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Canada Oral antifungal drug used to treat yeast infections linked to higher rates of miscarriage: study

A drug commonly used to treat yeast infections is linked to an increased risk of miscarriage in pregnant women, according to new Canadian research.

Pregnant women who took an oral version of the drug fluconazole, sold under brand names such as Diflucan One, were slightly more likely to experience a miscarriage than those who didn’t take the drug, according to a study published Tuesday in the Canadian Medical Association Journal. It’s unclear if the drug caused the miscarriages or if other factors were involved, but researchers say the findings are concerning enough that pregnant women should be told to avoid the oral version of fluconazole.

It’s the second study to identify a link between fluconazole and miscarriage in recent years. In 2016, a Danish study found that women who used oral fluconazole were slightly more likely to have a miscarriage than women who used the topical form of the drug. Health Canada did a safety review after that study came out and concluded there was not enough evidence to definitively conclude the risks are real. But product manufacturers have since updated the safety labels on the drug to warn women about the potential link to miscarriage.

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In the new study, researchers included more than 320,000 women who were pregnant in Quebec from 1998 to 2015. They compared women with clinically confirmed pregnancies who had taken oral fluconazole to those who hadn’t.

The miscarriage rate in the group that had not taken the yeast infection drug was about 6 per cent while it was about 12 per cent in the group that had taken the drug, said lead study author Anick Bérard, a professor of perinatal epidemiology at the University of Montreal. The increased miscarriage risk was present in women who took both low- and high-dose versions of fluconazole. There did not appear to be any increased risk of stillbirth or major abnormalities, she said.

Yeast infections are common among pregnant women, Dr. Bérard said, and about 10 per cent of pregnant women will experience one, which explains why the question over the safety of fluconazole is important. It’s believed that fluconazole could disrupt the normal flow of enzymes necessary for healthy fetal development.

“The bottom line is that women need to discuss this with their health-care physician,” she said.

A low-dose version of oral fluconazole is available over the counter. Vanessa Paquette, clinical pharmacy specialist at BC Women’s Hospital, said all pregnant women who think they have a yeast infection should get diagnosed by a health professional instead of using over-the-counter products to avoid the potential risks. It’s important for women to know the potential dangers of the yeast infection drug, especially since there are safe alternatives, such as topical medications.

“When we have a safe and effective alternative, we should be going with those,” Ms. Paquette said.

Kellie Murphy, head of clinical research in the women’s and infants’ program at Toronto’s Mount Sinai Hospital, said it’s important to remember it’s not clear whether fluconazole caused the miscarriage rate to be increased. The researchers didn’t have access to information on whether the women in the study smoked, drank alcohol or took folic acid as a vitamin supplement during pregnancy, so those and other factors could also help explain the miscarriage risk, Dr. Murphy said.

“I think the research needs to be interpreted in context,” she said.

Women who have taken fluconazole and experienced a miscarriage should not assume the drug was the cause, Dr. Murphy said.

Nav Persaud, a scientist at the Li Ka Shing Knowledge Institute at Toronto’s St. Michael’s Hospital, said that in these cases, it’s impossible to determine whether there’s a cause-and-effect relationship between the drug and miscarriage. It would be unethical to do a randomized controlled trial in which some pregnant women are prescribed fluconazole and some aren’t. Instead, researchers have to rely on observational studies, which look at what happened to large groups of women exposed to the drug compared to women who weren’t.

But based on the findings, women should be given alternative drugs and told the risks, he said.

“At the very least, I think if a clinician was advising a pregnant patient about treating a yeast infection, the patient should be advised of the potential harm of fluconazole,” Dr. Persaud said.

Editor’s note: An earlier version of this story incorrectly stated a Canadian study into the oral version of the drug fluconazole included data from 1998 to 2005. It has been corrected to state the data were from 1998 to 2015.
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