Characteristics of Hydrogels as a Coating for Microneedle Transdermal Delivery Systems with Agomelatine

Agomelatine (AGM) is an effective antidepressant with low oral bioavailability due to intensive hepatic metabolism. Transdermal administration of agomelatine may increase its bioavailability and reduce the doses necessary for therapeutic effects. However, transdermal delivery requires crossing the stratum corneum barrier. For this purpose, the use of microneedles may increase the efficiency of administration. The aim of this study was to prepare an agomelatine-loaded hydrogel suitable for coating microneedles for the transdermal drug delivery of AGM. The optimized formulations were subjected to spectroscopic and rheological characterization and mechanical tests, as well as tested for release through an artificial membrane and permeation through human skin ex vivo. Both hydrogels were found to have suitable parameters for coating microneedles using the dip-coating method, including the stability of the substance at the process temperature, shear-thinning behavior, and appropriate textural parameters such as adhesion or hardness. Additionally, two formulations were tested for potential application to the skin alone because the gels showed suitable mechanical properties for the skin application. In this case, the ethanol gel was characterized by higher skin permeability and better spreadability. The information obtained in this study will allow the preparation of coated microneedles for the transdermal administration of agomelatine.