Current contrast media and ioxilan. Comparative evaluation of vascular pain by aversion conditioning

Vascular pain caused by contrast media (CM) cannot be quantified by subjective patient reports or manifest pain reactions in experimental animals. Therefore, conditioned taste aversion (CTA), a psychopharmacological method, was used in double-blind femoral arteriography in rats to compare a new nonionic monomeric CM, ioxilan, with iohexol, iopamidol (all at 350 mgI/mL) and 22% sorbitol. A chronically implanted femoral artery catheter was used to inject 0.2 mL/kg body weight. By measuring the intake of water laced with the flavor that thirsty rats had learned to associate with the injection, the degree of aversion, assumed proportional to pain, was determined. Ioxilan (690 mOsm) produced the least pain, followed by iopamidol (810 mOsm), iohexol (844 mOsm) and sorbitol (1410 mOsm). Since all test substances are highly and similarly hydrophilic and nonionic, the intensity of vascular pain must depend on solution osmolality, rather than on chemotoxicity or ionicity. Compounds of the lowest osmolality, ig, ioxilan, elicit the least vascular pain.