Profile 1: Recurrent Clostridioides difficile Infection (rCDI)
For recurrent C. difficile infection, FMT is the best-proven option: it rebuilds colonization resistance, and the diarrhea often clears within days.
| Parameter | rCDI-specific detail |
|---|---|
| Evidence level | ★★★★★ Very strong. Multiple independent RCTs; standard of care in many countries. Cure rates 81–94% by colonoscopic FMT vs. 31% for vancomycin. |
| Mechanism of dysbiosis | Antibiotic-induced elimination of colonization resistance. C. difficile occupies vacated niches; toxin A/B production drives colitis cycle. |
| Primary microbiota targets | Restore Lachnospiraceae, Ruminococcaceae, Bacteroidetes. Suppress C. difficile via ecological competition, not antibiotic pressure. |
| Protocol modification | No compatibility assessment phase (Phase 0) required. Begin directly at Phase 1 induction — urgency justifies immediate high-dose delivery. Colonoscopic route preferred for first FMT. |
| Minimum transfer duration | 30 days from induction start. Shorter than non-CDI indications; ecological displacement of C. difficile can be achieved more rapidly than chronic remodeling. |
| Priority exposome focus | Strict antibiotic avoidance post-FMT. Dietary fiber (target ≥25 g/day) to maintain colonization resistance. Minimize PPI use if possible. |
| Expected response timeline | Diarrhea resolution typically within 3–7 days of induction. If no improvement by day 7, notify clinical team same day. |
| Warning signs (rCDI-specific) | Persistent diarrhea > 7 days post-FMT. Fever >38.5°C. Blood in stool. Abdominal rigidity (possible toxic megacolon — emergency referral). |
Table 12 – Clinical profile: Recurrent C. difficile infection (rCDI) # Protocol parameters, evidence level, and clinical modifications specific to the rCDI indication.
In 2022–2023, two live biotherapeutic products[G] (LBPs) received FDA approval for the prevention of recurrent C. difficile infection (rCDI) in adults following antibacterial treatment for rCDI. These are the first and to date only microbiome-targeted drugs with formal regulatory authorization; they fundamentally reshape the rCDI treatment decision algorithm.
Rebyota (RBX2660) — Ferring, Nov 30, 2022
A single-dose, rectally administered full human microbiota suspension[G]. The PUNCH CD3 pivotal trial (Khanna et al. 2022) demonstrated 70.6% sustained success (rCDI-free through week 8) vs. 57.5% placebo (NNT ≈ 8) [401], [404]. Administration: 24–72 hours after completion of CDI-targeted antibiotic (vancomycin or fidaxomicin), in an outpatient setting.
Vowst (SER-109) — Seres Therapeutics, April 26, 2023
A purified Firmicutes spore oral capsule[G] (4 capsules once daily for 3 days). The ECOSPOR III pivotal trial (Feuerstadt et al. 2022, NEJM) showed 12% rCDI recurrence vs. 40% placebo at week 8 — NNT ≈ 4 [402], [405]. Oral dosing makes it outpatient-friendly, without need for colonoscopy or rectal administration.
VE303 (Vedanta) — Phase 3 Ongoing
A defined 8-strain Clostridia consortium representing a fully synthetic, strain-level characterized formulation, in contrast to donor-derived products. Phase 2 (Louie et al. 2023, JAMA): 13.8% recurrence vs. 45.5% placebo [403]. The RESTORATiVE303 phase 3 trial is expected to complete in 2025.
Clinical Choice Algorithm
| Situation | Preferred option |
|---|---|
| Second rCDI episode (3rd infection overall), outpatient | Vowst (oral, outpatient-friendly) or conventional capsule-based FMT |
| Severely ill, immunocompromised, colonoscopy contraindicated | Rebyota (rectal) or conventional retention enema FMT |
| Complex rCDI (≥3 recurrences), non-CDI comorbid indication suspected | Conventional donor FMT (compatibility-matched, colonoscopic) |
| Under clinical trial protocol, non-rCDI indication | Conventional donor FMT (only within trial frameworks) |
LBPs do not replace conventional FMT for non-CDI indications — for IBD, IBS, metabolic, and neuropsychiatric indications, donor-derived FMT performed under clinical-trial protocol remains the standard.
References
[401] Khanna S, Assi M, Lee C et al. Efficacy and Safety of RBX2660 in PUNCH CD3, a Phase III, Randomized, Double-Blind, Placebo-Controlled Trial. Drugs. 2022. Link
This phase III randomized, double-blind, placebo-controlled trial evaluated RBX2660, a live biotherapeutic prepared from human stool, for reducing recurrent C. difficile infection. A Bayesian primary analysis integrated phase III with prior phase IIb data. Adults with ≥1 prior CDI recurrence and standard-of-care antibiotic treatment were randomized 2:1 to a single enema of RBX2660 or placebo. The primary endpoint was treatment success — absence of CDI diarrhea within 8 weeks. Of 320 screened, 289 were randomized and 267 received blinded treatment (RBX2660 n=180; placebo n=87). RBX2660 demonstrated significant superiority over placebo in achieving sustained clinical response, with an acceptable safety profile. The findings supported regulatory approval of RBX2660 (Rebyota) as a microbiome-based therapy for recurrent CDI.
[402] Feuerstadt P, Louie TJ, Lashner B et al. SER-109, an Oral Microbiome Therapy for Recurrent Clostridioides difficile Infection. New England Journal of Medicine. 2022. Link
This phase III RCT (ECOSPOR III) tested SER-109, an oral microbiome therapeutic of purified Firmicutes spores, in adults with ≥3 CDI episodes (inclusive of the qualifying acute episode). After standard-of-care antibiotics, patients received SER-109 or placebo (4 capsules daily for 3 days). Diagnosis required toxin testing at trial entry, with stratification by age and antibiotic. The primary efficacy endpoint was reduced risk of CDI recurrence at 8 weeks. SER-109 achieved significant superiority over placebo for sustained clinical response. Analyses also documented microbiome engraftment and shifts in microbial metabolites consistent with the spore-formulation mechanism. The trial supported FDA approval of SER-109 (Vowst) as the first oral microbiome therapeutic for recurrent CDI.
[403] Louie T, Golan Y, Khanna S et al. VE303, a Defined Bacterial Consortium, for Prevention of Recurrent Clostridioides difficile Infection: A Randomized Clinical Trial. JAMA. 2023. Link
This phase 2 dose-ranging RCT (CONSORTIUM) evaluated VE303, a defined 8-strain commensal Clostridia consortium, in adults at high risk of CDI recurrence (n=79; ≥1 prior CDI in last 6 months, or primary CDI at high risk by age ≥75, or ≥65 with risk factors). Patients were randomized to high-dose VE303 (8.0×10^9 CFU; n=30), low-dose VE303 (1.6×10^9 CFU; n=27), or placebo (n=22) once daily orally for 14 days after standard-of-care antibiotics. The primary objective was to identify the phase 3 dose. High-dose VE303 reduced CDI recurrence relative to placebo and outperformed the low-dose arm, supporting the higher dose for phase 3. The trial provided proof-of-concept for rationally defined non-toxigenic Clostridia consortia as recurrent-CDI prevention.
[404] . FDA Approves First Fecal Microbiota Product (Rebyota). . 2022. Link
FDA news release: on 30 November 2022 the U.S. FDA approved Rebyota (fecal microbiota, live-jslm; formerly RBX2660, Ferring/Rebiotix) — the first approved fecal microbiota product — for prevention of recurrent Clostridioides difficile infection (CDI) in adults (>=18 years) after completion of antibiotic treatment for recurrent CDI. It is administered rectally as a single dose.
[405] . FDA Approves First Orally Administered Fecal Microbiota Product (Vowst). . 2023. Link
FDA news release: in April 2023 the U.S. FDA approved Vowst (fecal microbiota spores, live-brpk; formerly SER-109, Seres Therapeutics) — the first orally administered fecal microbiota product — for prevention of recurrent CDI in adults after antibiotic treatment for recurrent CDI. Unlike rectally delivered Rebyota, Vowst is taken as oral capsules of purified bacterial spores.