title: Lyophilized liposomes: a new method for long-term vesicular storage.
abstract: To facilitate acceptance and use of radiopaque liposomes as novel CT contrast agents, we developed a technique that permits their long-term storage at room temperature. This study compares standard storage procedures with the new method. Multilamellar vesicles were prepared with egg lecithin, cholesterol and stearylamine (4:1:1 molar ratio) as well as diatrizoate. After synthesis, the vesicles were separated into batches: one portion was kept frozen (FRO), another was lyophilized and stored at room temperature (LYO-RT), and a third was thawed and stored at room temperature (RT). Size, structure and biodistribution of vesicles in all three groups were assessed over a 6-month period. Freeze-drying the vesicles caused no apparent damage to their membranes The RT group showed marked aggregation after 1 month, while the LYO-RT and FRO vesicles showed only a slight shift to larger particles after 6 months. At this time, there was no significant change in the biodistribution of the LYO-RT vesicles compared to FRO. Uptakes in the reticuloendothelial tissues were 15 per cent and 19 per cent respectively. The LYO-RT materials showed additional advantages in that they were always easy to resuspend. This technique appears to be the most successful and convenient procedure for the long-term storage of liposomes.
mesh_terms: D000818:Animals; D003973:Diatrizoate / Q000493:pharmacokinetics; D004339:Drug Compounding; D004356:Drug Storage / Q000379:methods*; D005612:Freeze Drying / Q000379:methods; D007457:Iodine Radioisotopes; D008081:Liposomes; D008297:Male; D009928:Organ Specificity; D010316:Particle Size; D051381:Rats; D013696:Temperature
chemical_list: D007457:Iodine Radioisotopes; D008081:Liposomes; D003973:Diatrizoate