What happens when you take saccharomyces boulardii with antifungals?
Saccharomyces boulardii is a live yeast probiotic, sold under brand names such as Florastor and used for traveler's diarrhea, antibiotic-associated diarrhea, and recurrent Clostridioides difficile infection. Despite being marketed as a probiotic, it is biologically a yeast, closely related to baker's yeast (Saccharomyces cerevisiae). Systemic antifungals are designed to kill yeast, which sets up the conflict.
- You swallow a live yeast. A Florastor-type capsule delivers viable S. boulardii cells to the gut, where they are meant to survive and exert a probiotic effect.
- The antifungal attacks yeast cells. Azoles (fluconazole, itraconazole, voriconazole, posaconazole) block an enzyme needed to build the yeast cell membrane. Polyenes (amphotericin B, nystatin) punch holes in the membrane. Echinocandins (caspofungin, micafungin, anidulafungin) disrupt the yeast cell wall.
- S. boulardii is not spared. All three classes are active against this yeast just as they are against pathogenic Candida. The probiotic organism is collateral.
- The combination cancels itself out. The antifungal kills the probiotic before it can act, so you carry the cost and swallowing burden of a supplement that delivers no benefit while you are on therapy.
- And it may add risk. Living yeast in the gut of someone already being treated for a fungal threat introduces a documented infection hazard rather than a benefit.
Why is this important?
This is not just a wasted supplement. S. boulardii has caused fungemia, a bloodstream infection from the probiotic organism itself. A review by the CDC's Emerging Infectious Diseases journal found the probiotic was implicated in a substantial share of S. cerevisiae/boulardii bloodstream infections, with use of the supplement strongly associated with infection. The danger concentrates in identifiable groups.
The risk is highest in intensive-care patients, people with central venous catheters, immunocompromised patients, and preterm infants. Anyone on systemic antifungals is, almost by definition, already in a setting where opportunistic yeast infection is a real concern, so adding more live yeast to the gut stacks risk without offering benefit.
There is also a delayed hazard. Once the antifungal stops, residual S. boulardii can regrow, and if it crosses a damaged gut wall it may cause invasive disease that outlasts the prescription. The case literature is strong enough that hospital pharmacies frequently restrict S. boulardii in critically ill patients and patients with central lines, even when an antifungal is already on board.
What should you do?
The conflict is straightforward to manage, but the timing matters.
Before you start the antifungal: Stop taking Saccharomyces boulardii products such as Florastor and tell the prescribing physician you were using one. Ask whether a bacterial probiotic could substitute if a probiotic is still wanted, since Lactobacillus and Bifidobacterium species are not directly killed by azole antifungals.
While you are on therapy: Do not take S. boulardii in any form. If you are admitted to a hospital and a clinician asks about home supplements, mention any probiotic explicitly. Florastor capsules look unremarkable and are easy to overlook, but they are clinically meaningful. If you have a central venous catheter, port, or PICC line, do not handle the capsules near the catheter site, because contamination has been linked to fungemia.
After the course ends: Do not restart S. boulardii on your own. Wait until your clinician confirms it is safe, particularly if you were critically ill, immunocompromised, or catheterized. Review the decision with your doctor or pharmacist.
Which specific products are affected?
Probiotics to stop include Florastor, Florastor Kids, DiaResQ, and any supplement listing Saccharomyces boulardii, S. cerevisiae var. boulardii, or generic Saccharomyces cerevisiae. Some multi-strain probiotic blends include S. boulardii alongside bacterial species, so read the ingredient panel carefully.
Antifungals of concern include fluconazole (Diflucan), itraconazole (Sporanox), voriconazole (Vfend), posaconazole (Noxafil), ketoconazole, amphotericin B, caspofungin (Cancidas), micafungin (Mycamine), and anidulafungin (Eraxis).
Topical antifungals such as clotrimazole or terbinafine cream have negligible systemic exposure and do not interact with oral S. boulardii. Oral nystatin used as a swish-and-spit for thrush has minimal systemic absorption but can still reduce S. boulardii viability in the upper gut, so ask your prescriber.
The science behind it
The concern rests on documented case evidence, not theory.
- Rannikko J, et al. Emerging Infectious Diseases (CDC), 2021;27(8). This review of Saccharomyces fungemia and other fungal infections found the S. boulardii probiotic was associated with a large share of cases and that use of the supplement carried a strong association with bloodstream infection, concentrated in vulnerable hospitalized patients. Read it here.
- Saccharomyces boulardii fungemia following probiotic treatment (case report), PMC3316799. A documented instance of bloodstream infection developing in a patient given the probiotic, illustrating the real-world mechanism. Read it here.
That this is a yeast killed by antifungals is established microbiology; the published cases above show why the combination matters clinically in at-risk patients.
Frequently Asked Questions
Will the antifungal stop working if I take Florastor too?
No. Your antifungal will still treat your infection. The problem runs the other way: the antifungal kills the probiotic yeast, so you get no probiotic benefit, and adding live yeast may raise infection risk in vulnerable patients.
Can I just take Florastor a few hours apart from my antifungal?
Separating the doses does not fix this. Systemic antifungals circulate throughout the body for the whole course, so the yeast is exposed regardless of timing. The issue is the overlap of the therapy, not the spacing of pills.
Is it safe if I am otherwise healthy?
The serious fungemia risk concentrates in critically ill, immunocompromised, catheterized, and preterm patients. Even so, if you need a systemic antifungal at all, taking S. boulardii alongside it has no upside, so stopping it and telling your prescriber is the sensible course.
What probiotic can I take instead?
Bacterial probiotics such as Lactobacillus and Bifidobacterium species are not directly killed by azole antifungals and may be an option. Ask your doctor or pharmacist whether one is appropriate for your situation.
Do antifungal creams or thrush rinses count?
Topical creams like clotrimazole or terbinafine have negligible systemic exposure and do not interact with oral S. boulardii. Oral nystatin swish-and-spit has minimal systemic absorption but can still reduce the probiotic's viability in the upper gut, so confirm with your prescriber.
When can I restart Florastor after my antifungal course?
Do not restart on your own. Wait until your clinician confirms it is safe, especially if you were hospitalized, immunocompromised, or had a central line.
Key takeaways
- Saccharomyces boulardii is a live yeast, and systemic antifungals are designed to kill yeast, so the combination cancels the probiotic benefit.
- The combination can also be dangerous: S. boulardii has caused documented bloodstream infections, mostly in critically ill, immunocompromised, catheterized, or preterm patients.
- Stop the probiotic during antifungal therapy and tell your prescriber you were taking it.
- A bacterial probiotic (Lactobacillus or Bifidobacterium) may substitute; do not restart S. boulardii until your clinician confirms it is safe.
- Review the decision with your doctor or pharmacist.