Comparative evaluation of the Munt-Dash air-interface diffusion chamber and Franz chamber for the in vitro examination of topical spray formulations

In vitro diffusion testing of topical formulations has long been examined using Franz diffusion chambers, however, Franz chambers are typically used with relatively large volumes, lack the air/membrane interface present in vivo, and do not account for changes in formula characteristics as solvent evaporates. Here we present our patented Munt-Dash diffusion chamber designed for direct spray application onto a model membrane. Diffusion characteristics from topical spray formulations utilizing both the Munt-Dash chamber and Franz diffusion chambers were evaluated and compared. Using diclofenac sodium and lidocaine hydrochloride as model drugs and shed snakeskin as a model for stratum corneum, test solutions were applied to Franz diffusion chambers using a pipette and to the Munt-Dash chamber using a high-speed syringe pump and sprayer. Both chambers presented permeability data consistent with previously reported in vitro and in vivo studies. Significant differences were observed in permeability by formulation and temperature. This suggests that although Franz chambers produce relevant data, the failure to account for small volumes and drying during application may produce misleading results. The Munt-Dash chamber may improve in vitro testing by providing these factors. This data suggests the Munt-Dash chamber is a suitable alternative to the Franz chamber for topical spray formulations.