Case of Polyethylene Glycol Allergy Confirmed with Basophil Activation Test and Oral Challenge Successfully Immunized with SARS-CoV-2 Vaccine

Polyethylene glycols (PEG) or macrogols are polymers of ethylene oxide widely used in drugs either as active substances or, more commonly, as excipients. We report a Caucasian 32-year-old woman with referred anaphylaxis almost instantly after oral intake of a macrogol-containing laxative. Despite an anaphylactic reaction, the patient showed negative results for both the skin test and specific IgE to the monomer, while the basophil activation test and oral challenge were positive. The patient was later successfully vaccinated with a polysorbate 80-containing SARS-CoV-2 vaccine following an additional work-up. As a result, the inactive form of PEG cannot be fully diagnosed, and it is considered a “hidden” allergen. PEG derivatives like polysorbates need special consideration due to their possible cross-reactivity.