The increased histamine release in ischaemic heart disease patients undergoing coronaroangiography is not mediated by specific IgE

Anaphylaxis to iodinated contrast material: nonallergic hypersensitivity or IgE-mediated allergy?

OBJECTIVE

Contrast material is generally well tolerated although approximately 1% of patients who receive low-osmolar nonionic contrast material will develop anaphylaxis symptoms. Because most anaphylactic reactions are mild and nonallergic, clinically mimicking immunoglobulin E (IgE)-mediated allergy, diagnostic skin testing has been discussed controversially in the past and prophylactic pretreatment drug regimens are recommended instead. In the past 6 years, all patients with contrast material-induced anaphylaxis have been subjected to allergologic diagnostic procedures to clearly differentiate allergic and nonallergic anaphylaxis. Thus the purpose of our study was to identify and differentiate IgE-mediated allergy and nonallergic contrast material-induced hypersensitivity. Furthermore, the objective of our diagnostic procedures was not only to identify the culprit contrast material but also to find alternative contrast material for future radiologic interventions.

SUBJECTS AND METHODS

We evaluated 96 patients with anaphylaxis symptoms after contrast material application using standardized intradermal skin testing. In patients with positive skin tests, the IgE-mediated allergy was further evaluated with in vitro and challenge tests.

RESULTS

In four patients (suffering from anaphylaxis grades 2 and 3) out of the 96 (4.2%), skin tests and basophil activation tests strongly suggested IgE-mediated allergy to the contrast materials iopromide (two patients), iomeprol, and iopentol. In two patients with allergies to iopromide and iomeprol, alternative nonionic monomer contrast materials were tolerated, as identified in controlled challenge tests with iopamidol and iopromide, respectively.

CONCLUSION

The evaluation of patients with contrast material-induced anaphylaxis (at least those with anaphylaxis > or = grade 2) should always include appropriate skin tests ensuring that patients with an IgE-mediated allergy are not missed. Moreover, allergologic testing may identify a contrast material of the group of nonionic monomers that will be tolerated in future radiologic interventions.

Monitoring non-immediate allergic reactions to iodine contrast media

Non-immediate reactions to iodine contrast media (ICM) affect 2-5% of patients receiving these agents. We studied the immunological mechanisms involved in patients with a confirmed non-immediate reaction, maculopapular exanthema, after administration of ICM. The diagnosis was carried out by skin testing or drug provocation test. The immunological study was performed in sequential peripheral blood mononuclear cells taken from the onset of the reaction by flow cytometry and in skin biopsy by immunohistochemistry, with specific recognition by the lymphocyte transformation test (LTT) with different ICM. Flow cytometry showed an increase in the different activation markers [CD69, CD25 and human leucocyte antigen D-related (HLA-DR)] and the skin homing receptor [cutaneous lymphocyte-associated antigen (CLA)] in CD4 lymphocytes, whereas perforin was higher in the CD8 lymphocytes. The skin biopsy showed a perivascular mononuclear infiltrate composed of CD4 lymphocytes, expressing CD25, HLA-DR and CLA, with eosinophils. Intradermal skin tests and the LTT were positive to several ICM, including the culprit agent in four and three patients, respectively, with negative results in all 10 tolerant controls. We showed that a specific immunological mechanism was implicated in patients with non-immediate reactions to ICM. Moreover, the positive results in skin tests and lymphocyte proliferation tests indicated that an important cross-reactivity exists.

A prospective randomised controlled trial to determine the early and late reactions after the use of iopamidol 340 (Niopam™) and iomeprol 350 (Iomeron®) in cardiac catheterisation

A new generation of intravascular contrast agents, the non-ionic monomers have safety profiles that are superior to those of older ionic compounds. There are, however, significant differences between these agents.

AIM

The aim of this study was to determine the incidence of early (<24h) and late (>24h to 7 days) reactions to two non-ionic contrast agents currently used during cardiac catheterisation: iopamidol 340 (Niopam Bracco UK Ltd.) and iomeprol 350 (Iomeron Bracco UK Ltd.).

METHODS

This was a prospective, randomised, double blinded trial. One thousand nine hundred and eighty-five patients undergoing cardiac catheterisation received one of the following contrast agents on a weekly basis: iopamidol 340 (Niopam) and iomeprol 350 (Iomeron). Reactions that were possibly related to the contrast agents were recorded on predefined data collection forms during the first 24h of the procedure (early reaction) and after 24h to 7 days (late reaction) by means of a questionnaire.

RESULTS

The baseline characteristics were matched in both the groups. There was no significant difference in the incidence of heat sensation experienced between the two groups (p=0.1). Early non-heat reactions occurred in 2.7% of patients receiving iopamidol 340 (Niopam) and 4% of those receiving iomeprol 350 (Iomeron) (p=0.1). Significant electrocardiographic changes were recorded in 1.7% of patients who received iopamidol 340 (Niopam), and 1% of those who received iomeprol 350 (Iomeron) (p=0.2). Bradycardia occurred more frequently in the iopamidol 350 group (0.8%) compared to the iomeprol 350 group (0.1%) p=0.02. Late reactions occurred in 16.2% of those receiving iopamidol 340 (Niopam) and 21.7% of those receiving iomeprol 350 (Iomeron) (p=0.02). A total of 23 (3.7%) patients in the iopamidol group and 39 (6.2%) patients in the iomeprol group reported nausea, p=0.01.

CONCLUSIONS

The incidence of early adverse reactions was similar with the two non-ionic contrast agents. Although bradycardia was slightly more frequent using iopamidol 340, nausea was reported more commonly 24h after the procedure in patients receiving Iomeron 350 (Iomeron). We conclude that there were only minor clinical differences between these agents; both are safe and well tolerated.

Review article: Acute serious and fatal reactions to contrast media: our current understanding

Serious or fatal reactions to a contrast medium (CM) are unpredictable but fortunately rare. History of serious reaction to CM, bronchial asthma or multiple allergies increases the incidence of serious reactions by a factor of 5. Serious or fatal reaction to CM could be due to direct effect on basophils and mast cells or IgE mediated (type 1 hypersensitivity reaction). Activation of the kinin system leading to the formation of bradykinin could also be involved. Complement activation is unlikely to be a primary factor in initiating a serious reaction to CM. Avoiding CM administration in patients at high risk of serious reaction is advisable, but if the administration is deemed essential all precautions should be implemented and measures to treat serious reactions should be readily available. Oxygen supplementation, intravenous administration of physiological fluids and intramuscular injection of 0.5 ml adrenalin (1:1000) should be considered in the first line management of acute anaphylaxis. The ability to assess and treat serious CM reaction effectively is an essential skill that the radiologist should have and maintain.

Allergy-like reactions to iodinated contrast agents. A critical analysis

Allergy-like reactions may occur following administration of iodinated contrast media (CM), mostly in at-risk patients (patients with history of previous reaction, history of allergy, co-treated with interleukin-2 or beta-blockers, etc.) but remain generally unpredictable. Severe and fatal reactions are very rare events. All categories of CM may induce such reactions, although first generation (high osmolar CM) have been found to induce a higher rate of adverse events than low osmolar CM. However, no differences were found between the two categories of CM with respect to mortality. Delayed reactions can also occur. There are no differences between the various categories of CM except for non-ionic dimers, which are more likely to induce such effect. Numerous clinical studies have evaluated the prophylactic value of drugs (mostly antihistamines and corticosteroids). Results are unclear and highly variable. Any prevention depends upon the mechanism involved. However, the mechanism of CM-induced allergy-like reaction remains disputed. Relatively recent data revived the hypothesis of a type-I hypersensitivity mechanism. Positive skin tests to CM have been reported. However, the affinity of IgE towards CM has been found to be very low in the only study which actually evaluated it. Other pathophysiological mechanisms (involving direct secretory effects on mast cells or basophils, or activation of the complement system associated or not with the plasma contact system) are also much debated. Anaphylaxis and anaphylactoid reactions are, in the end, clinically undistinguishable.

Cross-reactivity among drugs: clinical problems

Cross-reactivity among drugs is either mediated by immunologic mechanisms or not. The former kind is usually explained by the presence of common antigenic determinants in the cross-reacting drugs. In the case of compounds provoking non-allergic hypersensitivity reactions, cross-reactivity is explained by a common pharmacological characteristic, such as the inhibitory effect of non-steroidal anti-inflammatory drugs on cyclooxygenase-1 and the capability of muscle relaxants or contrast media to release histamine through a non-immunologic mechanism. The main clinical problem deriving from cross-reactivity among drugs is the compelling need to choose a potentially cross-reactive compound and, therefore, to assess cross-reactivity by diagnostic tests. In choosing alternative compounds, skin testing has been used in evaluating IgE-mediated cross-reactivity between penicillins and cephalosporins, as well as among muscle relaxants. In assessing T cell-mediated cross-reactivity among contrast media, corticosteroids, anticonvulsants and heparins, delayed-reading intradermal tests and patch tests, together with lymphocyte transformation tests, can be performed. Because of the limited sensitivity of in vivo and in vitro testing, the most prudent way of establishing the tolerability of a compound of the same group in patients who especially require one is a graded challenge when other allergologic tests are negative.