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New drugs that are rushed through the approval process to meet government-imposed deadlines in the United States are much more likely to be the subject of recalls and safety problems, reveals a new study that sheds light on how these constraints affect decisions made by health officials.

Working within rigid deadlines may put too much pressure on health regulators, compromising their ability to focus adequate attention on the safety and efficacy of the drug, as well as the quality of clinical data submitted by the pharmaceutical company, according to the study published today in the New England Journal of Medicine.

"Deadlines are a part of life and they do a lot," said Daniel Carpenter, professor of government at Harvard University and lead author of the study. "The question is should we be relying so heavily on deadlines, or could we rely a little bit less on deadlines and a little more on resources?"

Major recalls and safety problems in recent years involving drugs such as Vioxx, Celebrex and Avandia have turned a spotlight on the drug approvals process. Health agencies in Canada and the United States have faced criticism over the fact drug companies pay them to review drugs, often under tight time restrictions.

Drug approval deadlines were introduced by the U.S. Food and Drug Administration in the early 1990s as part of a major overhaul of the regulatory process. The U.S. government began to charge "user fees" to drug companies to cover the bulk of the costs to conduct drug reviews. In return, the companies were promised speedier approvals. Approval deadlines vary, but generally range from six to 12 months.

At the time, critics warned that introducing deadlines could result in more unsafe drugs on the market. The new study seems to confirm those fears.

Although Canada doesn't have the same strict deadlines as the United States, Health Canada has been under mounting pressure to speed up approvals. The federal government is also preparing to introduce a new "progressive licensing" system that will allow drugs to be approved much more quickly so they can be monitored once they are on the market.

It is important for Canadians to have access to vital medications, but increasing pressure from the pharmaceutical industry for faster approvals is shifting the focus away from thorough premarket assessment of drugs, creating potential risks to consumers, said Joel Lexchin, health policy professor at York University and drug safety expert.

"We need to be paying much more attention to safety issues in the premarketing phase," he said. "If it's going to take an extra 100 days to do a thorough safety evaluation, we need to take that time. Once those drugs hit the market, currently Health Canada has very little control over what happens to them."

In the study, researchers found that new drugs approved by the FDA in the two months before the deadline were several times more likely to be the subject of product recalls or safety warnings after they became available to the public.

However, drugs approved more than two months before the deadline did not have an increased likelihood of safety problems, according to the study. That has led researchers to believe that it is deadline pressures - not the speed of drug approvals - that can lead to unsafe drugs making it to the market.

For instance, 14 drugs approved from 1993 to 2004 shortly before the deadline were later withdrawn from the market and/or subject of a serious health warning, compared with seven that were approved at other times.

"Deadlines may offer a blunt tool with which to accelerate review," said the study, adding that time restrictions "may also cause drugs approved under these constraints to have a higher likelihood of unanticipated safety problems once they are in widespread use."