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The American College of Radiology (ACR) recently reported concerns about certain ultrasound contrast agents. These are used in imaging tests to help improve the visibility of blood flow and blood tissues.

The federal Food and Drug Administration (FDA) has notified healthcare professionals that Definity, Definity RT, and Lumason—three brands of ultrasound contrast agents—contain a chemical called polyethylene glycol (PEG) and should not be administered to patients who may be allergic to PEG.

What is Polyethylene Glycol?

Polyethylene glycol (PEG) is a chemical compound that has many applications in the medical, chemical, and industrial industries. It is colorless, inert, odorless, and non-volatile. It’s also very soluble in water and other solutions.

The most common application of PEG in the medical industry is its use in laxatives. It draws water into the waste matter, providing a laxative effect. It’s also used in pharmaceutical creams, ointments, and medical solvents.

PEG can couple itself with other molecules, so it can be used as an inactive substance to deliver other substances. That’s what it does in ultrasound contrast agents.

Some Patients May Be Allergic to PEG

The ultrasound contrast agents included in the FDA’s warning are comprised of lipid (fat)-coated microbubbles filled with gas. Definity, for instance, doesn’t contain iodine, radioactive materials, or gadolinium like other contrast agents. Instead, after it’s injected into a patient, it produces small and consistently sized microbubbles that can pass through blood vessels.

The physical acoustic properties of these microbubbles are lower than those in blood and thus enhance the visibility of blood and tissues during an ultrasound.

PEG is frequently used in contrasting agents, including ultrasound contrast agents. Yet people can be allergic to it, and in some cases when exposed, may experience life-threatening anaphylaxis.

In a 2016 study, researchers reported on a patient experiencing recurrent severe allergic reactions to several drugs. Doctors discovered that the patient was allergic to the PEG in those drugs. The researchers concluded that cases of immediate PEG hypersensitivity are reported: “with increasing frequency.”

In a later 2019 study, researchers noted that PEG allergies may be “under-recognized” in clinical practice.

Some Patients May Be Allergic to PEG

At the time of the ACR report, the FDA was aware of reports of PEG allergies related to ultrasound contrast agents, including 11 cases of anaphylaxis and two deaths. These appeared related to the administration of either Definity or Lumason among patients with a reported history of PEG allergy.

The FDA warned healthcare professionals to confirm that patients do not have a known or suspected PEG allergy before administering these agents.

For those patients who may be unaware of a PEG allergy, healthcare professionals should ask about allergies to common PEG-containing products like certain colonoscopy bowel preparations and laxatives. Personnel should also be ready to address any allergic reactions that may occur after the administration of the contrast agents.

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