Iodinated contrast media adverse reactions

Iodinated contrast media adverse reactions, popularly referred as contrast allergies, are an uncommon group of symptoms, with different degrees of severity, that may occur after the intravenous administration of these drugs. 

Along the radiology history, the iodinated contrast medias have evolved and become progressively safer. This article will approach the adverse reactions based on the use of non-ionic low-osmolar contrast agents, which are the current state-of-art option in Radiology. It is well established that these agents are safer than the older high-osmolar or ionic contrast medias. 

An increased risk for an adverse contrast reaction can be identified and assessed by the application of institutional forms and pre-exam interviews.

  • asthma: it is not a contra-indication, although these patients have 6 to 10 times more risk of developing severe contrast reactions 1. Remember that the risk of severe reactions is small (0.04% to 0.0004% of the patients receiving a non-ionic and low-osmolality iodinated contrast)
  • previous history of multiple allergies: it is not a contra-indication. A more detailed history should be obtained. Keep in mind that shellfish allergy and skin irritation/"allergy" to topic iodine antiseptic are not associated with an increased risk of contrast adverse reactions
  • History of a previous reaction to iodinated contrast media: details of the previous reaction should be obtained and alternatives (e.g. non-contrasted study, ultrasound, MRI) may be considered

Corresponds to reactions within 60 minutes after the intravenous administration of the contrast media, which do not involve antibodies, and is not dose dependent. They are referred as idiosyncratic (anaphylactoid) or "pseudoallergic" reactions, and are divided as:

  • mild: self-limiting manifestations that usually resolve without any specific treatment, e.g. nausea, vomiting, flushing, pruritus, mild urticaria, and headache. They occur in ~3% of patients receiving a non-ionic and low-osmolality iodinated contrast
    • treatment: supportive measures are enough 
  • moderate: symptoms that are more prominent and demand medical attention with specific treatment, e.g. marked urticaria, severe vomiting, bronchospasm, facial oedema, laryngeal oedema, and vasovagal attacks
    • treatment:
      • urticaria: the use of antihistamines or intramuscular adrenaline is advised in some situations
      • bronchospasm: oxygen should be offered by mask (6-10 litres/min), Beta-2-agonists (e.g. terbutaline, salbutamol) metered dose inhaler (2-3 deep inhalations), and intramuscular adrenaline should be considered if decreased blood pressure 
  • severe: reactions that usually represent a progression of the moderate symptoms and are life-threatening, e.g. respiratory arrest, cardiac arrest, pulmonary oedema, convulsions, and hypovolaemic shock. They are estimated to occur in 0.04% to 0.0004% of the patients receiving a non-ionic and low-osmolality iodinated contrast. The risk of death is rare, estimate in 1:170,000

Those reactions happening between one hour to one week after the contrast administration. They are commonly non-severe skin manifestations such as a maculopapular rash. Angioedema, erythema, and urticaria are also reported less frequently. 


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