Quantitative LC-MS determination of liposomal encapsulated prednisolone phosphate and non-encapsulated prednisolone concentrations in murine whole blood and liver tissue.

The underlying pharmacokinetic profile of liposomal drug delivery systems is not yet fully known. This is primarily due to a lack of suitable quantitative bioanalytical methodology to simultaneously determine separate liposomal-encapsulated and non-encapsulated drug tissue concentrations in complex biological samples. Here, an LC-MS method was developed which enables the simultaneous quantification of separate liposomal-encapsulated prednisolone phosphate and non-encapsulated prednisolone concentrations in whole blood and liver tissue. Liquid chromatography, negative electrospray ionization and Orbitrap-MS analysis allowed highly accurate and sensitive detection of prednisolone phosphate (PP) and prednisolone (P) in complex matrix. Using dexamethasone phosphate and dexamethasone as internal standards, the quantitative LC-MS method was optimized and validated for high selectivity, sensitivity and quantitative accuracy of PP and P from liposomes. The lower limits of quantitation were 0.99μmol/L blood and 0.53nmol/g liver for PP, and 229nmol/L blood and 0.514nmol/g liver for P. Quantitative accuracies of 84-118% were observed. The intra-run precision was ≤11%. Application of this new LC-MS method will yield the first liposomal pharmacokinetic profile showing accurate encapsulated and non-encapsulated drug tissue concentrations separately. This is also the first quantitative LC-MS method for the simultaneous quantification of the prodrug PP and its parent drug P in whole blood and liver tissue samples.