I oversol is a monomeric, noniodinated radiographic contrast medium. It has three iodine atoms and six hydroxyl groups, but no carboxyl groups. The first monomeric, noniodinated contrast medium known was metrizamide. Second-generation monomeric, noniodinated contrast media (iopamide, ioversol, and iohexol) have intermediate viscosity and osmotoxicity; therefore, the incidence of adverse effects from them is low ( 1).
Adverse reactions occur in about 5% of contrast media examinations. The incidence of mild reactions (flushing,nausea, and headache) is high. More severe side-effects, such as asthma or anaphylactoid reactions, are rare, but the problems are serious enough to be of concern ( 2). Side-effects induced by contrast media have a complex etiology, and several pathogenic mechanisms have been suggested. Immunologic mechanisms have been proposed by some authors ( 3).
We report the case of a 44-year-old woman who had suffered an adverse reaction to ioversol 4 months before. This patient underwent intravenous urography with ioversol; she immediately developed nausea, vomiting, dizziness, hypotension (80/40 mmHg), widespread pruriginous erythema, lip angioedema, and shortness of breath. She received 6-methyl-prednisolone (60 mg intravenous), dexclorpheniramine (10 mg intramuscular), and epinephrine (0.3 mg subcutaneous). Her symptoms subsided in 4 h.
After the patient gave written consent, an allergy study was carried out. Skin prick tests were performed with sodium and meglumine amidetrizoate (Urografin 76%; 20 ml; Schering AG, Germany), iopromide (Clarograf 300; 100 ml, iopromide DCI 623 mg/ml), and iodinated polyvinylpyrrolidone (Betadine 7.5% and 10% solutions; 100 ml, Asta Médica, Spain). The results of all of them were negative in our patient. We then performed a skin prick test with ioversol (Optiray 320; 100 ml; ioversol DCI 678 mg/ml, Mallinckrodt Medical, Spain), and we obtained a positive result (wheal of 8×8 mm with pruritus and erythema). Skin prick tests with ioversol were also performed in 50 control subjects (25 of whom were atopic subjects), with negative results. Positive (histamine; 10 mg/ml) and negative (saline serum 0.9%) controls were also carried out. Serum total IgE was 231 kU/l. The histamine-release test with ioversol was negative. To develop this test, we used the automated fluorometric method described by Siraganian ( 4) and Hook, with the Technicon Autoanalyzer II.
We present a patient who developed anaphylactic shock caused by ioversol. The symptoms suffered by the patient, the latency of the reaction, and the positivity of the skin prick test with ioversol strongly suggest an underlying type-I, IgE-mediated hypersensitivity mechanism. In vitro tests have a high potential utility in the diagnosis of adverse reactions to drugs. However, their sensitivity is low; the value of the in vitro histamine release for the diagnosis of drug-induced anaphylaxis appears to be poor. Therefore, this test is scarcely used for the diagnosis of drug allergy ( 5).