[Uroangiographic contrast media, today. Elements of interest for the urologist]

Uroangiographic contrast media, as well as magnetic resonance or ultrasound contrast agents, are substances which are able to artificially enhance the contrast between different tissues, or between normal tissue and pathological areas. The design of ionic and nonionic, monomeric or dimeric, iodobenzene derivatives is outlined with attention given to historical developments and breakthroughs. Relationships between physicochemical properties (osmolality, viscosity, molecular structure, etc.) and pharmacological profile are described. Nonionic compounds display favourable physicochemical characteristics: high water solubility, low osmolality and viscosity and good systemic tolerability. Recent surveys on adverse reactions to uroangiographic iodinated contrast media have shown that the risk of severe reactions is about six times lower with nonionic than ionic X-ray contrast agents. The pathogenetic mechanisms of adverse reactions, generally classified as either anaphylactoid or osmotoxic and chemotoxic, are still not well understood. It has been proposed that leukotrienes, prostaglandins, kinins, etc., may be involved. Nitric oxide appears to play a crucial role in the final common pathway by which anaphylaxis-like reactions occur in response to contrast agent administration. The margin of safety (median lethal dose/diagnostic dose) for nonionic compounds is two- to three-fold greater than for ionic compounds. As a look at the future, an approach to molecules potentially useful as "blood pool X-ray contrast agents" is based on iodinated dendrimeric macromolecules, in which the core is triazacyclononane and branches are represented by trioodobenzene derivatives.