Drug Interactions Between Dificid, Lexapro And Zofran

In our latest question and answer, the pharmacist discusses potential drug interactions between meds received at the hospital.


My mom has been in and out of the hospital for the past month with diverticulitis, severe stomach pains, anxiety, and nausea. They just found out she now has c-diff and they put her on FIDAXOMICIN for that. But they also have her on Lexapro for anxiety and Zofran for nausea. Can these three drugs be taken together?

Asked by Pam On Oct 29, 2021

Answered by
Medical Content Reviewed By HelloPharmacist Staff

Published Oct 29, 2021
Last updated Sep 27, 2023

Key points

  • There are no known drug interactions between fidaxomicin and either escitalopram or ondansetron.
  • There is a potential drug interaction, QT prolongation, between escitalopram and ondansetron, but it is probably safe for your mother to take these together if she was taking them in the hospital.

Hi Pam and thank you for your great question. It looks like you are doing a great job keeping an eye out for your mom’s health.

It’s always a good idea to double-check that prescription medications are safe together, especially if new ones are started after a hospital stay.

The Drugs In Question

First, fidaxomicin, or by the brand name Dificid, is an effective treatment for Clostridium difficile (or C. diff) infections of the gut.

Only a very small amount of the medication is absorbed, so the majority of the dose stays in the GI tract. For this reason, it is generally well-tolerated and doesn’t have many drug interactions.

Next is Lexapro.

Lexapro (or under the generic name, escitalopram) is a selective serotonin reuptake inhibitor approved to help treat depression, generalized anxiety disorder, or a host of other conditions.

When it comes to escitalopram, most side effects tend to occur when the medication is started for the first time. Generally, these side effects gradually resolve and she’ll start to experience the positive effects of the medication after being on the medication for 4-12 weeks.

Lastly is Zofran (ondansetron). Zofran is a very effective nausea medication. We use it all the time in both the hospital and outpatient pharmacy world. It is cheap, effective, and generally well tolerated.


As I mentioned earlier, Fidaxomicin doesn’t get absorbed much, so there aren’t many drugs that interact with it that we worry about. There are no known interactions with it when combined with ondansetron or escitalopram.

Next, there is a drug interaction with escitalopram and ondansetron.

Interaction Between Zofran And Lexapro

Both medications (escitalopram and ondansetron) individually increase the “QT interval” and it increases even more when combined. Before I explain the QT interval and the risks, I imagine that your mother was taking this combination at the hospital.

I also imagine that at some point she had a baseline electrocardiogram which let the hospital staff evaluate her risk, and they felt comfortable with this combination of medication.

If she was on these medications in the hospital, the hospital team was comfortable with the combination, and it didn’t cause any issues during her stay, then it looks to be a safe treatment option for her. 

Back to QT interval.

Your heartbeat can be broken down into several parts. I’m sure that you’ve seen someone hooked up to an electrocardiogram; even in a movie or TV show.

Some medications can cause small changes to your heart rhythm. We are concerned here about some of your medications causing QT prolongation, or your heart taking a bit longer to recharge between beats.

Many medications cause this and it’s usually not a significant issue unless the person is on multiple medications that cause this, or has high-risk factors. If too much QT prolongation occurs, an arrhythmia can occur or even cardiac arrest.

The next question is does this matter for her? That is something that I don’t know. There are a few risk factors that you should be on the lookout for.

QT Prolongation Risk Factors

Is she on other medications that cause QT prolongation (you might need to ask your physician, pharmacist, or write us back)? Females are at greater risk. So are the elderly, and people with preexisting cardiac issues. It’s also dose-related. If she is planning on taking a single 4mg ondansetron once or twice a day, she is at lower risk. If she is routinely taking 8mg three times daily, your risk is increased.

Lastly, if she's had a recent electrocardiogram and her QT interval or QTc is below 450ms, then you should be safe to take the ondansetron. 

I hope this helps! Feel free to write us again in the future.


About the Pharmacist

Dr. Brian Staiger, PharmD

Dr. Brian has been practicing pharmacy for over 13 years and has wide-ranging experiences in many different areas of the profession. From retail, clinical, program development, and administrative responsibilities, he's your knowledgeable and go-to source for all your pharmacy and medication-related questions! Dr. Brian Staiger also has herbalist training and educational certificates in the field of medical ethnobotany. Feel free to send him an email at Hello@HelloPharmacist.com! You can also connect with Dr. Brian Staiger on LinkedIn.

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