Background: Despite advancements, recurrent Clostridium difficile infections (CDI) remain an urgent public health threat with insufficient response rates to currently approved antibiotic therapies. Microbiota-based treatments appear effective, but rigorous clinical trials are required to optimize dosing strategies and substantiate long-term safety.
Methods: This randomized, double-blind, placebo-controlled phase 2B trial enrolled adults with 2 or more CDI recurrences to receive: 2 doses of RBX2660, a standardized microbiota-based drug (group A); 2doses of placebo (group B); or 1 dose of RBX2660 followed by 1 dose of placebo (group C). Efficacy was defined as prevention of recurrent CDI for 8 weeks following treatment. Participants who had a recurrence within 8 weeks were eligible to receive up to 2 open-label RBX2660 doses. The primary endpoint was efficacy for group A compared to group B. Secondary endpoints included the efficacy of group C compared to group B, combined efficacy in the blinded and open-label phases, and safety for 24 months.
Results: The efficacy for groups A, B, and C were 61%, 45%, and 67%, respectively. The primary endpoint was not met (P = .152). One RBX2660 dose (group C) was superior to placebo (group B; P = .048), and the overall efficacy (including open-label response) for RBX2660-treated participants was 88.8%. Adverse events did not differ significantly among treatment groups.
Conclusions: One, but not 2, doses of RBX2660 was superior to placebo in this randomized, placebo-controlled trial. These data provide important insights for a larger phase 3 trial and continued clinical development of RBX2660.
Clinical trials registration: NCT02299570.