A 6-month-old male infant is brought to the pediatrician by his mother for an urgent evaluation following a reaction to food. Approximately 45 minutes prior to arrival, the mother fed the infant a small amount of peanut butter mixed into oatmeal for the first time. Within 10 minutes of ingestion, the infant developed redness around the mouth, which rapidly progressed to raised, red welts on his face and trunk. He became irritable and vomited once. There was no difficulty breathing, wheezing, or loss of consciousness. The mother administered an oral antihistamine at home.

The patient's past medical history is significant for moderate to severe atopic dermatitis (eczema) diagnosed at 2 months of age, requiring daily emollients and intermittent topical corticosteroids. He is currently breastfed and has recently started solid foods (rice cereal, sweet potato) without incident. There is a family history of allergic rhinitis in the father and asthma in the mother. He takes no daily medications. Review of systems is otherwise negative for fever, cough, or diarrhea.

The infant appears well-nourished and alert but irritable. He is afebrile, heart rate is 140 bpm, respirations are 30/min, and BP is 85/50 mm Hg. Capillary refill is <2 seconds.