FMT in a Pill: FDA OKs Second Product to Prevent C difficile Recurrence

Jennie Smith

April 28, 2023

The recent approval of the first oral fecal-derived microbiota therapy to prevent the recurrence of Clostridioides difficile (C. diff) infection in patients was welcome news for physicians who've struggled under the weight of having too few treatment options for the prevention of C. diff recurrence.

The product, developed by Massachusetts-based Seres Therapeutics and marketed as Vowst, was approved by the U.S. Food and Drug Administration on April 26. It is approved for use in adults who have already been treated with antibiotics for a recurrent infection with C. diff bacteria.

This is the first oral treatment for the prevention of C. diff recurrence and is designed to be delivered in four capsules taken daily for 3 days.

Vowst is the second therapy derived from human stool to be approved for the indication in less than 6 months. In December, the FDA approved Rebyota (Ferring), a rectally delivered treatment that also uses microbes from donor feces. Both products were given priority review, orphan drug, and breakthrough therapy designations by the agency.

C. diff infection can be aggravated by an alteration of normal gut flora associated with antibiotics treatment, leading to cycles of repeated infections. Infection can produce diarrhea, abdominal pain, fever, and severe morbidity. In the United States, an estimated 15,000 to 30,000 deaths per year are linked to C. diff. Risk factors for recurrent infection include being 65 or older, hospitalization, being in a nursing home, a weakened immune system, and previous infection with C. diff.

Therapies transplanting fecal microbiota from donors have been used since the 1950s as treatments for recurrent C. diff infection, and in the past decade, as stool banks recruiting screened donors have made fecal microbiota transplants, or FMT, standard of care. However, only in recent years have fecal-derived therapies become subject to standardized safety and efficacy testing.

Both the current FDA-approved products, Rebyota and Vowst, were shown in randomized controlled trials to reduce recurrence of C. diff infection, compared with placebo. In a phase 3 clinical trial of Rebyota (n = 262) in antibiotic-treated patients, one rectally administered dose reduced recurrence of C. diff infection by 70.6% at 8 weeks, compared with 57.5% for placebo. A phase 3 study of Vowst (n = 281) showed recurrence in treated subjects to be 12.4% at 8 weeks, compared with nearly 40% of those receiving placebo (relative risk, 0.32; 95% confidence interval, 0.18-0.58; P less than .001).

Despite screening protocols that have become increasingly homogenized and rigorous, FMT is associated with the risk of introducing pathogens. Vowst is manufactured with purified bacterial spores derived from donor feces, not whole stool. Nonetheless, FDA noted in its statement that Vowst could still potentially introduce infectious agents or allergens.

Antibiotics Are Still First-Line Treatment

In an interview, Jessica Allegretti, MD, MPH, AGAF, medical director of the Crohn's and Colitis Center at Brigham & Women's Hospital, Boston, said that having two FDA-approved therapies with different means of administration "is great for the field and great for patients. These are both meant to be used after a course of antibiotics, so antibiotics are still the mainstay of treatment for C. diff and recurrent C. diff, but we now have more options to prevent recurrence."

The convenience of an oral therapy that can be taken at home is "very attractive," Allegretti added, noting that there will also be patients "who either don't want to or can't take capsules, for whom a rectal administration [in a health care setting] may be preferred."

Allegretti, who has used FMT to treat recurrent C. difficile for more than a decade, said that she expected traditional FMT using screened donor stool to remain available even as the new products are adopted by clinicians. FMT centers like OpenBiome "will continue to provide access for patients who either don't have the ability to get the FDA-approved products because of insurance coverage, or for financial reasons, or maybe neither of the new products is appropriate for them," she said. "I do think there will always be a need for the traditional option. The more options that we have available the better."

TD Cowen analyst Joseph Thome told Reuters that the drug could be priced close to $20,000 per course, expecting peak sales of $750 million in the U.S. in 2033.

Allegretti disclosed consulting work for Seres Therapeutics, Ferring, and other manufacturers. She is a member of OpenBiome's clinical advisory board.

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