Raman Microspectroscopy as a Tool to Elucidate the Efficacy of Topical Formulations Containing Curcumin.

The success of the onychomycosis treatment is directly associated with factors such as the choice of the medication, the administration route, and the pharmaceutical formulation. Photodynamic therapy (PDT) is an emerging and promising technique indicated for onychomycosis treatment. For this application, the main challenge is the efficient delivery of the photosensitizer (PS). Curcumin is widely used as a PS, however it is an unstable molecule and it is a challenge to develop a formulation with good penetration into the nail plate, maintaining the stability of curcumin. In this study, the molecular mechanisms underlying the efficacy of two topical formulations containing curcumin used in a clinical trial for onychomycosis treatment were analyzed by Raman microspectroscopy. It is shown that curcumin is present in both formulations in aggregated and non-aggregated states, and in aggregates it is present in different conformations, depending on the interaction with the solvent. This proves to be critical for efficient and uniform PS delivery to the nail and its complete use during the treatment. These analyses are showing how promising Raman microspectroscopy is in understanding the molecular mechanisms of the efficiency of photosensitizers and are helping to improve the development of pharmaceutical formulations.