1995 Volume 18 Issue 7 Pages 1020-1023
The effect of the vesicle size on in vivo release of daunorubicin, an anthracycline anticancer drug, from liposomes into the circulation was studied in rats. The liposomes were prepared from hydrogenated egg phosphatidylcholine (HEPC) or egg phosphatidylcholine (EPC), cholesterol and dicetylphosphate at a molar ratio of 5 : 4 : 1, and their mean vesicle sizes were adjusted to about 50 and 100 nm. The drug retained in the liposomes and the drug that leaked were separated from plasma by gel filtration. On the assumption that the lipid content does not change, the drug release from each liposome preparation was estimated from the latency (%) calculated from the drug/lipid concentration ratio of the liposome preparation. From HEPC-liposomes with a diameter of 50 nm, the drug was released gradually after intravenous administration, and the cumulative percent release of the drug reached 40% after 240 min. However, from EPC-liposomes with the same size, 50% of the drug was released within 5 min, and more than 90% of the drug was released within 60 min. From HEPC-liposomes with a diameter of 100 nm, no drug release was observed for 240 min after administration. These findings indicate that the vesicle size and the lipid composition of liposome preparation affect the in vivo drug release.