Investigation of factors affecting in vitro doxorubicin release from PEGylated liposomal doxorubicin for the development of in vitro release testing conditions. 
Establishing appropriate drug release testing methods of liposomal products for assuring quality and performance requires the determination of factors affecting in vitro drug release.  In this study, we investigated the effects of test conditions (human plasma lot, pH/salt concentration in the test media, dilution factor, temperature, ultrasound irradiation, etc.),  and liposomal preparation conditions (pH/concentration of ammonium sulfate solution), on doxorubicin (DXR) release from PEGylated liposomal DXR.  Higher temperature and lower pH significantly increased DXR release.  The evaluation of DXR solubility indicated that the high DXR release induced by low pH may be attributed to the high solubility of DXR at low pH. Ultrasound irradiation induced rapid DXR release in an amplitude-dependent manner.  The salt concentration in the test solution, human plasma lot, and dilution factor had a limited impact on DXR-release.  Variations in the ammonium sulfate concentration used in solutions for the formation/hydration of liposomes significantly affected DXR release behavior, whereas differences in pH did not.  In addition, heating condition in phosphate-buffered saline at lower pH (<6.5) exhibited higher discriminative ability for the release profiles from various liposomes with different concentrations of ammonium sulfate than did ultrasound irradiation.  These results are expected to be helpful in the process of establishing appropriate drug release testing methods for PEGylated liposomal DXR.