More Selective Antibiotic Shows Promise for C difficile Infection

Brandon May

May 06, 2022

An investigational, novel oral antibiotic with greater selectivity than vancomycin, metronidazole, and even fidaxomicin may offer improved protection of healthy gut bacteria during the treatment of Clostridium difficile infection (CDI), according to ongoing research.

"CDI treatment has historically been dominated by metronidazole and vancomycin," said Katherine Johnson, DO, from the Western Infectious Disease Consultants, PC, in Denver, Colorado. However, these broad-spectrum drugs negatively affect healthy bacteria in the gut and increase the risk of CDI recurrence.

This is also a problem for drugs in the CDI antibiotic pipeline; many candidate drugs have failed because of their broad-spectrum activity, she added during a session at the Peggy Lillis Foundation 2022 National C diff Advocacy Summit.

"An ideal CDI therapy would be a very narrow-spectrum antibiotic that has a minimal effect on normal gut bacteria," she said.

Johnson is currently working on a phase 2 clinical trial that is evaluating the novel antibiotic, dubbed CRS3123, for the treatment of primary CDI and first-recurrence CDI. The investigational agent targets and inhibits a form of the methionyl tRNA synthetase enzyme, which is strictly required for protein biosynthesis in C difficile and is therefore an ideal target for treatment of primary and recurrent CDI.

In her session, Johnson reported that CRS3123 inhibits the damaging toxins produced by C difficile, potentially resulting in more rapid symptom resolution. Additionally, owing to its novel mode of action, no strains are currently resistant to CRS3123.

She presented findings from an animal study that showed that CRS3123 was superior to vancomycin in terms of prolonging survival. She also presented findings from phase 1 clinical trials that showed that most adverse events (AEs) associated with CRS3123 were mild. No serious AEs were reported.

A "Huge Infectious Burden"

If successful in further research, CRS3123 could offer significant value to patients with C difficile, especially those with recurrent infection, given the sometimes extreme clinical, quality-of-life, and economic burdens associated with CDI.

Dr Byron Vaughn

"CDI is a huge infectious burden to the US healthcare system and globally has been listed by the Centers for Disease Control and Prevention as an urgent threat," Byron Vaughn, MD, from the University of Minnesota, told Medscape Medical News.

"Despite a number of antibiotic stewardship and infection control and prevention efforts, we haven't seen much of a change in the incidence of CDI," he said. He said that the risk of recurrence can be as high as 30%.

While oral vancomycin is effective for treating C difficile, Vaughn noted that the antibiotic lacks selectivity and destroys healthy gut bacteria, resulting in substantial dysbiosis. "Dysbiosis is really the key to getting recurrent C difficile," he explained, "because if you have healthy gut bacteria, you will inherently resist CDI."

Vaughn stated that his center is in the startup phase for being a site for a clinical trial of CRS3123. The hope is that CRS3123, because its spectrum is narrower than that of fidaxomicin and vancomycin, doesn't induce intestinal dysbiosis. "It really just treats the C difficile and leaves every other bug alone so that your gut bacteria can recover while the C difficile is being treated," he said. "And then when you stop CRS3123, you have healthy gut bacteria already present to prevent recurrence."

If this is confirmed in large-scale trials, there could be a "dramatic decrease" in the rates of recurrent C difficile, said Vaughn.

Aside from the potential clinical impact, the economic implications of a novel selective antibiotic that preserves healthy gut bacteria could be significant, he added. "Depending on exactly what population you're looking at, probably about a third of the cost of C difficile is actually attributable to recurrence. That's a huge economic burden that could be improved."

Johnson is an employee of Crestone, which is developing CRS3123. Vaughn reports no relevant financial relationships.

Peggy Lillis Foundation 2022 National C. diff Advocacy Summit: Presented May 2, 2022.

Brandon May is a freelance medical journalist who has written more than 900 articles for medical publications in the United States and the United Kingdom. He resides in downtown Brooklyn, New York City. Twitter: @brandonmilesmay.

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