Summit Therapeutics Shares New Data – Phase 2 Clinical Trial of ridinilazole for C. difficile infection (CDI)

Summit Therapeutics Reports New Data from Phase 2 Clinical Trial Connecting Ridinilazole’s Microbiome Preservation to Improved Clinical Outcomes for Patients with C. difficile Infection

October 2019

Summit Therapeutics announced the presentation of new data that explain the link between two key findings in the Company’s Phase 2 clinical trial of ridinilazole for C. difficile infection (‘CDI’):

  • Ridinilazole demonstrated superior efficacy compared to vancomycin, driven by a 60% lower recurrence rate.
  • Ridinilazole preserved the diversity of the gut microbiome.

Researchers at Tufts University, collaborating with Summit, showed that these findings are connected mechanistically by bile acids, part of the ‘metabolome’ of active chemicals made or modified by gut bacteria. Bile acids exist in different forms that can either favour or block the regrowth of C. difficile after treatment. Vancomycin kills bacteria that turn pro-C. difficile bile acids into anti-C. difficile bile acids – leaving an adverse ratio of pro- and anti-growth chemicals that favours the regrowth of C. difficile and the recurrence of C. difficile infection. By contrast, ridinilazole leaves these bacteria unharmed, allowing them to keep converting pro-C. difficile bile acids into anti-C. difficile bile acids, maintaining a positive chemical balance that prevents C. difficile recurrence.

“The damaging effect of broad-spectrum antibiotics in the treatment of CDI is far-reaching from the make-up and function of the gut microbiome through the poor clinical outcomes seen in one third of patients, driven by a high rate of disease recurrence,” said Dr David Roblin, President of R&D of Summit. “Ridinilazole has the potential to be a targeted CDI treatment that could result in significantly better patient outcomes for the over half million US patients per year who have an episode of CDI. These latest data help to put the science behind the function of a healthy microbiome into context and highlight its importance in sustaining CDI cures.”

The Phase 2 clinical trial enrolled 100 patients, half of whom received ridinilazole and the other half vancomycin. For both groups, there was a higher ratio of pro-C. difficile to anti C.-difficile bile acids at the start of treatment. This was expected, as patients who get CDI have perturbed microbiomes. However, during treatment, the proportion of anti-C. difficile bile acids increased in patients treated with ridinilazole, whereas patients treated with vancomycin initially showed decreases in anti-C. difficile bile acids and had stools dominated by pro-C. difficile bile acids. By the end of treatment, ridinilazole-treated patients’ bile acid ratios returned towards a healthy, non-CDI state. These results support the data from the Phase 2 clinical trial, in which patients receiving ridinilazole showed a statistically significant improvement in sustained clinical responses.

Copies of the two poster presentations are available in the Publications section of Summit’s website, www.summitplc.com.

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