Formulation, in vitro release and transdermal diffusion of selected retinoids

Abstract

Acne is a multifactorial skin disease affecting about 80 % of people aged 11 to 30. Several systemic and topical treatments are used to treat existing lesions, prevent scarring and suppress the development of new lesions. Topical therapy is often used as first line treatment for acne, due to the location of the target organ, the pilosebaceous unit, in the skin. Retinoids are widely used as oral or topical treatment for this disease, with tretinoin and adapalene being two of the most used topical retinoids. The transdermal route offers several challenges to drug delivery, e.g. the excellent resistance of the stratum corneum to diffusion, as well as variable skin properties such as site, age, race and disease. Some additional difficulties are associated with the dermatological delivery of tretinoin and adapalene, which include suboptimal water solubility of the retinoids, isomerisation of tretinoin in the skin, mild to severe skin irritation, as well as oxidation and photo–isomerisation of tretinoin, even before crossing the stratum corneum. Researchers constantly strive to improve dermatological retinoid formulations in order to combat low dermal flux, skin irritation and instability. The release kinetics of tretinoin varies greatly according to the way in which it is incorporated into the formulation and according to the type of formulation used. Little research has been conducted regarding improved formulations for adapalene. Pheroid technology is a patented delivery system employed in this study in order to improve the dermal delivery of retinoids. Tretinoin and adapalene were separately incorporated into castor oil, vitamin F and Pheroid creams. The creams were evaluated in terms of their in vitro retinoid release, in vitro transdermal diffusion and stability. Castor oil and Pheroid creams were superior in terms of release and dermal delivery of adapalene. Tretinoin was best released and delivered to the dermis by castor oil cream. The castor oil creams were the most stable formulations, whereas the Pheroid creams were the most unstable. In terms of release, dermal diffusion and stability, castor oil cream proved to be the most suitable cream for both tretinoin and adapalene.