Nanosuspension technology is a strategy to increase the bioavailability of poorly soluble drugs and has been used for various routes of drug administration. Nanocrystals consist of pure drug, thus allowing the administration of a high drug dose in a small volume. This is advantageous for topical administration to increase the concentration gradient for the drug uptake into the skin. Moreover, the nm size of the drug (< 1μm) allows improved skin penetration and enhanced drug delivery to the target site. Nanosuspensions can be used as prepared or be loaded into semisolid vehicles. There are some challenges, which need to be solved. Stabilizers are unavoidable for aqueous nanosuspensions. However, stabilizers can also be a limiting factor for stability, e.g., during freeze-thaw cycling or sterilization. In addition, stabilizers might interact with the excipient in semisolid dosage forms, resulting in a different performance of the nanocrystals. The nanocrystal stability upon topical administration is also still an open question. Therefore, a systematic investigation of nanocrystal-loaded topical formulations was performed upon preparation, incorporation into semisolid vehicles and administration.
