Anaphylaxis: A Rapid-Onset, Life-Threatening Allergic Reaction
Anaphylaxis is a serious, systemic allergic reaction that occurs rapidly and can be fatal if not treated promptly. It is classified as a type I hypersensitivity reaction, mediated by immunoglobulin E (IgE) antibodies that trigger the release of histamine and other inflammatory mediators from mast cells and basophils. Once the allergen is introduced into the body, the reaction may progress within minutes, sometimes even seconds. The hallmark symptoms involve multiple organ systems, including respiratory distress (e.g., wheezing, throat tightness), cardiovascular compromise (e.g., hypotension, tachycardia), cutaneous reactions (e.g., hives, flushing, angioedema), and gastrointestinal symptoms (e.g., nausea, vomiting, diarrhea). Common allergens that trigger anaphylaxis include certain foods (e.g., peanuts, shellfish), medications (e.g., penicillin, NSAIDs), insect stings, and latex. Prompt administration of intramuscular epinephrine is the first-line treatment, followed by supportive measures such as antihistamines, corticosteroids, oxygen, and intravenous fluids. Anaphylaxis is a medical emergency requiring immediate recognition and intervention to prevent death or long-term complications. Increasing awareness, timely diagnosis, and availability of epinephrine autoinjectors are essential to improving outcomes in individuals at risk.
PEG Anaphylaxis: An Emerging Concern in Modern Medicine
Although PEG is well tolerated by most individuals, accumulating evidence indicates that it can elicit clinically significant immune responses in a sensitized subset of patients. PEG-mediated anaphylaxis remains uncommon; however, it has gained increasing clinical and regulatory attention following severe hypersensitivity reactions associated with PEG-containing products and PEGylated therapeutics.
Omontys® Injectable, also known as peginesatide, provides a compelling example. Omontys was a PEGylated erythropoiesis-stimulating agent approved for the treatment of anemia in patients undergoing dialysis, with each therapeutic dose delivering approximately 2.56 mg of 40 kDa PEG. Shortly after its market introduction, the FDA Adverse Event Reporting System documented more than 49 cases of immediate-onset anaphylaxis, including fatal reactions, many of which occurred after the first dose. These serious safety events ultimately led to the voluntary withdrawal of Omontys from the market in 2013. This case demonstrates that PEG-containing products may pose clinically important risks in susceptible patients, even when PEG exposure appears acceptable during preclinical and clinical development.
Ultrasound enhancing agents represent another important example. Historically, many clinicians and echocardiography laboratories did not routinely assess patients for potential cross-reactive hypersensitivity to product constituents such as PEG, and awareness of PEG-related reactions associated with these agents was limited. In 2007, after several deaths and multiple serious adverse events were reported shortly after ultrasound enhancing agent administration, the U.S. Food and Drug Administration issued a boxed warning contraindicating their use in patients with severe or unstable cardiopulmonary disease and requiring a 30-minute monitoring period after administration. In 2021, following an FDA MedWatch alert describing hypersensitivity reactions in patients with preexisting PEG allergy—including 11 cases of anaphylaxis and 2 deaths after exposure to ultrasound enhancing agents—the package inserts for PEG-containing lipid-based agents, including Definity® and Lumason®, were updated to identify PEG hypersensitivity as a contraindication.
The global use of lipid nanoparticle mRNA COVID-19 vaccines has further intensified interest in PEG exposure because these vaccines contain PEGylated lipid components and have been administered in billions of doses worldwide. Although these vaccines have demonstrated a favorable overall safety profile, the long-term implications of widespread PEG exposure and potential PEG sensitization for future use of PEG-containing drugs, biologics, and medical products remain incompletely understood.
Collectively, these examples highlight an important unmet need in both drug development and clinical practice: the ability to identify patients at elevated risk for PEG-mediated hypersensitivity before exposure. As the PEGylated drug market continues to expand, proactive risk-assessment strategies—including reliable anti-PEG IgE screening in appropriate clinical and development settings—may help reduce preventable adverse events, support safer use of PEG-containing therapeutics, and strengthen confidence among patients, clinicians, and regulators.