Liposomes as a carrier for gentamicin delivery: development and evaluation of the physicochemical properties.

The physicochemical properties of liposomal formulations containing gentamicin were investigated. A sustained release of gentamicin from liposomes was observed at both 4 degrees C and 37 degrees C in phosphate buffered saline. The distribution of the mean diameters of these liposomal formulations, evaluated by dynamic light scattering (DLS) over a 48h time period, was bimodal with large polydispersity index values, i.e., > or =0.6. Incorporation of 5- or 16-doxylstearic acids (5- or 16-DSL) into the liposomes allowed the use of EPR spectroscopy to study the fluidity, order parameter, and phase behavior of the phospholipid bilayers in response to the compositions, temperature and time. While, our results revealed that gentamicin disturbs the packing and fluidizes the phospholipid chains, it did not seem to alter the nature of the microdomains at the polar interface of the bilayers. Simulation of the EPR spectra of 5-DSL containing liposomes revealed (1) the heterogeneous nature of the liposomal domains at the polar interfacial region, and (2) that encapsulation of gentamicin neither significantly alters the dynamic properties of the existing domains, nor induces the phase repartition of the liposomes within a 48h time course.