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Previously unpublished information from clinical trial pivotal to FDA approval calls into question effectiveness of pregnancy anti-nausea drug

Toronto, January 17, 2018

By Leslie Shepherd

Dr. Nav Persaud
Dr. Nav Persaud

Previously unpublished information from the clinical trial that the U.S. Food and Drug Administration relied on to approve the most commonly prescribed medicine for nausea in pregnancy indicates the drug is not effective, a new report says.

Researchers at St. Michael’s Hospital obtained thousands of pages of documents from Health Canada relating to the randomized clinical trial that was reported in 2010 as showing pyridoxine-doxylamine was effective in reducing nausea and vomiting in pregnancy.

The trial found that on a 13-point scale, women who took the drug sold as Diclectin in Canada (Diclegis in the United States) reported symptom reductions that were 0.7 points greater than women who took a placebo.

But Dr. Nav Persaud, a researcher and family physician at St. Michael’s, said the manufacturer’s detailed 9,000-page “clinical study report” he obtained from Health Canada specified that the findings would be clinically important only if there were a three-point reduction in symptoms.

“That information was hidden until now,” he said.

His analysis was published today in the online journal PLOS ONE.

Dr. Persaud said that while the findings reported in 2010 may be statistically significant, they were not large enough to be noticeable by women taking the medication. By the end of the two-week trial, most women given a placebo had little or no symptoms.

Dr. Persaud said there was also “selective reporting” of secondary outcomes in the 2010 publication that made Diclectin appear effective. The 2010 paper indicated apparent benefits of the drug such as a reduction in the time lost from employment due to nausea and vomiting. But the 2010 publication did not include outcomes where there was no difference between the two groups, such as time lost from household tasks or number of visits to health-care providers.

The clinical trial was sponsored by Duchesnay Inc., the manufacturer of the drug. It was conducted at six university medical centres in the United States. The published results were based on 101 women who took pyridoxine-doxylamine and a control group of 86 women; the original enrollment was higher, but many women dropped out during the trial.

Dr. Persaud said that when Duchesnay approached the FDA in the early 2000s to approve pyridoxine-doxylamine, the regulatory agency said it needed evidence from a clinical trial. The FDA approved the drug in 2013, after this trial was done, and it has been prescribed in 33 million women worldwide according to the company. There is at least one prescription filled for every two births in Canada.

In the 1980s, the drug was voluntarily withdrawn from the American market in the midst of legal claims about birth defects that were eventually rejected by courts. Recently, Kim Kardashian was censured by the FDA for inappropriately promoting the drug on social media.

Dr. Persaud said the FDA should revisit its decision, as should Health Canada and provinces that offer the drug through publicly funded prescription drug plans. Clinicians could stop prescribing it and pregnant women could seek effective treatments instead of this drug, he said.


This paper is an example of how St. Michael's Hospital is making Ontario Healthier, Wealthier, Smarter.

About St. Michael's Hospital

St. Michael’s Hospital provides compassionate care to all who enter its doors. The hospital also provides outstanding medical education to future health care professionals in more than 29 academic disciplines. Critical care and trauma, heart disease, neurosurgery, diabetes, cancer care, care of the homeless and global health are among the Hospital’s recognized areas of expertise. Through the Keenan Research Centre and the Li Ka Shing International Healthcare Education Centre, which make up the Li Ka Shing Knowledge Institute, research and education at St. Michael’s Hospital are recognized and make an impact around the world. Founded in 1892, the hospital is fully affiliated with the University of Toronto.


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