Nanoparticle formulations as recrystallization inhibitors in transdermal patches

Drug crystallization in transdermal patches is still a major challenge, confronting the formulation development of topical drug delivery systems. Encapsulation of drugs into nanoparticles is proposed here as a promising tool for regulating drug crystallization in transdermal patches. The degree of recrystallization and transdermal permeation of ibuprofen and hydrocortisone loaded in polymeric and lipid nanoparticles from matrix-type transdermal patches were investigated. Ethyl cellulose (EC4), poly (lactide-co-glycolic acid) (PLGA) and polycaprolactone (PCL) were employed for polymeric nanoparticle preparations; while medium chain triglyceride (MCT) and witepsol were used for the preparation of MCT nanoemulsion and solid lipid nanoparticles (SLNs), respectively. As control, similar patches were prepared containing the free form of the investigated model drugs. All nanoparticle-containing transdermal patches exhibited less degree of drug recrystallization after 4 weeks compared to the control groups. Among the investigated nanocarriers, transdermal patches formulated with drug-loaded lipid nanoparticles showed the lowermost degree of recrystallization. Drug encapsulation into SLNs succeeded to reduce the degree of ibuprofen and hydrocortisone recrystallization from 23.3 +/- 0.9 and 21.9 +/- 1.2% to 0.2 +/- 0.1 and 1.8 +/- 0.1%, respectively. Additionally, the decreased crystalline fraction was accompanied by a corresponding increase in the drug flux through excised pig skin, which was found to be correlated to the hydrophobicity of the different nanocarriers. In conclusion, polymeric and lipid nanoparticles proved to be effective tools for the preparation of transdermal patches with on-demand drug loadings, while lowering the recrystallization risks. Moreover, the results of this study can be a valuable guidance for the design of effective transdermal patches by controlling the crystallization of various drugs through fine tuning of the carrier hydrophobicity.