Exploring the effect of rheological modifiers and preservatives on the in vitro release of caffeine from gel formulations

It is known that diffusion and partition are the two most important phenomena in the complex process of skin penetration. To start this process, however, the active ingredient has to be released, i.e. it has to diffuse through the formulation and reach the stratum corneum in sufficient quantity. In this study, we have explored two formulation parameters that may influence the diffusion of caffeine through the hydrogel system: the type of gelling agent and the presence of preservative system. The aim was to assess whether and to which extent the changes in rheological properties exerted by the above two parameters affect the in vitro release of caffeine from the hydrogels.