(T1330-09-61) Hollow Microneedle-Based Delivery of Voriconazole Ionic Liquid for Nail Fungal Infections

Purpose: Onychomycosis, a persistent fungal infection of the nail, poses a significant therapeutic challenge due to the dense keratin structure of the nail plate and limited drug permeability [1]. Conventional topical treatments often fail to deliver adequate drug concentrations to the site of infection, while systemic therapies may cause adverse effects. Ionic liquids, particularly choline-geranic acid (CAGE), have emerged as novel, biocompatible solvents capable of enhancing drug solubility and transdermal delivery [2]. In this study, CAGE was synthesised using choline bicarbonate and geranic acid. Voriconazole (VCZ), a broad-spectrum antifungal agent, was incorporated into CAGE and delivered using hollow microneedles (MNs) to bypass the nail barrier and enable targeted drug delivery. The objective was to evaluate the solubility, syringeability, ex vivo skin permeation and antifungal efficacy of the VCZ-loaded CAGE MN system for potential use in the treatment of onychomycosis.

Methods: To synthesis the CAGE, choline bicarbonate and geranic acid were reacted in a 1:2, 1:3 and 1:4 molar ratio (Figure 1). Briefly, 80% w/w choline bicarbonate aqueous solution, 85% w/w geranic acid and methanol were added in a volumetric flask. The mixture was magnetically stirred at room temperature overnight, during which carbon dioxide gas was released as a byproduct. After the reaction was completed, the mixture was subjected to rotary evaporation under reduced pressure at 60 °C for 20 min. The completion of the reaction and the purity of CAGE were confirmed by ¹H NMR. The solubility of the drug in CAGE was determined by adding an excess amount of VCZ to CAGE and analysed using HPLC. Syringeability was assessed using a Texture Analyser by measuring the break loose force and glide force required to expel the formulation through the hollow MN. The ex vivo permeation profiles of the VCZ-loaded CAGE hollow MNs were evaluated via a Franz cell apparatus using full-thickness skin. The antifungal activity of the VCZ-loaded CAGE against Candida albicans ATCC 18804 was evaluated using a modified Kirby–Bauer disk diffusion method.

Results: The completion of the reaction and the purity of CAGE were confirmed by ¹H NMR (Figure 2a-c). The solubility of VCZ in different solvents, including water, PBS, and CAGE at varying molar ratios, was evaluated. As shown in Figure 2d, significantly enhanced solubility was observed in all CAGE formulations compared to water and PBS. The solubility increased with the geranic acid ratio 1:2, 1:3, and 1:4 exhibited highest solubilities of 13.27 ± 0.09 mg/g. The syringeability of hollow MNs loaded with different CAGE formulations was evaluated by measuring the force–distance profile and calculating the break loose force and glide force. As shown in Figure 2e, CAGE 1:2 required the highest injection force, while CAGE 1:4 showed the lowest break loose and glide forces, indicating improved flowability with higher geranic acid content. The ex vivo permeation of VCZ from different CAGE-loaded formulations was evaluated using Franz diffusion cells with porcine skin. The intradermal injection of MNs was visually confirmed by light microscopy and OCT (Figure 2f-g). As shown in Figure 2h, CAGE 1:4 loaded hollow MNs demonstrated the highest cumulative permeation at 80.66 ± 12.58 μg with 87.23 ± 13.60 % drug permeation over 24 h among all the formulation, indicating that increased geranic acid content improved skin penetration. The antifungal efficacy of the VCZ-loaded CAGE was evaluated against C. albicans. As illustrated in Figure 2i-j, the zone of inhibition (ZOI) produced by the VCZ-loaded CAGE was significantly larger than all other groups (p < 0.0001), indicating the greatest antifungal activity. Notably, the blank CAGE exhibited a measurable but smaller ZOI.

Conclusion: CAGE ionic liquids were successfully synthesised using choline bicarbonate and geranic acid at varying molar ratios (1:2, 1:3, and 1:4), with reaction completion confirmed by ¹H NMR. Among all formulations, CAGE 1:4 demonstrated the most favourable characteristics, including the highest solubility of VCZ, improved syringeability, and superior skin permeation through hollow MNs. Furthermore, the VCZ-loaded CAGE 1:4 exhibited the strongest antifungal activity against Candida albicans, indicating enhanced therapeutic potential. These findings suggest that CAGE-based ionic liquids, particularly at higher geranic acid ratios, are promising carriers for transdermal antifungal drug delivery using hollow MNs.

References: 1. Vikas, A., et al., Mechanistic insights of formulation approaches for the treatment of nail infection: conventional and novel drug delivery approaches. AAPS PharmSciTech, 2020. 21: p. 1-12.
2. Mitragotri, S., Choline geranate (CAGE): A multifaceted ionic liquid for drug delivery. Journal of Controlled Release, 2024. 376: p. 593-600.

Figure 1. A schematic representation of CAGE ionic liquid preparation.

Figure 2. ¹H NMR image of (a) CAGE 1:2, (b) CAGE 1:3, (c) CAGE 1:4; (d) solubility of VCZ in various solvent (means ± S.D., n = 3); (e) syringeability of hollow MNs loaded formulations (means ± S.D., n = 3); (f) drug depot on porcine skin after MN application under the digital microscopy; (g) representative cross-sectional OCT images of the drug depot formed in porcine skin after hollow microneedle insertion; (h) ex vivo permeation profiles (means ± S.D., n = 3); (i) photographic images of ZOI, petri dish diameter: 9 cm; (j) antifungal activity against C. albicans , represent the ZOI (mean ± SD, n = 4).