Immediate and Late Adverse Reactions to Iodinated Contrast Media: A Pharmacological Point of View

Iodinated contrast media (CM) are widely used in radiological procedures, and carry a risk of adverse reactions with possible sequelae or death. Various and numerous reactions have been reported, most of which are transient ones and do not threaten the patient's life. Immediate adverse reactions include adverse effects directly related to the osmotic load or to the CM chemotoxicity, and immediate hypersensitivity reactions. The exact incidence of the different types of reactions is difficult to establish because not all cases are reported and because a unique severity scale is lacking. All the underlying mechanisms have not been evidenced yet, as patients are rarely properly investigated. Allergic immediate hypersensitivity probably provokes the most severe reactions, whereas non-allergic hypersensitivity determines moderate reactions. Diagnostic tools are available and consist in tryptase and histamine measurements and in skin testing. Late reactions include skin or systemic reactions due to T-lymphocytes-mediated delayed hypersensitivity, nephropathy and dysthyroidism. Delayed allergic hypersentivity can be diagnosed by skin testing with delayed reading. Allergic hypersensitivity, immediate or delayed, means immune mechanisms and is a contraindication of further administration of the culprit CM.