Best Practices for Managing FPIES Reactions, With Anna Nowak-Wegrzyn, MD, PhD

New guidance on managing Food Protein–Induced Enterocolitis Syndrome (FPIES) highlights evolving strategies for both acute treatment and long-term dietary management in infants and young children. At the 2026 American Academy of Allergy, Asthma & Immunology (AAAAI) annual meeting in Philadelphia, Anna Nowak-Wegrzyn, MD, PhD, from NYU Grossman School of Medicine, discussed best practices for clinicians navigating this complex non-immunoglobulin E–mediated food allergy.

FPIES most commonly begins in infancy and typically presents with delayed gastrointestinal symptoms after ingestion of a trigger food. Unlike classic allergic reactions, symptoms usually occur 1 to 4 hours after ingestion and are characterized by repetitive, often forceful vomiting, pallor, lethargy, and occasionally diarrhea. Because skin or respiratory symptoms are typically absent, the condition can initially be mistaken for viral gastroenteritis.

“It may start on the first known feeding of the food,” Nowak-Wegrzyn said. “Maybe [the] third or fourth time the baby tolerated a small amount, [but] then they are fed a larger amount, and now 2 hours later, between 1 and 4 hours after eating, they develop vomiting. Sometimes…if it's witnessed by the parent, it's described as projectile.”

Acute management strategies have evolved as clinicians better understand the underlying inflammatory pathways involved in FPIES. Nowak-Wegrzyn noted that increasing evidence supports the use of ondansetron, a serotonin antagonist commonly used to treat chemotherapy-related nausea and vomiting. During FPIES reactions, serotonin release appears to contribute to the vomiting response, making ondansetron an effective option for symptom control.

For milder reactions, management can often occur at home. Caregivers may administer oral ondansetron and begin careful oral rehydration using small, frequent amounts of fluids such as oral rehydration solutions or breast milk. However, more severe reactions require emergency evaluation.

“FPIES is considered an allergic emergency because a subset of patients may have more severe manifestations with hypotension, with really distributive hypovolemic shock, and this will not resolve unless you can provide fluid resuscitation,” Nowak-Wegrzyn said.

These patients need intravenous fluids and, in some cases, corticosteroids to reduce the inflammatory response.

Beyond acute treatment, one of the most challenging aspects of FPIES management is determining how and when to introduce new foods after a reaction. To reduce the risk of additional reactions, clinicians typically recommend introducing foods from entirely different food groups rather than closely related foods that may carry a higher risk of cross-reactivity. For example, if an infant reacts to oat, the next food introduced might be a fruit or vegetable rather than another grain.

Initial introductions are often done gradually, starting with very small amounts and slowly increasing to a typical serving size. As infants successfully tolerate more foods, the pace of dietary expansion can usually increase.

Because diagnostic tests are typically negative in FPIES, decisions about food reintroduction often rely on clinical judgment.

“We don't attempt to reintroduce the food sooner than 6 months after the reaction, but after that, we may wait longer if the child is avoiding multiple foods and hasn't introduced all of [the] other foods,” Nowak-Wegrzyn said. “We would like to avoid a situation [where] they will get turned off and unwilling to try other foods.”

Anna Nowak-Wegrzyn has no relevant disclosures.

References

Nowak-Wegrzyn, A. Update on Diagnosis and Management of FPIES in Early Life. Session presented at AAAAI 2026 in Philadelphia on February 27, 2026.