From Stool Transplant to Approved Product: Microbiome Therapy Evidence in Recurrent C. diff

Recurrent Clostridioides difficile infection now has two FDA-approved microbiome medicines, and both trace directly back to fecal microbiota transplantation (FMT). Rebyota (fecal microbiota, live-jslm), approved in November 2022, and Vowst (fecal microbiota spores, live-brpk), approved in April 2023, are the first standardized, regulated versions of what clinicians once delivered as raw donor stool, per the FDA product pages for each. Both are approved to prevent recurrence after a patient completes antibiotics, not to treat an active infection. Reading their trial results correctly means looking at the gap between drug and placebo, not the headline success rate on its own.

From donor stool to a regulated biologic

Recurrent CDI is a disease of a damaged ecosystem. Repeated antibiotic courses that knock down C. difficile also flatten the surrounding gut community, and that loss of diversity is what lets the organism keep coming back. The logic of FMT was to repair the ecosystem rather than keep attacking one bug: transfer screened stool from a healthy donor into the patient and let a normal microbial community re-establish.

For years that was done as an investigational procedure, not an approved medicine. Case series and small randomized trials reported high resolution rates for recurrent CDI, often cited around 80 to 90 percent, and the review in the cited PMC article traces how those results built the biological case for microbiome restoration. The problem was standardization and safety. Donor stool is variable from batch to batch, screening practices differed between centers, and the FDA has documented transmission of drug-resistant organisms through investigational FMT, including serious outcomes. Regulators classified stool used this way as a biologic and allowed its use for recurrent CDI not responding to standard therapy under enforcement discretion, an interim posture rather than a stamp of approval.

The two approved products are what happens when that practice is turned into a manufactured drug: defined donor screening, controlled processing, characterized composition, and lot release testing. That is the real shift from stool transplant to approved product.

What the two products are

Rebyota

Rebyota is a single-dose microbiota suspension delivered rectally, indicated for the prevention of recurrence of CDI in people 18 and older following antibiotic treatment for recurrent CDI, according to the FDA. It is a broad consortium product, a full microbial community prepared from screened human stool. Its pivotal evidence came from the PUNCH CD3 program, a randomized, double-blind, placebo-controlled trial. In the primary analysis, modeled treatment success (no CDI recurrence at eight weeks) was about 70.6 percent with Rebyota versus 57.5 percent with placebo, as summarized in the cited review.

Vowst

Vowst is an oral capsule, the first fecal microbiota product taken by mouth, indicated for the same prevention-of-recurrence setting in adults after antibacterial treatment, per the FDA. Rather than a whole-community transplant, it is a purified preparation of bacterial spores (Firmicutes) that survive processing and the passage through the stomach. Its pivotal trial, ECOSPOR III, was published in the New England Journal of Medicine. Recurrence at eight weeks was 12 percent with the product versus 40 percent with placebo, a relative risk of roughly 0.32. Put the other way, about 88 percent of the treatment group stayed recurrence-free at eight weeks versus about 60 percent on placebo, and the separation held at six months.

How to read the success rates

The most common misread is to line up 70.6 percent against 88 percent and conclude one product is far stronger. That comparison is not valid, for several reasons.

First, the placebo arms were not untreated. Everyone in these trials had already received standard-of-care antibiotics (vancomycin or fidaxomicin) for their recurrence before randomization. A meaningful fraction would stay well on antibiotics alone, which is exactly why the placebo groups did so well (57.5 percent and 60 percent). The honest measure of what the microbiome product adds is the absolute difference over placebo, roughly 13 percentage points for Rebyota and roughly 28 for Vowst within their own trials. That within-trial delta is the signal; the raw single-arm number is not.

Second, the trials used different endpoints and definitions. Rebyota's headline figure is a modeled treatment-success estimate; Vowst's is an observed recurrence rate. Enrollment criteria differed in how many prior episodes were required, and the way recurrence is confirmed matters enormously. A toxin-based test and a PCR test disagree about who is truly infected versus merely colonized, and that choice shifts recurrence counts in both arms. When placebo response differs between two trials (57.5 versus 40 percent), that alone tells you the populations and definitions were not the same.

Third, route and product design differ. A rectal whole-community suspension and an oral purified-spore capsule are different interventions, and patient preference, access, and adherence all sit outside the efficacy number.

The disciplined takeaway is that both products beat an already-treated placebo in adequate, well-controlled trials, which is what earned approval. Cross-trial rankings of the two are marketing, not evidence.

Where the evidence still has edges

These approvals cover a specific job: preventing the next recurrence after antibiotics have controlled the current episode. They are not treatments for a first infection, not treatments for active severe CDI, and not general gut-health products. Long-term follow-up is still accumulating, the trials studied adults, and durability beyond the reported windows remains an area of ongoing study. Investigational donor FMT also continues to exist alongside the approved products under the FDA's enforcement-discretion posture for eligible patients, which is a regulatory status rather than a claim of equivalence.

This article is educational and is not medical advice; decisions about recurrent CDI belong with a qualified clinician who knows the specific case.