Characterization of the structure of drug dispersions in polyethylene glycols using low-frequency dielectric spectroscopy

Abstract

Dispersions of a model drug, nortriptyline HCl, in polyethylene glycols 3400, 6000, 10 000 and 20 000 have been studied in both the molten and solid states using low-frequency dielectric spectroscopy. The molten response corresponded to a Maxwell-Wagner system, with a high-frequency conductance in series with a low-frequency barrier-layer capacitance. In comparison to the pure polymers, an increase in conductance was seen on addition of the drug to PEGs 6000 and 10 000, while little change was seen on addition to PEGs 3400 and 20 000. On solidifying the dispersions, the spectra showed a quasi-d.c. response which was associated with the distribution of the amorphous fraction within the sample. These studies indicate that the effect of additive inclusion on the structure of polymeric samples may be usefully examined over the low-frequency dielectric region.