Retardation of Dermal Release by Film Forming Emulsions

Abstract

The therapy of chronic skin diseases often requires multiple applications of creams or ointments per day over a long period of time. As patient compliance decreases with an increasing number of daily doses, several attempts have been made to achieve sustained dermal release. The employed formulations are either semisolids which deliver the api rapidly to the skin and lead to the built-up of a reservoir in stratum corneum. From this reservoir, the api is released to deeper skin layers over a certain period of time. On the other hand, patches are available. They themselves represent a reservoir for the active and control the release rate. However, both formulation concepts exhibit disadvantages. Semisolids do not show the required substantivity to keep the api in contact with the skin over the requested time. With patches, the area which may be treated is limited by the size of the patch. And optimally designed formulation would therefore permit sustained release of the api, be easy to spread and show the required substantivity. These criteria are met by film forming emulsions. Film forming emulsions are oil-in-water emulsions that contain a lipophilic api (nonivamide, in our study) in the inner oil phase of the emulsion. The continuous aqueous phase comprises the dispersions of sustained release polymers (namely Eudragit ® NE and Eudragit ® RS) which enable film formation on the skin. In this film, the oil droplets are embedded in a polymeric matrix which acts as a diffusion barrier for the api and therefore sustains its release from the oil droplets to the skin. Thus, constant permeation rates over a period of 12–24 h may be achieved and the application frequency may thereby be reduced to a once or twice daily application. This is a clear advantage over conventional formulations which have to be applied up to six times per day. It results in enhanced compliance and ensures therapeutic success. Thereby, film forming emulsions close a therapeutic gap in the treatment of chronic skin diseases.