COMPLEMENT ACTIVATION AND HISTAMINE-RELEASE FOLLOWING ADMINISTRATION OF ROENTGEN CONTRAST-MEDIA

Anaphylactoid reactions following administration of roentgen contrast media (CM) have occasionally been described. In this investigation, bl ood samples from nonallergic human volunteers were exposed to the CM i odixanol (Visipaque), iohexol (Omnipaque), ioxaglate (Hexabrix) and me trizoate (Isopaque 350). The degree of activation of the complement ca scade and the amount of free histamine in the samples were estimated. By using a hemolytic assay, a dose-independent complement consumption was detected when salt-free dilutions of the CM were added to human se rum. Very little complement consumption was detectable when the concen trations of salts in the CM solutions were adjusted toward normal plas ma concentrations, indicating that the lack of salts in the CM formula tions was responsible for causing the consumption of complement rather than the CM molecules themselves. By using an ELISA assay for determi nation of the terminal complement complex (TCC), no increase in TCC le vel was detected following the addition of iodixanol to human serum. T he results indicate that iodixanol does not activate the complement ca scade when added to human serum, and that it is unlikely that anaphyla ctoid reactions observed in man after CM administration are caused by CM-induced anaphylatoxins. No histamine release was observed following the addition of ioxaglate, metrizoate, iohexol or iodixanol to blood from nonallergic individuals.