Pregnancy and Nausea: Which medications are safe and effective to use?Andrea Huston
It may come as no surprise that up to 80% of women experience nausea during pregnancy, especially in the early stages. Severe nausea and vomiting is a reason for higher rates of pregnancy termination. So, it follows that the early, effective, and safe treatment of nausea is crucial for both the mother’s and the infant’s health. Because medications are prescribed to manage vomiting and nausea in the first trimester (when fetus development is most sensitive to toxins), pregnant women and clinicians often have concerns about the potential effects of anti-nausea or antiemetic drugs.
Malformations at birth are exceptionally rare, so finding the cause and effect of a single drug and resulting abnormality is extremely difficult. A recent study of 1.8 million pregnancies showed a direct correlation between the use of specific anti-nausea medications with a risk of birth abnormalities. Due to these concerns, Health Canada recommends NOT to use ondansetron (Zofran) for managing nausea during pregnancy. Pharmacogenetics, the study of how a person’s genetics and medications interact, can check whether commonly used anti-nausea drugs will be effective for an individual’s metabolism. Drugs such as dolasetron, ondansetron, palonosetron, and tropisetron can have varied effectiveness from person to person based on genetics. Pharmacogenetics may also help to understand the risks associated with these drugs.
The developing fetus is very sensitive to chemicals that can induce birth abnormalities. Thalidomide, used as a sedative and anti-nausea drug during the 1960s, is the most notorious example of how a seemingly innocent morning sickness medication turned into a horror story when drug-induced malformations became clear in children whose mothers took this drug during pregnancy. All drugs are now screened to reduce risks for pregnant women and their children, however, they all carry some risk of inducing birth abnormalities.
Many modern anti-nausea medications such as dolasetron, ondansetron, palonosetron, and tropisetron are considered safe for use during pregnancy. However, a recent study detected a small yet statistically significant increased risk of oral clefts with first trimester exposure to ondansetron (1912 abnormalities were found among unexposed infants and 124 abnormalities among exposed infants; adjusted risk difference, 2.7; 95% CI, 0.2 to 5.2 per 10 000 births). The authors found no difference in the risk of cardiac or overall birth abnormalities for infants of women exposed to ondansetron.
Ondansetron and other similar anti-nausea medications are metabolized by a specific enzyme called cytochrome CYP2D6. It is well known that women who are Ultrarapid CYP2D6 metabolizers do not respond to dolasetron, ondansetron, palonosetron, or tropisetron because the medication is cleared from the body too fast. These women need different anti-nausea medications. Please note that other antiemetic drugs, such as nabilone, which is a synthetic form of THC (the active ingredient in marijuana) , should not be used for nausea treatment in pregnant women. On the other hand, women who are Poor CYP2D6 metabolizers clear ondansetron and similar medications much slower, causing drug buildup in the bloodstream which may be toxic to the fetus. Although current clinical guidelines do not specify whether poor metabolizers need a dose reduction. Knowing your pharmacogenetic profile may help to improve nausea management, and aid in avoiding potential drug toxicity that may have a negative impact on developing infants.
Pharmacogenomics can help guide therapeutic choices for nausea, depression, pain management, and other areas of women’s health. Women who are Ultrarapid CYP2D6 metabolizers should not use codeine and other opioid painkillers while breastfeeding because of an elevated risk of infant death. Furthermore, a sizeable number of women suffer from post-partum depression and may need treatment with antidepressants, most of which also have strong pharmacogenetic interactions. Pillcheck uncovers your pharmacogenetic profile using a simple cheek swab and can give useful insights for ondansetron and other drugs used for nausea and vomiting. Click here to search for medications reported by Pillcheck. You can bring your Pillcheck results to your healthcare provider to personalize treatment for improved outcomes.