Single layer transdermal film containing lidocaine: water and lidocaine mobility determined using neutron scattering

The diffusivity of lidocaine through a polymer film developed for transdermal drug administration has been characterized by macroscopic permeation experiments and by neutron quasielastic spectroscopy that provides information on microscopic diffusivity parameters. It turns out that film hydration plays a key role on the performance and efficiency of the investigated system. Diffusion of lidocaine, at the microscopic level, is triggered by the presence of "mobile water." At hydration levels below 15% (weight water/weight hydrated film) neither lidocaine nor water show any appreciable long-range diffusion. At higher hydration levels, the onset of water long-range diffusion triggers diffusion of lidocaine through the film. The use of neutron quasielastic scattering makes it possible to measure lidocaine mobility within the film without the need of any additional physical barrier.