What is Vowst?

Vowst is an orally administered FDA-approved, preventive medication that may be given to people who have had an infection with Clostridioides difficile (also called Clostridium difficile) bacteria before, to prevent it from happening again following a standard course of C. difficile antibiotic treatment. Vowst is not a treatment for C. difficile infection (CDI).

Vowst was approved for the prevention of recurrence of C. difficile infection on April 26, 2023.

What does Vowst contain?

The active ingredient in Vowst is a mixture of live gut bacteria that has been extracted from highly purified fecal matter that has been donated by healthy volunteers. The gut bacteria contained is a consortium of Firmicutes spores, which normally live in a healthy microbiome. The active ingredient of Vowst is described as fecal microbiota spores, live-brpk (formerly called SER-109).

What is the dosage of Vowst?

The adult dosage of Vowst is four capsules as a single dose for three consecutive days. Each capsule contains 3 × 10⁷ spore colony–forming units. The first dose should be administered within 4 days of the completion of C.difficile antibiotic treatment.

In clinical trials, patients took 10 oz of magnesium citrate 1 day prior to treatment with Vowst to ensure any remaining antibiotic was washed out.

Who makes Vowst?

Vowst is made by Seres Therapeutics in collaboration with Nestlé Health Science.

When is Vowst expected to be available?

Vowst is expected to be available sometime in June 2023.

What is Clostridioides difficile (C. difficile) infection?

Broad-spectrum antibiotics treat a wide range of bacterial infections such as endocarditis (a heart infection), osteomyelitis (a bone infection), gut, and skin infections, and they can be life-saving. But one of the main problems with broad-spectrum antibiotics is that they disrupt the gut microbiota – this is the collection of bacteria, archaea, and eukarya that colonize the gastrointestinal tract which research has shown have a profound influence on our health.

How much an antibiotic affects the microbiota depends on its class, how it works, the degree of bacterial resistance to the antibiotic used, the dosage, the route, and what particular bacteria it targets. Clostridioides difficile (also known as Clostridium difficile) is a bacteria that is present in soil, water, and air, that is usually harmless. But it is opportunistic and can take advantage of a microbiota that has been compromised by antibiotics or a person whose immune system is not functioning well. When given room to grow it can quickly multiply, taking over any remaining beneficial bacteria in the gut and removing the primary defense against potential pathogens. Once the infection is established, C. difficile bacteria release toxins that inflame the lining of the gut and can cause severe diarrhea (which can be life-threatening), fever, and abdominal pain.

Prior exposure to broad-spectrum antibiotics in the last month increases the risk of developing C. difficile infection seven to ten-fold. Other people at high risk include older adults, those who are immunocompromised, or with cancer, renal impairment, or previous proton pump inhibitor use.

Why is Vowst only used for recurrent CDI?

The gut microbiota in most patients who have had a prior episode of C. difficile infection is resilient enough to recover and these patients will not experience another CDI episode. However, some people experience persistent microbiota disruption, and once they have completed the CDI-targeted antibiotic treatment (which is usually vancomycin or fidaxomicin) experience further episodes of CDI due to spore germination and multiplication of C. difficile bacteria. The cycle repeats easily because bile acid pathways favor C. difficile bacteria once defensive bacteria are depleted by antibiotics.

How does Vowst work?

Vowst contains a consortium of Firmicutes spores (Firmicutes are a dominant type of bacteria that live within our gut microbiota). The spores in Vowst are highly resistant to destruction and metabolically dormant. After they are orally ingested, the spores germinate in response to intestinal bile acids in the intestine and colon, recolonizing the gut microbiota, and relieving symptoms of C. difficile infection.

What are the side effects of Vowst?

Vowst is well tolerated and the main side effects were gastrointestinal tract upset (such as diarrhea, flatulence, nausea, abdominal pain, and bloating), urinary tract infections (UTIs), and fatigue. One person with a history of allergic reactions to other medications experienced mild facial flushing, fever, and moderate throat and jaw tightness.

How effective is Vowst?

A phase-3 open-label trial that investigated the use of Vowst (known then as SER-109) found consistently low rates for CDI recurrence. 8.7% had a CDI recurrence by week 8, and 13.7% had a recurrence by week 24. Sustained clinical response rates were 91.3%.

The authors concluded that early treatment with SER-109 at the time of first recurrence may be associated with reduced morbidity from recurrent CDI.