Critical role of water diffusion into matrix in external use iodine preparations

Iodine preparations for external use are recommended for treating pressure ulcers with manifestations of infection and necrosis. These ulcers abundantly produce wound exudates, which could be absorbed by water-soluble base. In this study we aimed to improve the previously reported methodologies for water absorption and new methodologies were developed in Franz diffusion cell with 100kDa molecular weight cut-off (MWCO) membranes. Using these new methodologies water absorbing capacities of existing iodine preparations [povidone-iodine (PI) sugar ointment, iodine-potassium iodide (IKI) gel, cadexomer-iodine (CI) ointment] and another superabsorbent polymer dextranomer paste were evaluated. Water absorption indexes were 7.52, 1.98, 1.44 and 2.90(mg/cm(2)/min(0.5)), respectively. With PI sugar ointment observed amount of water absorbed increased in a linear fashion over time. In contrast, with IKI gel, CI ointment and dextranomer paste observed amount of water absorbed decreased over time. When the observed amount of water absorbed was plotted against square of time, the lines of IKI gel and CI ointment became linear. With dextranomer paste the line became biphasic with 1-folding point. These results suggest that water diffusion into matrix is the rate limiting step in IKI gel, CI ointment and dextranomer paste, and that capacity of absorbing wound exudates could substantially differ among these ointments.