The most commonly prescribed drug for first-trimester morning sickness, pyridoxine-doxylamine, does not prevent birth defects even though drug safety data say it does, according to researchers.
The drug is so popular that it has been prescribed to 33 million women worldwide and is used in half of pregnancies in Canada that result in live births. The Society of Obstetricians and Gynecologists of Canada lists it as the standard of care for women with nausea and vomiting “since it has the greatest evidence to support its efficacy and safety.”
“When prescribing the drug to one of my patients she had a lot questions,” says Nav Persaud, a family and community medicine physician at St. Michael’s Hospital and lecturer at the University of Toronto. “I found myself making strong statements about its safety and realized that I should know more.”
Persaud went back and looked at all of the data that led to pyridoxine-doxylamine’s top safety ranking. Persaud found that the number of patients that were part of the original studies wasn’t more than 200,000, as previously stated, but was closer to 130,000.
The drug’s safety data—numbers that clinicians still cite and use today—say that the use of the drug decreased the risk of birth defects such as limb malformation or congenital heart defects.
“The numbers didn’t add up,” says Persaud, a scientist in the hospital’s Li Ka Shing Knowledge Institute. “Despite claims that it reduced the risks of birth defects, data was much closer to natural average of birth defects—between three and five percent of all pregnancies.”
The commentary, published in Journal of Obstetrics and Gynaecology Canada, examines the primary studies that formed the basis of the Canadian guideline recommendations for pyridoxine-doxylamine. After reviewing the reports and studies, Persaud says he found the evidence lacking.
“The guidelines should change,” says Persaud.
Anti-nausea alternatives exist and are already used more frequently in other parts of the world. Pyridoxine, without doxylamine, has stronger safety data supporting it, but is prescribed less often.
Persaud says he was concerned that some patients may still prefer taking pyridoxine-doxylamine because they used it in previous pregnancies or because they’ve read about its safety and know the drug is considered standard of care.
“Vitamin B6 is similarly effective at treating nausea and vomiting in pregnancy,” says Persaud. “I’ve changed my practice and now recommend alternatives to pyridoxine-doxylamine that have been demonstrated to be safe.”
Source: University of Toronto