becomes apparent to say that there were unique features about this study, we are going to need to be much more careful in designing studies to sequentially dose patients," said Michael Eddleston of the University of Edinburgh, one of the authors.

"It is possible that all groups will need to be sequentially dosed."

Bial's medicine was a so-called FAAH inhibitor that works by targeting the body's endocannabinoid system, which is also responsible for the human response to cannabis.

Bial said at the time of the disaster that the trial had been approved by French regulators and it was committed to ensuring the wellbeing of test participants.

Cases of early-stage clinical trials going badly wrong are rare but not unheard of. In 2006, six healthy volunteers ended up in intensive care in London after being given a drug made by German biotech firm TeGenero.