Abstract VOWST (VOWST oral spores, VOS; fecal microbiota spores, live-brpk, formerly SER-109) is an FDA-approved, orally administered consortium of purified Firmicutes spores developed to prevent recurrent Clostridioides difficile infection (CDI). Although 86.7% (26/30) of patients with recurrent CDI did not experience a subsequent recurrence over 8 weeks in an open-label phase 1b study, a subsequent double-blind phase 2 study ( NCT02437487 ) did not demonstrate a significant benefit over placebo (rate of recurrence at 8 weeks in SER-109 versus placebo: 44.1% versus 53.3%). These discordant outcomes were hypothesized to be due to suboptimal dosing. This hypothesis was addressed in a pivotal phase 3 trial ( NCT03183128 ) using an approximately tenfold higher dose. In phase 3, only 12% of VOS-treated patients versus 40% of placebo patients recurred by week 8 (relative risk 0.32, P < 0.001). Here in this follow-up post hoc analysis, across-trial comparisons confirmed that the higher, efficacious phase 3 dose is associated with improved pharmacokinetics, assessed by VOS engraftment (patients with available samples: phase 1b: 28, phase 2: 79, phase 3: 170). In-depth phase 3 analyses revealed that VOS significantly altered microbial composition, significantly enriching the diversity and abundance of Firmicutes species and reducing the prevalence and abundance of C. difficile and opportunistic pathogens (for example, Enterobacteriaceae species). Consistent with these taxonomic changes, significant changes in key bioactive metabolites were observed, including depletion of conjugated and deconjugated primary bile acids, enrichment of secondary bile acids and increases in short-chain and medium-chain fatty acids. In vitro, VOS batches produced these C. difficile -inhibiting metabolites. These findings on the pharmacology of VOS underscore the importance of rapidly restoring key protective functions of the microbiome in patients with recurrent CDI to achieve durable prevention of recurrence, as observed in the phase 3 study; they also highlight the need to include the microbiome in the clinical management of CDI. ClinicalTrials.gov registrations: NCT02437487 and NCT03183128 .
Bryant et al. (Mon,) studied this question.