Production and characterization of improved liposomes containing radiographic contrast media

The authors have investigated liposomes prepared by the reverse-phase evaporation method (REVs) and a modification of this technique that employs a microemulsifier (MREVs), for the delivery of radiographic contrast media (RCM) to the liver and spleen. The modification entailed substituting a Microfluidizer (Microfluidics Inc., Newton, MA) for the sonication step of the REV technique. The MREV procedure is amenable to large-scale production and continuous-flow operation and yields products with high RCM encapsulation. Efficiently entrapped are ionic, high-osmolar diatrizoate (24.38 +/- 2.62% versus 8.35 +/- 0.55%; MREV versus REV), and nonionic, low osmolar Iotrolan (Schering AG, Berlin, FRG) (24.84 +/- 2.13% versus 7.25 +/- 1.19%) RCM with iodine-to-lipid ratio of 1.5:1. The MREV procedure, therefore, has practical advantages over the REV method. High liver and spleen uptakes of Iotrolan-containing vesicles were noted in normal rats. The diatrizoate MREVs lost their contents on contact with serum, resulting in urinary excretion of this agent. Computed tomography values of splenic and hepatic sections, 1 hour after intravenous injection of Iotrolan MREV (500 mgI/kg), are 0.78, and 0.08 Hounsfield Units (HU)/mgI/kg, respectively (versus 0.01, and 0.006 HU/mgI/kg for free Iotrolan).