Oral administration of recombinant human erythropoietin in liposomes in rats: influence of lipid composition and size of liposomes on bioavailability.

Intestinal absorption of recombinant human erythropoietin (Epo) encapsulated in liposomes (Epo/liposomes) was examined by measuring the pharmacological effects of Epo after oral administration in rats. Circulating reticulocyte counts after oral administration of Epo/liposomes showed a profile different from that after intravenous administration. Epo/liposomes 0.1 micron in diameter were absorbed more effectively than those 0.2 micron in diameter. In the 0.1 micron Epo/liposomes composed of dipalmitoylphosphatidylcholine (DPPC) and soybean-derived sterols (SS), cholesterol (Ch), or soybean-derived sterylglucosides (SG), DPPC/SS (in molar ratio 7/2) and DPPC/Ch (7/2) showed higher efficiency in intestinal absorption than DPPC/Ch (7/4) and DPPC/SG (7/2) at a low dose by the sysmex method. Pharmacological availabilities for oral administration of Epo/liposomes were 0.74-31% and 3.3-30% as evaluated by circulating reticulocyte counts and percentage circulating reticulocytes of erythrocytes, respectively, in comparison to those for intravenous administration of the same dose.