Characterization of iopromide liposomes.

Rationale And Objectives: Iopromide-carrying liposomes were prepared and were characterized pharmaceutically and biologically.

Methods: The liposomes were prepared by the ethanol evaporation method and were characterized by quasi-elastic light scattering (size) and equilibrium dialysis (encapsulation efficiency and stability). Acute and subchronic toxicity was tested in mice and/or rats and cardiovascular tolerance in rabbits. Pharmacokinetic parameters were determined in rats. Computed tomography (CT) imaging efficiency was obtained from rat and rabbit studies.

Results: The mean diameter was 0.5 +/- 0.1 micron and the encapsulation efficiency ranged between 30% and 40%. The liposomes were stable in human and rabbit plasma for approximately 24 hours. The LD50 in mouse and rat was approximately 3 g iodine/kg. In a subchronic toxicity study in rats with six doses of 1 g iodine/kg given every three days, no adverse effects were observed. The pharmacokinetics in rats were dose-dependent. Increasing the dose resulted in lower total clearance, and longer terminal half-life. Elimination of iodine was complete and the main route of excretion was via the kidneys. A clinically relevant computed tomography enhancement of the liver was reached after approximately 200 mg iodine/kg in rats and 150 mg iodine/kg in rabbits.

Conclusions: The iopromide-carrying liposomes were well tolerated in animal studies and seemed to be suitable for the imaging of the liver.