Abstract

Formulation effects on the entrapment of beclometasone dipropionate (BDP)
in liposomes generated by hydration of proliposomes were studied, using the high-density
dispersion medium deuterium oxide in comparison to deionized water (DW). Proliposomes
incorporating BDP (2 mol% of the lipid phase consisting of soya phosphatidylcholine (SPC)
and cholesterol; 1:1) were manufactured, using lactose monohydrate (LMH), sorbitol or Dmannitol
as carbohydrate carriers (1:5 w/w lipid to carrier). Following hydration of
proliposomes, separation of BDP-entrapped liposomes from the unentrapped (free) BDP
at an optimized centrifugation duration of 90 min and a centrifugation force of 15,500g were
identified. The dispersion medium was found to have a major influence on separation of
BDP-entrapped liposomes from the unentrapped drug. Entrapment efficiency values were
higher than 95% as estimated when DW was used. By contrast, the entrapment efficiency was
19.69 ± 5.88, 28.78 ± 4.69 and 34.84 ± 3.62% upon using D2O as a dispersion medium (for
LMH-, sorbitol- and D-mannitol-based proliposomes, respectively). The similarity in size of
liposomes and BDP crystals was found to be responsible for co-sedimentation of liposomes
and free BDP crystals upon centrifugation in DW, giving rise to the falsely high entrapment values estimated. This was remedied by the use of D2O as confirmed by light microscopy, nuclear magnetic resonance (1HNMR), X-ray diffraction (XRD) and entrapment studies. This study showed that carrier type has a significant influence on the entrapment of BDP in liposomes generated from proliposomes, and using D2O is essential for accurate determination of steroid entrapment in the vesicles.