Abstract: Aim To evaluate liposome as an injectable delivery system of proteins, insulin was chosen as model drug and the hypoglycemic effect of PEG-coated liposomal insulin was tested. Methods The PEG-coated liposomal insulin was prepared by reversal-phase emulsion evaporation.For pharmacodynamic study, insulin (2.5 IU·kg^-1) was intravenously administered in phosphated-buffered saline (PBS) solution, conventional liposomes, and PEG-coated liposomes, separately, to normal Wistar rats.Blood glucose levels were determined by the glucose oxidase method. Results The mean diameter of the PEG-coated liposomal insulin was 58.4 nm, while the encapsulation ratio reached 18.33%.After intravenous administration of insulin solution, insulin liposome, and PEG-coated liposomal insulin, the minimum blood glucose concentrations (Cmin %) reached 25.26±5.75%, 33.92±12.42%, and 42.39±10.5% of the initial level, respectively, and the time periods to reach the minimum blood glucose level (Tmin) were 0.7±0.3 h, 1.2±0.4 h, and 2.3±0.7 h, respectively.The relative pharmacological bioavailabilities of insulin liposome and PEG-coated liposomal insulin were 98.03% and 99.70%, respectively, compared with the control of insulin solution. Conclusion PEG-coated liposome can be developed as a relatively sustained injectable delivery system for insulin. Moreover, the liposome coated with PEG may have advantages over normal liposome.

Key words: insulin, insulin, polyethylene glycol-coated liposome, polyethylene glycol-coated liposome, pharmacodynamics, pharmacodynamics