as an excipient has been in widespread use. The risk of sensitization appears to be higher with injectable drugs with higher-molecular-weight PEG; anaphylaxis associated with bowel preparations containing PEG 3350 to PEG 4000 has been noted in case reports.9,10 The reports include anaphylaxis after a patient was exposed to a PEG 3350 bowel preparation; anaphylaxis subsequently developed on the patient’s first exposure to a pegylated liposome microbubble, PEGLip 5000 perflutren echocardiography contrast (Definity), which is labeled with a warning about immediate hypersensitivity reactions.11 For drugs such as methylprednisolone acetate and injectable medroxyprogesterone that contain PEG 3350, it now appears that the PEG component is more likely than the active drug to be the cause of anaphylaxis.9,12 For patients with a history of an anaphylactic reaction to the SARS-CoV-2 Pfizer–BioNTech mRNA vaccine, the risk of anaphylaxis with the Moderna SARS-CoV-2 mRNA vaccine — whose delivery system is also based on PEG 2000, but with different respecti