AimTo evaluate liposome as an injectable del iv ery system of proteins, insulin was chosen as model drug and the hypoglycemic
ef fect of PEG-coated
liposomal insulin was tested. Methods The PEG-coated liposomal insulin was prepared by reversal-phase emulsion eva po ration. For pharmacodynamic study, insulin (2 5 IU·kg -1 ) was
intravenous ly administered in phosphated-buffered saline (PBS) solution, conventional lipo somes, and PEG-coated liposomes, separately, to normal Wistar rats. Blood gluco se levels were determined by the glucose oxidase method. ResultsThe mean diameter of the PEG-coated liposomal insulin was 58.4 nm, wh ile the encapsulation ratio reached 18.33%. After intravenous administration of insulin solution, insulin liposome, and PEG-coated liposomal insulin, the minim u m blood glucose concentrations (C min %) reached 25.26±5.75%, 33.92±1 2.42%, and 42.39±10 5% of the initial level, respectively, and the time periods to reach the minimum blood glucose level (T min ) were 0 7±0 3 h, 1.2±0 4 h, and 2.3±0 7 h, respectively. The relative pharmacological bioavailabilities of insulin lipo some and PEG-coated liposomal insulin were 98.03% and 99.70%, respectively, com p ared with the control of insulin solution. ConclusionPEG -coated liposome can be developed as a relatively sustained injectable delivery system for insulin. Mor eover, the liposome coated with PEG may have advantages over normal liposome.