Is ondansetron (or Zofran) safe for my baby?

Stop by any early pregnancy forum and you are bound to run into this question, “Is ondansetron safe for my baby?”.

It’s usually asked by some poor woman desperately ill with severe morning sickness, or worse hyperemesis gravidarum.

She is most likely feeling awful and hopeless and trying to decide whether this drug will play a role in managing her pregnancy sickness.

ondansetron safe for my baby?

So what is the debate all about?

The question “Is ondansetron safe for my baby?” almost always strikes up a fierce and emotionally charged debate. The most passionate responses often come from women sitting in one of three camps:

Camp 1: I took it and my child / kids are fine. It’s perfectly safe to use. Doctors wouldn’t prescribe it if it wasn’t safe. Take the drug!

Camp 2: I or someone I know who took Zofran during pregnancy, and the baby ended up with a birth defect / I had a miscarriage. Don’t even think about taking the drug! You’ll never forgive yourself if something goes wrong.

Camp 3: The debate is irrelevant. My pregnancy sickness was so bad I wouldn’t have made it through my pregnancy without Zofran (or ondansetron). I mean I literally wouldn’t have made it. Take it if you need it.

Emotions run wild, the debate goes crazy and the original poster, who is looking for answers, more often than not leaves the forum even more confused and anxious (and still sick).

What are the actual claims being made?

It boils down to this, a bunch of women who took Zofran during pregnancy had babies with birth defects. Zofran is a particular brandname of ondansetron (so ondansetron is the generic name of the drug).

These women (and their lawyers) think Zofran is responsible for the birth defects. As a result, there are currently numerous lawsuits in the US specifically involving the company GlaxoSmithKline that makes Zofran.

Ondansetron safe for my baby

There are claims that GlaxoSmithKline knew the drug could be harmful when used during pregnancy, and that they provided misleading information about the safety of the drug.

There are claims that the company promoted the anti-nausea medicine to pregnant women even though the drug didn’t have FDA* approval.

There are also claims that the company gave kick backs to medical professionals for promoting Zofran to pregnant women (in the US).

So what do we actually know about pregnancy and Zofran?

Here is a summary of what we know. We have:

  • A pharmaceutical company behaving unethically at best, criminally at worst;
  • Some babies with birth defects who were exposed to Zofran during pregnancy;
  • There are conflicting conclusions from studies and limited safety data;
  • There is no super obvious reason to believe the drug causes harm (it’s still classed as a category B1** drug here in Australia).

Here are the specifics

Dodgy business practices

In 2012, the U.S. Department of Justice filed criminal and civil claims against GlaxoSmithKline.

The company was accused on misbranding drugs and failing to supply safety data to the FDA. They pleaded guilty and paid a cool $1 billion. There was also $2 billion settlement for civil liabilities with individual states and the federal government for fraud. This isn’t directly related to the Zofran lawsuit, but it’s enough to make you feel uncomfortable. It certainly puts a big fat dark cloud over the pharmaceutical company, and its ethics and practices.

No solid data

In terms of specific claims around Zofran and birth defects, things are less clear cut.

Much information around using Zofran in pregnancy comes from a study conducted on Danish Registry Data. A study published in Reproductive Toxicology found that Zofran didn’t increase the overall number of defects but did increase the likelihood of a particular heart defect called a septal defect.

But the analysis is far from definitive.

First of all, it’s a retrospective study, looking at the basic data captured in the registry. What other factors were at play?

It’s also a very small pool of women. The data used included 1.5 million births, of which 1326 pregnancies used Zofran in the 1st trimester. It was found that a particular heart defect occurred in 0.7% of babies not exposed to Zofran and 1.26% of babies exposed to Zofran. The authors concluded Zofran should be avoided in pregnancy based on these results. It’s about double the number of defects right? But when you look at the numbers, we are talking about a very small percentage.

Altogether the study looked at 17 babies exposed to Zofran with birth defects. 2/3 of the pregnant women involved took Zofran after being 8 weeks pregnant (the defect may have developed prior to this) and we don’t know what dosage was involved.

Another study (which was published in the New England Journal of Medicine) looked at the same data and concluded there is no correlation between Zofran and birth defects.

Talk about confusing.

The drug works

We also need to remember that Zofran appears to be one of the most effective drugs around for managing pregnancy sickness.

So. Should you take ondansetron?

So that brings us back to burning question, is ondansetron safe for my baby? And should you take it?

My best answer, find a doctor you like and really trust (and who is super competent too). Have them lay out all the risks, looking at what we know about the drug, your pregnancy and baby health and any other risk factors at play.

Then, when all the information is on the table, make a decision together.

Whatever you do, don’t make a call based on a pregnancy forum debate. Not in isolation anyway.

Stories on forums like this matter, they involve real women with real experiences and can give you all sorts of insight a doctor never will. But they don’t always give the full picture or consider all the information relevant to you, your body and your baby.

Why is it so hard to know for sure whether Zofran causes defects?

It’s an important question, “Is ondansetron safe for my baby?”. So why isn’t there a rock solid answer?

On face value it seems pretty straight forward, but once you dive into the data behind the debate, it gets cloudy pretty quickly. The tricky bit is that correlation doesn’t mean cause. Yes, women who took Zofran had babies with birth defects.

But did Zofran cause the defects? How can you know for sure?

It is thought that 2-3% of babies are born with birth defects. There are many risk factors that may play a role. This includes obesity, smoking, other lifestyle factors, having multiples, taking other medication. Genetics may play a role as well. Pinpointing the cause of a birth defect is very difficult.

A very clear cluster of defects in babies where the pregnant woman took a medication (as was the case with thalidomide) would make it possible to identify a cause. Very clear evidence from an animal study would also help make the link, but then it’s always possible that a particular drug can cause birth defects in humans but not animals (and the other way around). Neither of these types of clear cut data exist in the case of Zofran and pregnancy.

To know for sure, you’d really need many thousands of women to participate in a study. That’s not going to happen. Could you imagine being pregnant and saying “Yes please, sign me a up for a Zofran trial and we’ll see if it damages my child causing life long health challenges.” Imagine the ramifications if the company selling the drug conducted such a study and outcome was “yes, Zofran causes birth defects”. Aside from the harm to participants, there would be (very costly) legal ramifications as well. No pharmaceutical company would put themselves at that kind of risk.

Most of the data available about using Zofran in pregnancy comes from birth registries. The problem with this is that while such registries are often used to extrapolate data around drug safety, they are typically not intended or designed for this purpose. This lets data analysis get messy pretty quickly. If you conduct a study on the data, depending how the data is manipulated, it has the potential to yield different results from another study performed on the same data set.

* The FDA is the Food and Drug Administration in the US. It is a government body that has a similar role to the TGA (Therapeutic Goods Administration) in Australia.

** The legal action hasn’t changed the classification of Zofran in Australia. The drug is listed as a Category B1. According to the TGA, this means it’s a “Drug that has been taken by only a limited number of pregnant women and women of childbearing age, without an increase in the frequency of malformation or other direct or indirect harmful effects on the human fetus having been observed. Studies in animals have not shown evidence of an increased occurrence of fetal damage”.