The measurement of beclomethasone dipropionate entrapment in liposomes: a comparison of a microscope and an HPLC method

The purpose of this study was to examine the methodologies that may be used to estimate the maximum incorporation (< 5 mole% drug) of beclomethasone dipropionate (BDP) in dipalmitoylphosphatidylcholine (DPPC) multilamellar liposomes. Two approaches are described. First, differential interference contrast (DIC) microscopy and cross-polarisation microscopy have been used to measure the concentration at which BDP crystals become apparent in BDP-containing liposome preparations, thereby allowing a semi-quantitative but simple estimation of entrapment. An alternative method is described whereby the unentrapped solid drug is separated from the liposomes via suspension in D2O followed by centrifugation and HPLC analysis. The method resulted in an estimate of 1.5-2 mole% BDP, while the HPLC method yielded a value of 2.52 mole% BDP. (C) 2001 Elsevier Science B.V. All rights reserved.