Development and Evaluation of Organic Acid-Based Hydrogels for Antifungal Treatment of Companion Animal Dermatomycoses: A One Health Perspective

Introduction

Dermatophytosis caused by Microsporum canis is a common zoonotic skin infection in pets, often requiring prolonged treatment due to persistence in keratinized tissues. Its zoonotic nature highlights its importance within the One Health framework, as infected animals may contribute to transmission to humans. Organic acids represent promising antifungal agents due to their biocompatibility and mechanisms of action. Hydrogel systems may enhance topical drug delivery by enabling controlled release and improved retention. This study aimed to evaluate the antifungal activity of selected organic acids and to assess the physicochemical and antifungal properties of acid-based hydrogel formulations.

Methods

Ethanol-based solutions of gallic, coumaric, ferulic, and cinnamic acids (0.31–5%) were tested against M. canis using the agar well diffusion method. Cinnamic acid demonstrated the highest antifungal efficacy, which led to its selection for incorporation (0.5%) into hydrogel formulations containing poloxamer 407 and hydroxyethylcellulose with varying polymer ratios. Hydrogels were characterized by pH measurement and rheological analysis. Antifungal activity was evaluated using the same diffusion method. In vitro release studies were performed using a modified Franz diffusion cell system.

Results

Cinnamic acid demonstrated the highest antifungal activity, with inhibition zones increasing from 35.6 ± 1.7 mm (0.31%) to 73.2 ± 13.8 mm (5%). All hydrogel formulations retained antifungal activity against M. canis, producing ~17 mm inhibition zones, indicating diffusion limitations within the polymer matrix. Rheological analysis showed formulation-dependent viscosity (73.1–311.5 Pa·s at 35 °C), and all hydrogels had slightly acidic pH (4.81–4.92). In vitro, 34.8 ± 3.3% of cinnamic acid was released over 5 hours, suggesting a diffusion-controlled release profile.

Conclusions

Cinnamic acid demonstrated strong antifungal activity and retained its efficacy when incorporated into hydrogel systems, enabling controlled release. These findings indicate that cinnamic acid is a promising candidate for topical antifungal therapy, while poloxamer 407/hydroxyethylcellulose hydrogels may serve as a platform for prolonged local antifungal drug delivery.