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Nearly a quarter of the new drugs approved in Canada eventually get a serious safety warning or have to be pulled from the market for safety reasons, according to a new study.

And for medications that get the fast-track "priority review" by the country's health regulator, the chance that a serious safety concern will surface is as high as a third, said Dr. Joel Lexchin, whose analysis was published this week in the Archives of Internal Medicine.

"It seems most likely that if you try and approve drugs too quickly, you may miss things or you may not have the time to fully understand the evidence," Lexchin said.

The findings add to evidence from the United States, where about a fifth of approved drugs acquired a "black box" safety warning or were recalled over a 25-year period, according to one study.

One recent example is Merck & Co's painkiller Vioxx, which was recalled in 2004 after it became clear that the drug had dangerous side effects and may have caused thousands of deaths.

Lexchin's study includes 434 new medications approved in the period from 1995 to 2010, 16 of which were subsequently recalled. Of the approved drugs, 112 got a priority review, which lasts 180 days instead of the typical 300 days.

The researcher, a health-policy professor at York University in Toronto, said Health Canada, like its U.S. counterpart, considers drugmaker data on new drugs confidential and does not release them for independent review.

"We are really not in a position to see whether Health Canada is doing a good job or not," Lexchin said. "I think Health Canada is failing consumers in that it doesn't make its information public."

When contacted about the report, Health Canada referred to a letter it had written to The Toronto Star about the findings. "Health Canada's priority review policy helps deliver treatments for serious, life threatening and severely debilitating diseases to patients sooner when no other drug is available to help," the letter says. "The fact that new drugs used to treat high-risk conditions are more frequently updated for new risk information is not unexpected."

It goes on to say that "drugs reviewed under the standard and the expedited processes are reviewed under the same regulatory framework – the level of scrutiny and the rules applied remain identical."

A commentary published along with the study points to the high human cost of errors in drug evaluation.

"Casualties in pharmaceutical disasters are measured in tens of thousands," writes Thomas Moore of the Institute for Safe Medication Practices in Horsham, Pa. "Getting faster access to newly developed, less thoroughly tested drugs is at best a mixed blessing," he adds. "For the first three years after approval, new drugs should carry a special warning akin to the black triangle used in Britain. It should be prominent and mean to every physician, New Drug: Caution Indicated."

Lexchin added this advice to patients: "What I would be asking my doctor is, 'How long has the drug been available?' And if it has not been available for very long, I would ask, 'Is there something that has been on the market longer that is just as good, and would you mind prescribing that?' "