Saccharomyces boulardii

What is Saccharomyces boulardii

The yeast species Saccharomyces boulardii is a different species from the Brewer’s yeast species of S. cerevisiae or S. carlsbergensis (also known as S. pastorianus). This yeast is non-pathogenic in most persons, is not a normal inhabitant of the human bowel microflora, and is found naturally on the skin of certain fruits, such as lychee fruit and mangosteens.

The probiotic preparations of Saccharomyces boulardii are purported to reestablish the normal physiologic and bacterial flora of the intestinal tract. The products are administered orally as dietary supplements to support intestinal health, and are used off-label in the treatment of uncomplicated diarrhea, particularly that caused by modification of the intestinal flora by antibiotics.

Although not FDA-approved drug products and regulated as dietary supplements, probiotic products of Saccharomyces boulardii (e.g., Florastor products) have seen widespread in clinical use, following some controlled trials of its success in preventing antibiotic associated diarrhea (AAD).

Along with Lactobaccilus sp. (Saccharomyces boulardii has also been used as a co-strategy in prevention of clostridium difficile associated diarrhea (CDAD) and infection, particularly in relapsed cases.  A “lyo” suffix after the species name in the ingredient of select products refers to lyophilization of the yeast in product preparation.

Brand Names

  • Florastor
  • Florastor Kids
  • ReZyst Probiotic
  • ReZyst SB


  • diarrhea
  • nutritional supplementation

Side Effects

  • constipation
  • fever
  • flatulence
  • infection
  • nausea
  • polydipsia
  • vomiting

Monitoring Parameters

  • laboratory monitoring not necessary


  • acquired immunodeficiency syndrome (AIDS)
  • breast-feeding
  • central venous catheter placement
  • children
  • fungal infection
  • immunosuppression
  • infants
  • lactase deficiency
  • neonates
  • pregnancy
  • premature neonates


  • Amphotericin B
  • Anidulafungin
  • Antifungals
  • Fluconazole
  • Flucytosine
  • Griseofulvin
  • Itraconazole
  • Ketoconazole
  • Micafungin
  • Posaconazole
  • Terbinafine
  • Voriconazole

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