Adverse reactions to contrast agents

Use of iodine contrast agents is contraindicated in pregnancy because they can cross the placenta and interfere with foetal thyroid development. 

Special precautions should be taken in patients with known hypersensitivity to iodine and in those with other allergies, for example to foods or other drugs. Prophylactic corticosteroids, for example prednisolone, are recommended as premedication 12-18 hours prior to imaging in such high-risk patients. 

Contrast agents should also be used with caution in patients with epilepsy because they can provoke seizures in hepato-renal syndrome (renal failure following liver cirrhosis and jaundice) in severe respiratory disease, especially asthma and in diabetes. 

Iodine contrast agents interact with metformin, an oral hypoglycaemic drug used to treat type 2 diabetes (see Chapter 6). Iodine contrast agents increase the risk of a patient developing lactic acidosis with metformin, particularly if their kidney function is impaired. Metformin has to be stopped prior to radiological examination and should not be restarted until normal renal function has resumed. 

With intravenous administration, there is always a risk of damage to veins through mechanical or chemical means. A good cannulation technique is essential to avoid extravasation, tissue damage or the introduction of air into the circulation. Air embolism is a rare but life-threatening complication. Techniques that puncmre the skin can introduce infection through poor aseptic technique or contaminated equipment. Antihistamines and corticosteroids, if needed for adverse reactions, should never be mixed in the same syringe because precipitation would occur. 

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Adverse reactions to contrast agents have been linked to an in vivo interaction with enzymes involved in cholinergic activity. However, experimental results on this topic are conflicting. In a study of the in vivo effects of the non-ionic... 

Ansell G. Adverse reactions to contrast agents. Scope of problem. Invest Radiol 1970 5(6) 374-91. 

Management of acute adverse reactions to contrast agents... 

Serious adverse reactions to contrast agents are rare occurrences and the vast majority are of a minor nature. The management of serious adverse reactions to contrast agents... 

The most serious adverse reaction to contrast agents is anaphylactic shock, which must be treated as an emergency. See Chapter 3 for details of allergic reactions to drugs. In this type of hypersensitivity reaction, the contrast agent causes the release of histamine from mast cells and basophils. 

Adverse reactions to intravascular iodinated agents are usually classified as minor, intermediate, or severe life-threatening. All types of reactions to low-osmolar contrast media are five times less common than reactions to high-osmolar contrast agents (SEDA-22, 489) (SEDA-23, 494) (SEDA-24, 519), and very severe adverse reactions to contrast media are rare, with a frequency of about 0.04% with high-osmolar agents and 0.004% with low-osmolar agents. However, there are no important differences in the safety profiles of the different low-osmolar non-ionic monomers (18). 

In another survey, the incidence of contrast media reactions after intravenous administration was evaluated over 14 years (25). The incidence of all reactions to contrast media was 6-8% with high-osmolar contrast media and only 0.2% with low-osmolar non-ionic agents. Most of the reactions (over 90%) were aUergic-like, and severe reactions were rare (0.05%). One death was reported after the use of a low-osmolar agent. These data are compatible with previous reports, which showed that low-osmolar contrast media have a much better safety profile than high-osmolar media and that there is no significant difference in the incidence of acute adverse reactions between non-ionic dimeric and monomeric contrast media. 

The incidence of delayed adverse reactions to various non-ionic monomers in Japanese patients undergoing contrast-enhanced CT has been compared with the incidence in control patients who did not receive contrast. Delayed reactions occurred in 12% of patients who received contrast compared with 10% in the control group. The authors concluded that the frequency of delayed reactions that can be attributed to contrast media is 2.1%. The most common reactions were itching and limited urticaria (28). This report highhghts the difficulty of verifying that adverse events that occur many hours after contrast administration are directly caused by the contrast agent. 

Racial differences could be a factor in the high incidence of delayed skin reactions to contrast media in Japan, as 43% of Japanese are deficient in acetaldehyde dehydrogenase. This deficiency results in the accumulation of acetaldehyde, which potentiates the ability of contrast agents (especially dimers), to bridge proteins, which is a probable causative factor in many of their adverse effects (11). 

The adverse effects of contrast agents during computed tomography (CT) are broadly similar to those during excretion urography, but the incidence of serious reactions and deaths may be higher, because reactions are harder to treat when the patient is in a scanner (SEDA-7, 451). Renal insufficiency can occur in patients with diabetes and pre-existing renal disease or as a result of multiple examinations. In Herpes simplex encephalitis. 

Strieker BH, Psaty BM. Detection, verification, and quantification of adverse drug reactions. Br Med J 2004 329(7456) 44-7. Thomsen HS, Marckmann P, Logager VB. Nephrogenic systemic fibrosis (NSF) a late adverse reaction to some of the gadolinium based contrast agents. Cancer Imaging 2007 7 130-7. 

Contrast agents are among the safest medicinal products in use. They are not intended to have pharmacological activity nevertheless adverse reactions are possible. Adverse reactions to iodine contrast agents are related to iodine concentration, osmolality, whether the agent is ionized or not, the rate and frequency of injection and the dose given and... 

Adverse reactions to iodine contrast agents, rated mild, moderate and severe are listed in Table 13.2. Conventionally, mild adverse reactions need reassurance of the patient but no treatment moderate adverse reactions may interfere with radiological examination but usually require no treatment and severe adverse reactions require the examination to be stopped and emergency treatment. 

Adverse reactions to iodine contrast agents are rare, especially with the newer non-ionic dimers of low osmolality. Adverse reactions range from mild effects, such as nausea and vomiting, to moderate effects, such as erythema and chest pain. Severe adverse reactions, for example bronchospasm and anaphylactic shock, always need emergency treatment. 

Give three mild and three moderate adverse reactions to iodine contrast agents. What should be done about them ... 

The systems that cause the most trouble are those in which the drug is dissolved in water, in contrast to ethanolic matrices, which are uncommonly erythema-togenic. The evidence strongly favors hydration as the etiologic agent in most adverse reactions to transder-... 

As with every administered pharmaceutical agent, adverse reactions to iodinated contrast media do occur, but the incidence is low. Reactions can be unrelated to the dose or concentration of the solution administered (see below) or they can be dose dependent. An important contributor to the latter category is the osmolaUty of the administered agent which is responsible for the feelings of discomfort. 

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