Study of in vitro and in vivo stability of liposomes loaded with calcitonin or indium in the gastrointestinal tract.

Factors affecting liposome transport to the blood compartment after oral administration to rats were evaluated. A high entrapment of calcitonin (CT) was obtained when the vesicles were prepared by sonication and were composed of egg phosphatidylcholine, cholesterol and stearylamine. In vitro tests showed that the liposomes were stable in light acidic or basic buffers, but that they were partly lysed in pH 2.5, 10 mM bile salts and pancreatin. Oral administration of liposomes entrapping calcitonin in fasting rats showed that the vesicles facilitate transport of the hormone to the general circulation and that they increase the lifetime of 125I-CT in blood. Oral administration of liposomes entrapping radioactive indium in fasting rats did not induce radioactivity in blood. This could be explained by disruption of most of the vesicles in the enterocytes.