Rima Rachid, MD, from Boston Children’s Hospital.

Rima Rachid, MD

Antibiotic pretreatment before oral fecal microbiota transplantation (FMT) raised the peanut allergy response rate to 60% compared with 30% without pretreatment in a phase 1 trial of adults with severe 

Omalizumab is now the only FDA-approved option for peanut allergy, following the discontinuation of Palforzia oral immunotherapy on July 31, 2026, and even it lacks evidence of durable disease modification once therapy stops.

Investigators at Boston Children's Hospital tested FMT from healthy, non-allergic donors as a potential alternative in this phase 1 open-label trial.

Antibiotic Pretreatment Improves FMT Response in Peanut Allergy

“There is really no evidence right now that peanut oral immunotherapy can be a disease modifier, meaning that if you stop it, your disease will actually get better,” said Rima Rachid, MD, director of the Food Allergy Program and the Allergen Immunotherapy Program, Boston Children's Hospital, in an interview with 

FMT Response Rates with and without Antibiotic Pretreatment

The phase 1 open-label trial enrolled 15 adults aged 18 to 40 years with peanut allergy confirmed by reactivity to ≤ 100 mg of peanut protein on a double-blind, placebo-controlled food challenge. Participants received 36 capsules of oral encapsulated FMT from 1 of 3 screened, non-atopic donors, dosed incrementally over 1 day for most participants.¹

The first 10 participants (part A) received FMT without antibiotic pretreatment. Three of 10 (30%; 95% confidence interval [CI], 6.7%-65.3%) achieved a threshold increase to 300 mg or 600 mg of peanut protein at 1 or 4 months.

An additional 5 participants (part B) received oral vancomycin, neomycin, and metronidazole for 4 days before FMT. In total, 3 of 5 (60%; 95% CI, 14.7%-94.7%) achieved the same efficacy threshold. Overall, 6 of 15 participants (40%; 95% CI, 16.3%-67.7%) responded after a single FMT dose, with the response persisting at 4 months in all 6; 5 of the 6 responders were male, compared with 2 of 9 nonresponders (

FMT was well tolerated across the 15 participants. Three adverse events in grades 1 and 2 occurred, consisting of fatigue, diarrhea, nausea, abdominal pain, dizziness, and headache, all resolving within 12 to 48 hours. No grade 3 or higher events occurred, and no allergic reactions were attributed to FMT administration.¹

Sex-Based Response Differences in FMT for Peanut Allergy

Rachid said that she cannot yet jump to any conclusions about the apparent sex-based difference in response. She just noted it was “interesting as an observation.”

“We will need larger studies to see if there are indeed sex differences,” she said. “It’s too early to be certain. The larger studies will require a much larger number of patients… probably 1 donor per 20 patients. This is really scratching the tip of the iceberg. In this particular study, it is showing us a very promising signal, but as usual in research, it will bring a lot of questions once we have the data.”

Rachid R, Martinez-Blanco M, Kuziel GA, et al. Fecal microbiome transplant in food allergy in humans and mice identifies a role for bile acid metabolites in oral tolerance. 

Boston Children's Hospital. How 'good' bacteria from fecal transplants reduce peanut allergy. Published August 5, 2026. Accessed August 11, 2026. 

medicalxpress.com/news/2026-08-good-bacteria-fecal-transplants-peanut.html

HCPLive. Fecal Microbiota Transplant Boosts Peanut Tolerance in Phase 1 Trial. Published August 11, 2026. Accessed August 11, 2026. 

hcplive.com/view/fecal-microbiota-transplant-boosts-peanut-tolerance-phase-1-trial

Wood and Ross. Palforzia Discontinued, Ending the Only FDA-Approved Peanut OIT Option. HCPLive. Published July 31, 2026. Accessed August 5, 2026. 

https://www.hcplive.com/view/palforzia-discontinued-ending-only-fda-approved-peanut-oit

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Rima Rachid, MD, discussed why antibiotic pretreatment before fecal microbiota transplantation may improve peanut allergy response rates.

Rima Rachid, MD

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