Encapsulation of ampicillin in reverse-phase evaporation liposomes: a direct evaluation by derivative spectrophotometry

Ampicillin has been entrapped in phospholipid vesicles by reverse-phase evaporation technique. The relationship between lipid composition and the encapsulation efficiency or the release of ampicillin-loaded liposomes was studied in vitro using a derivative spectrophotometry assay. The encapsulation degree was closely dependent on the lipid mixture used in liposome preparation: in particular, phosphatidylcholine (DPPC) vesicles containing cholesterol (CHO) or lipopolysaccharide (LPS) had a lower entrapment efficiency than liposomes prepared with DPPC alone, whereas the presence of cardiolipin (CD conferred an opposite trend. From the release kinetics it appeared that vesicles leaked the carried drug by a biphasic feature both dialyzing against buffer or in bulk solution. These observations indicate that for the in vivo use of ampicillin-loaded liposomes as chemotherapeutic agents one must pay attention to the lipid composition of the vesicle, in order to modulate the dose-response effect. © 1991.