Summit makes case for changes to antibiotic R&D after sharing data from failed phase 3 trial

Ten months after revealing a phase 3 flop, Summit Therapeutics has shared data from an antibiotic trial and framed it as evidence of a potential need to change how anti-infectives are developed and assessed. 

In December, Summit reported that its targeted-spectrum antimicrobial ridinilazole performed no better than the approved vancomycin in terms of the clinical response rate in Clostridioides difficile infection. The biotech spoke to the FDA over the summer, leaving the meeting with the impression that a path to market is still open for ridinilazole—if it runs at least one more clinical trial.

Summit used the infectious disease event IDWeek 2022 to present data from the failed Ri-CoDIFy phase 3 study. The sustained clinical response rate in the ridinilazole arm came in at 73% compared to 70.7% in the vancomycin active control cohort. The small numerical difference fell short of the level needed to show ridinilazole is superior to vancomycin.

While the lack of impact on response rates caused the study to miss its primary endpoint, Summit made the case that ridinilazole has an edge in other regards, notably in terms of the rate of recurrence. The recurrence rate in the ridinilazole arm was 8.1% versus 17.3% in the vancomycin cohort. Summit framed the difference as a result of the effects of the two molecules on the microbiome. 

The biotech found ridinilazole had minimal impact on gut microbiome diversity compared to vancomycin and is less likely to promote resistance to antibiotics. Summit thinks such factors should be factored into assessments of the merits of antibiotics.

“We believe that this study may be indicative as to the need to change the way in which anti-infective agents are developed and assessed going forward, including the need for monitoring the impact of treatments on the gut microbiome,” Summit CEO Robert Duggan said in a release. “A diverse microbiome is critical to human health and protecting it must be a focus going forward.” 

Summit’s statement provides no update on its plans for ridinilazole. The company said it planned to explore the possibility of running further studies to support approval after getting feedback from the FDA earlier in the year.