Ion Pair Strategy in Solid Lipid Nanoparticles: a Targeted Approach to Improve Epidermal Targeting with Controlled Adapalene Release, Resulting Reduced Skin Irritation.

PURPOSE Adapalene (AD) is one of the main retinoids used in the topical therapy of acne, an extremely common skin disease usually associated with psychological morbidity. However, like other retinoids, AD is frequently associated with skin irritation. To overcome the skin irritation, we proposed the encapsulation of AD in solid lipid nanoparticles (SLNs) using the ion pair strategy. METHODS The developed SLN-AD was characterized by high-performance liquid chromatography, differential scanning calorimetry, X-ray diffraction, synchrotron small-angle X-ray scattering, and transmission electron microscopy. In vitro permeation tests using porcine skin and in vivo mice skin irritation test were performed to evaluate, respectively, the drug's skin distribution and the skin irritation. RESULTS The characterization studies were able to demonstrate that the proposed strategy effectively provided high AD encapsulation in SLNs and its incorporation into a hydrophilic gel. Sustained release, epidermal targeting, and less skin irritation were observed for SLN-AD gel in comparison to the marketed AD gel. CONCLUSIONS The studies demonstrated that the encapsulation of AD in SLNs through the formation of an ion pair is a valuable alternative to diminish the adverse skin reactions caused by AD and can optimize patient adherence to treatment.