Investigations on the transfer of porphyrin from o/w emulsion droplets to liposomes with two different methods.

Due to their small particle size, colloidal fat emulsions are suitable for intravenous administration. In order to obtain information on their potential in vivo performance, it is important to find a simple and effective in vitro assay to evaluate the drug release behavior of such particles. Two in vitro methods were studied to measure the transfer of a lipophilic model drug from colloidal o/w emulsion droplets (donor) to liposomes (acceptor), which serve as model membranes mimicking cell membranes in the body. In the first method (column method) the acceptor particles were neutral unilamellar vesicles. In the second method (MLV method), multilamellar vesicles (MLV) were used as acceptor. The donor nanoemulsions were prepared by high pressure homogenization. Z-average particle size, polydispersity index and zeta potential were determined. The transfer of porphyrin was moderate to the acceptor MLV and rapid to the acceptor unilamellar vesicles. The amount of transferred porphyrin at the end of the experiment depended on the transfer method and the donor/acceptor ratio. With both acceptors the transfer of porphyrin stopped at a concentration lower than the theoretical equilibrium values. Many factors such as acceptor particle size and donor to acceptor lipid molar ratio affect the drug transfer from the donor particles to the different acceptors. Both methods seem to be suitable to study the drug transfer from such colloidal emulsion and the use of lipophilic acceptor particles is a better approach to the conditions in blood.