What happens when you take probiotics with antifungals?
Probiotics fall into two broad categories. The first is bacterial probiotics, which include Lactobacillus, Bifidobacterium, and Streptococcus thermophilus. The second is yeast-based probiotics, which are dominated by Saccharomyces boulardii, the active organism in products such as Florastor. Antifungal medications are designed to kill or inhibit fungi, including yeasts.
The result is straightforward chemistry. A systemic antifungal such as fluconazole, itraconazole, voriconazole, posaconazole, amphotericin B, or an echinocandin will attack Saccharomyces boulardii in exactly the same way that it attacks pathogenic Candida species. Co-administering a yeast probiotic with an antifungal therefore makes the probiotic less viable, often killing it before it can colonize the gut. Bacterial probiotics, on the other hand, have very different cell walls and metabolism and are not directly killed by azole antifungals. Some Lactobacillus strains have even been studied as adjuncts to fluconazole for recurrent vaginal candidiasis.
Why is this important?
People often turn to probiotics precisely when they are sick with conditions that may also involve antifungal therapy, such as recurrent thrush, vaginal yeast infections, or candida overgrowth after antibiotics. Taking Saccharomyces boulardii alongside fluconazole feels intuitive but is mechanistically self-defeating. The patient is taking one product specifically to kill yeast and another product that is itself a yeast.
There is also a safety dimension. The published literature, including a CDC Emerging Infectious Diseases review and case series, has documented Saccharomyces boulardii fungemia in immunocompromised patients and in patients with central venous catheters. When a patient on antifungal therapy continues to take a yeast probiotic, the antifungal may be the only thing preventing systemic spread. If the antifungal is stopped before the probiotic is cleared, the risk of fungemia rises.
For bacterial probiotics the situation is more benign. In vitro and clinical studies suggest that Lactobacillus and Bifidobacterium are not significantly affected by azole antifungals. There is even evidence that bacterial probiotics can help suppress Candida overgrowth, complementing antifungal therapy rather than fighting it.
What should you do?
If you are prescribed a systemic antifungal such as fluconazole, itraconazole, voriconazole, posaconazole, amphotericin B, caspofungin, micafungin, or anidulafungin, stop any product that contains Saccharomyces boulardii, Saccharomyces cerevisiae, or other yeast probiotics. Check supplement labels carefully; some multi-strain probiotics include a yeast component alongside bacteria.
If you take a bacterial probiotic such as a Lactobacillus or Bifidobacterium blend, you can usually continue it through a course of antifungal therapy, although some clinicians suggest spacing the dose two to three hours away from the antifungal as a precaution. Ask the prescriber what is preferred. Topical antifungals such as clotrimazole or terbinafine cream do not interact meaningfully with oral probiotics, because there is no systemic exposure.
If you are immunocompromised, on chemotherapy, or have a central venous catheter, avoid Saccharomyces boulardii entirely regardless of antifungal use because of the documented risk of fungemia.
Which specific products are affected?
Yeast probiotic products of concern include Florastor, DiaResQ, and any supplement listing Saccharomyces boulardii or S. cerevisiae var. boulardii as an ingredient. Antifungals of concern include the azoles (fluconazole, itraconazole, voriconazole, posaconazole, ketoconazole), polyenes (amphotericin B, nystatin when taken systemically), and echinocandins (caspofungin, micafungin, anidulafungin).
Bacterial probiotic products containing only Lactobacillus, Bifidobacterium, Streptococcus, or Bacillus strains are generally compatible with antifungal therapy. Common multi-strain blends and yogurt-based products fall here.
The bottom line
Yeast and antifungals do not mix. Bacteria and antifungals can. Switch to a bacterial-only probiotic, or pause your probiotic, while you are on systemic antifungal therapy, and resume your yeast probiotic only after the antifungal course is complete and your prescriber agrees.