Safety and Tolerability of CP101, a Full-Spectrum, Oral Microbiome Therapeutic for the Prevention of Recurrent Clostridioides difficile Infection: A Phase 2 Randomized Controlled Trial

Background & Aims: Recurrent Clostridioides difficile infections (CDIs) remain common. While novel microbiome therapeutics gain approval, the efficacy of a full-spectrum, oral microbiome therapeutic is unknown. This study aimed to determine the safety and efficacy of CP101, an orally administered microbiome therapeutic, to restore a diverse microbiome and prevent recurrent CDI in a broad population. Methods: We conducted a multicenter, phase 2, double-blind, randomized, placebo-controlled trial in adults with recurrent CDI. Participants with one or more CDI recurrences and diagnosis by polymerase chain reaction or toxin enzyme immunoassay for the qualifying episode were included. Participants were randomized 1:1 to receive a single oral dose of either CP101 (∼6 × 1011 colony-forming units of lyophilized microbial cells) or placebo after standard-of-care antibiotics. The primary efficacy endpoint was the proportion of participants without CDI recurrence through week 8. Safety, efficacy, and microbiome endpoints were evaluated through weeks 8 and 24. Results: A total of 198 participants were analyzed: CP101 (n = 102) and placebo (n = 96). Overall, 27.5% had a first recurrence, and 62.7% were diagnosed by polymerase chain reaction–based testing. The proportion without CDI recurrence through week 8 was significantly higher in the CP101 group compared to the placebo group (74.5% [76 of 102] vs 61.5% [59 of 96], respectively; P = .0488), with durable efficacy observed through week 24 (73.5% [75 of 102] vs 59.4% [57 of 96], respectively; P = .0347). Similar efficacy was observed regardless of diagnostic modality or number of CDI recurrences. Rapid and durable increase in microbiome diversity was observed in the CP101 group compared to the placebo group. The incidence of adverse events was similar between the 2 groups. Conclusions: CP101 was superior to placebo in reducing recurrent CDI with a safety profile similar to placebo. (ClinicalTrials.gov, Number NCT03110133) © 2025 AGA Institute