Validation of spectrophotometric methods for the simultaneous determination of fluconazole and riparin B in the development of lipid nanoparticles modified by β-cyclodextrin: Application for in vitro characterization and ex vivo studies of nail retention

Abstract

Fluconazole (FLC) has been used in the clinic for almost thirty years as a treatment for fungal infections, but its widespread use has led to the emergence of resistant strains. In this context, synthetic analogues of riparins, phytocompounds isolated from Aniba riparia (Nees) Mez (Lauraceae), such as Riparin B (RIP), stand out as an important agent for modulating antimicrobial resistance, potentially useful for treating superficial mycoses resistant to conventional antifungals. Onychomycosis is one of the main fungal infections affecting the nails. Its local treatment is desirable but has limited efficacy due to poor drug permeation. The use of nanoparticles and permeation promoters can increase permeability and improve treatment. Therefore, nanostructured lipid carriers coated with β-cyclodextrin (MNLC) were developed for the topical application of FLC and RIP on nails. To support the formulation, four spectrophotometric methods (amplitude factor, amplitude subtraction, modified amplitude subtraction, and fourth-order derivative), based on derivative spectroscopy and simple mathematical manipulations, were validated, in accordance with the International Conference on Harmonization (ICH), for simultaneous determination of FLC and RIP in the MNLC and in in vitro characterization studies of the formulation. In addition, the methods were applied to quantify drug retention in porcine hooves using an optimized extraction process. All the methods developed were found to be linear (r > 0.999), precise (RSD < 5 %), and accurate (92.33 to 108.86 %) without being affected by the components of the formulation or the biological matrix. The methods developed made it possible to determine the encapsulation efficiency and sustained release profile of the drugs. In addition, successive extractions revealed the amount of FLC and RIP retained in the superficial and deeper regions of porcine hooves. Thus, the results indicated that FLC and RIP can be determined simultaneously, quickly, simply, and economically, using any of the proposed methods, in complex MNLC samples and the biological matrix of porcine hooves.