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Studies Show Birth Defect Risk with Zofran Use During First Trimester of Pregnancy

Dec 14, 2015

GlaxoSmithKline's nausea and vomiting medication Zofran (ondansetron hydrochloride), is approved by the Food and Drug Administration (FDA) for use in the prevention of nausea and vomiting associated with chemotherapy and radiation therapy, and to prevent these symptoms following surgery.

Though not approved for use during pregnancy, Zofran is often prescribed to pregnant women who experience nausea and/or vomiting. Prescribing of medications for non-approved uses is known as "off-label" prescribing. Physicians may prescribe a drug for any purpose they see fit, though drug manufacturers may not promote a drug except for FDA-approved uses.

Up to 80 percent of women experience nausea and vomiting-morning sickness-in early pregnancy. In about 15 percent of pregnant women, the nausea and vomiting is serious enough to require medication, Medscape Multispecialty reports. Nausea and vomiting usually peak during the first trimester and subside thereafter, but, unfortunately, the first trimester is when there is the greatest danger that medications will have harmful (teratogenic) effects on the developing fetus. Studies on the effects of ondansetron on the developing fetus are limited and there are conflicting findings, but some findings suggest the need for caution in prescribing Zofran to pregnant women.

Canadian and Australian researchers published studies in 2004 comparing rates of miscarriage, stillbirth, and major birth defects among pregnant women taking ondansetron, other antiemetics, or no antiemetics; there were 176 women in each group. The women in the group that took ondansetron were all in the first trimester of pregnancy. The researchers found no significant differences among the groups for adverse pregnancy outcomes. But this was an industry-sponsored study that was powered to detect only a 3.5-fold or greater increased risk in major birth defects, Medscape Multispecialty reports. A larger, case/control study associated ondansetron with a 2.4 times higher risk for cleft palate with maternal use of ondansetron during the first trimester. Australian researchers who compared 251 pregnant women exposed to ondansetron from 2002 to 2005 with 96,717 women who were not exposed found a 20 percent increased risk for a major birth defect among infants exposed to ondansetron during the first trimester.

Danish researchers examined 1997 to 2010 data from the Medical Birth Registry and National Patient Register to evaluate the teratogenic effects of ondansetron during the first trimester. Of 897,018 births, prescription records indicate that 1,248 women were exposed to ondansetron. The odds of fetal heart malformation were two times as high in infants of women who took ondansetron compared with women who did not take the drug.

Swedish researchers looking at data from the Swedish Medical Birth Register and Swedish Register of Prescribed Drugs found 1,349 women exposed to ondansetron in early pregnancy from1998 and 2012. While ondansetron exposure was not associated with an increased risk for severe birth defects, the odds of general heart defects were 1.6 times higher, and the odds of heart septum defects were 2.1 times higher.

Under current guidelines from the FDA and Health Canada, Zofran is not recommended as the first-line option for treating nausea and vomiting in pregnancy, Medscape Multispecialty reports. If lifestyle and dietary modification are not effective, doxylamine/pyridoxine (Diclegis) has FDA approval for treating nausea and vomiting in pregnancy. Given the current evidence, ondansetron should be avoided in the first trimester of pregnancy unless other treatments are ineffective.

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