Perflutren lipid microspheres for echocardiogram contrast: A clinical case of anaphylaxis to the non-PEGylated component

Background Perflutren lipid microsphere suspension, sold under the brand name Definity®, is a microbubble ultrasound contrast agent. The microspheres contain octafluoropropane (C₃F₈) gas encapsulated by an outer lipid shell of phospholipids and a polyethylene glycol (PEG)ylated phospholipid. Anaphylaxis to perflutren (Definity®) lipid microspheres is rare, with only one case report attributing the reaction to the PEG excipient. We report a novel case of anaphylaxis likely caused by a non-PEGylated component of Definity®. Case Presentation: Our patient is a healthy 54-year-old female, who underwent an exercise stress transthoracic echocardiogram using perflutren (Definity®) as an enhancing agent. She experienced anaphylaxis within 15 minutes of injection. Symptoms resolved after she was treated with diphenhydramine (Benadryl®) and epinephrine, followed by a systemic corticosteroid and ondansetron in the Emergency Department. The patient underwent allergy testing at our clinic for perflutren (Definity®) and various PEG-containing substances. While all PEG products tested negative, she had a positive intradermal test to perflutren. She also passed an oral challenge to PEG 3350, thus ruling out PEG as the causative agent of anaphylaxis. Conclusions Our case report highlights a previously undocumented instance of IgE-mediated anaphylaxis to Definity® with a non-PEGylated component as the likely culprit. It provides critical information to physicians on the potential risks of using Definity® and contributes to growing research surrounding the profile of Definity®.