Visipaque is isotonic to human and rat blood plasma

Even at its highest concentration, 320 mg I/ml, Visipaque - based on the nonionic dimer iodixanol - is isosmotic to blood plasma, whereas Omnipaque (300 mg I/ml)-based on the nonionic monomer iohexol - has an osmolality of about twice that of the plasma. However, the fact that a solution is isosmotic to plasma does not necessarily mean that it is isotonic to plasma. An isosmotic solution can still cause a net movement of water over the plasma membranes of, for example, erythrocytes and endothelial cells. Determination of the tonicity of Visipaque 320 mg I/ml and comparison with that of Omnipaque 300 mg I/ml and hypertonic NaCl have been performed. No change in the water content of human erythrocytes was seen after mixing whole blood 10:1 with either Visipaque 320 mg I/ml or 155 mM NaCl, whereas a significant decrease in water content occurred with Omnipaque 300 mg I/ml and 620 mM NaCl. No difference in the water content of rat erythrocytes was evident after mixing whole blood with Visipaque 320 mg I/ml or isotonic NaCl. However, as with human erythrocytes, a significant decrease in water content occurred after rat blood was mixed with Omnipaque 300 mg I/ml. In conclusion, Visipaque 320 mg I/ml does not cause any net movement of water over the human or the rat erythrocyte plasma membrane, i.e., Visipaque is isotonic to human and rat blood plasma.