Liposomes carrying diatrizoate. Characterization of biophysical properties and imaging applications

We have prepared and characterized a suspension of liposomes carrying diatrizoate. Vesicles were made with egg lecithin, cholesterol, and stearylamine in a 4:1:1 molar ratio, and contained meglumine sodium diatrizoate in their aqueous phase. They ranged up to 2.0 microns in size and had a multilamellar structure. These vesicles were then injected into normal and tumor-bearing rats, as well as normal dogs and a baboon. The iodine component proved to have a prolonged blood pool residence time, was cleared through reticuloendothelial and urinary tissues, and was completely excreted within seven days. The LD50 in mice was 2.3 g I/kg (38.5 g of liposome suspension/kg). Imaging studies with diatrizoate-carrying liposomes demonstrated marked and prolonged contrast enhancement of blood pool, liver, spleen, kidneys, urine, and tumor rims. Furthermore, the blood, liver, and spleen opacification was greater and longer sustained than when an equivalent amount of iodine in free diatrizoate was used. These diatrizoate-carrying liposomes are particularly well suited for computed tomographic imaging of blood pool and reticuloendothelial structures.