A leading Canadian researcher and the U.S. group Public Citizen are calling on the U.S. Food and Drug Administration to pull the plug on a major international drug trial, calling it unethical.

They say the TIDE trial, which is investigating the cardiovascular risks of the diabetes drug Avandia, should be stopped because there's enough evidence to show the drug is more dangerous than a similar drug, Actos, and both drugs are more dangerous than older diabetes drugs.

"It really does not make sense that this trial should continue," said Dr. David Juurlink, a researcher at Sunnybrook Health Sciences Centre in Toronto who conducted an earlier large study comparing the drugs.

That study, published last summer, found people taking Actos or pioglitazone for Type 2 diabetes are 23 per cent less likely to be hospitalized for heart failure and 14 per cent less likely to die than people taking Avandia or rosiglitazone.

At the time of its publication, Juurlink said, based on the findings, he could not think of a reason why a patient would agree to take Avandia or why a doctor would prescribe it.

Avandia is made by GlaxoSmithKline and Actos by Takeda Pharmaceuticals.

"Given the gathering cloud of data regarding the risk of rosiglitazone as compared to pioglitazone, what really is the 'big picture' purpose of this trial?" Juurlink asked in a release issued by Public Citizen.

"To see if the previous studies are right, and that rosiglitazone — which has no advantage over pioglitazone — really is more dangerous than pioglitazone? The need for certainty is not a reason to do a trial. These are patients, not guinea pigs."

FDA to reassess trial

The trial — called Thiazolidinedione Intervention in Vitamin D Evaluation or TIDE — is being conducted at 137 sites around the world, including 34 in Canada and six in developing countries.

The FDA said it was reviewing both the call from Public Citizen and the need for the TIDE trial.

"Some scientists and professional organizations, both inside and outside FDA, conclude that Avandia is inferior to Actos, based on the results from several well-designed observational trials and meta-analyses," spokeswoman Karen Riley said in an emailed response to questions.

"These scientists understandably have ethical concerns about the TIDE trial. Other FDA scientists and professional organizations, including the American College of Cardiology and the American Heart Association, have concluded that the issue of whether one drug is inferior to the other remains unresolved and therefore believe further study is necessary to answer important comparative safety questions."

"The TIDE trial will be discussed at a joint advisory committee in July. Based on expert input and our own analysis, FDA will reassess the rationale for the TIDE trial, review the trial's enrolment and respond accordingly."

The trial, which began last May, has already begun recruiting patients at 83 sites. The aim is to enrol 16,000 participants and the study is expected to run until 2015.