FDA Clears Immuron’s IMM-529 For Clinical Testing in C difficile; Phase 2 Set to Begin in Australia

The FDA approved Immuron Limited’s investigational new drug application for IMM-529 (IND 032095), authorizing a phase 2 clinical trial in adults with Clostridioides difficile infection. Immuron plans to start the study in the first half of 2026. The multicenter Australian trial will enroll up to 60 participants with a first episode or recurrent disease in a randomized, double-blind, placebo-controlled design, allocating patients 2:1 to IMM-529 plus standard of care or placebo plus standard of care. The primary objective is safety and tolerability. Efficacy assessments will include mortality, disease symptoms, and recurrence rates.¹

IMM-529 is an orally delivered, bovine colostrum–derived polyclonal antibody product that targets 3 C difficile virulence components: toxin B, spores, and surface-layer proteins of vegetative cells. In preclinical infection and relapse models, antibodies generated for IMM-529 were associated with prevention of primary disease of 80% (P = .0052), protection from recurrence of 67% (P < .01), and treatment of primary disease of 78.6% (P < .0001, toxin B–focused hyperimmune bovine colostrum). Cross-reactivity has been reported against multiple human strains, including hypervirulent lineages. The product is being developed as an adjunct to antibiotic standard of care to aid clearance of infection and support re-establishment of the gut microbiota.¹

October 31, 2025: Before IND clearance, Immuron reported that the FDA had the IMM-529 IND under active review and requested additional clinical information. The company submitted a comprehensive reply and minor protocol updates ahead of the 30-day decision date. Immuron also stated that topline data from the USU phase 2 Travelan study in long-term traveler and deployed populations (n = 851; powdered IMM-124E/Travelan 600 mg twice daily vs placebo) were delayed to the end of November 2025 because of the US government shutdown. The company plans to use these results to select dosing for an end-of-phase 2 meeting with the FDA.²

If outcomes are favorable, Immuron intends to propose a twice-daily regimen. If not superior to prior data supporting three-times-daily dosing for the commercial tablet, the company would consider retaining three-times-daily dosing.²

Selected Travelan findings from prior double-blind, placebo-controlled enterotoxigenic Escherichia coli human challenge studies:²

• 200 to 400 mg three times daily (n = 60; attack rate 86%): 58% to 83% protection against diarrhea and 54% to 87% reduction in loose stools, with symptom reductions.
• 400 mg three times daily (n = 30; attack rate 73%): 90.5% protection against diarrhea and 91% reduction in loose stools, with 100% reduction in abdominal pain and faster clearance of the challenge strain.
• 1,200 mg once daily (n = 60; overall attack rate 37%; cohort 1 attack rate 54%): 37% to 57% protection, 29% reduction in loose stools, broader symptom reductions, and faster pathogen clearance.

The USU field study uses a powdered formulation and twice-daily dosing that differ from directions for the commercial tablet product. Travelan is listed in Australia and licensed in Canada for risk reduction of travelers’ diarrhea and is sold in the United States as a dietary supplement.¹

C difficile remains the most common pathogen in healthcare-associated infections in the United States and was categorized as an urgent antimicrobial resistance threat by the Centers for Disease Control and Prevention in 2019. Each year, more than 400,000 people in the United States are affected and more than 30,000 deaths are attributed. Recurrent infection is common after antibiotic exposure because of disruption of the intestinal microbiota.1

Overall, Immuron cites opportunity analysis suggesting IMM-529 could be positioned early in the treatment algorithm as payers allow; if used at first recurrence, an estimated 98,000 US patients could be eligible. As both programs remain investigational in the United States, practice implications will depend on phase 2 safety and efficacy signals and subsequent regulatory feedback.

References

1.Immuron. Immuron IMM-529 IND approved by FDA. November 5, 2025. Biospace. Accessed November 5, 2025. https://www.biospace.com/press-releases/immuron-imm-529-ind-approved-by-fda

2.Immuron. Immuron Announces Clinical Trial Update. Glovenewswire. October 31, 2025. Accessed November 5, 2025. https://www.globenewswire.com/news-release/2025/10/31/3178196/0/en/Immuron-Announces-Clinical-Trial-Update.html