Objective To optimize the formulation process of co-loaded nanoparticles (TBF-HQD-SAN NPs) comprising self-assembled nanoparticles of Huangqin Decoction (黄芩汤) (HQD-SAN) and terbinafine (TBF). Methods The HQD-SAN was obtained with high-speed centrifugation combined with dialysis and then TBF was further loaded to prepare TBF-HQD-SAN NPs. Based on the single-factor investigation, taking the concentration of HQD-SAN, the speed of magnetic stirring and the stirring time as the investigation factors, and the drug loading (DL) of TBF, the encapsulation efficiency and the DL of baicalin as the investigation indicators, the formulation and process of TBF-HQD-SAN NPs were optimized by using the 3-factor 3-level Box-Behnken design (BBD)-response surface methodology (RSM). The optimized TBF-HQD-SAN NPs were characterized for morphology, particle size distribution, ζ potential, and drug-loading capacity. Their saturated solubility was determined, and their antifungal activity against Trichophyton rubrum, T. mentagrophytes, and Microsporum canis was investigated. Results The TBF-HQD-SAN NPs process was optimized by BBD. The established quadratic regression model had excellent fit (all R² > 0.99), and the concentration of HQD-SAN, stirring speed, stirring time and some interaction terms had significant effects on the indicators (P < 0.05). The effect surface analysis showed that the drug loading of TBF decreased with the increase of HQD-SAN concentration and first increased and then decreased with the stirring speed/time. The encapsulation rate/drug loading of baicalin increases with the increased of HQD-SAN concentration and decreased with the extension of stirring speed/time. The optimal process for model selection was as follows: HQD-SAN concentration 5.6 mg/mL, TBF 5 mg, distilled water 4 mL, ultrasonic (50 W, 40 kHz) for 30 min, magnetic stirring at 760 r/min for 1.5 h, and filtration through 0.8 μm filter membrane. The measured values of each index in the verification experiment were close to the predicted values (RSD < 5%). The particle size of the NPs was (185.10 ± 1.73) nm, the polydispersity index (PDI) was 0.22 ± 0.01, and the ζ potential was (−15.17 ± 1.40) mV. The encapsulation efficiency and DL of TBF were (99.81 ± 0.33)% and (3.32 ± 0.09)%, respectively, while those of baicalin were (58.59 ± 1.42)% and (6.71 ± 0.15)%, respectively. The equilibrium solubility was (2.27 ± 0.09) μg/mL for TBF alone, (15.70 ± 1.66) μg/mL for the TBF-HQD-SAN physical mixture (PM), and (78.20 ± 2.22) μg/mL for the TBF-HQD-SAN NPs. The antifungal experiment showed that the antifungal activity of TBF-HQD-SAN NPs (with MIC values ranging from 0.15—0.31 µg/mL, equivalent to 4.98—10.13 ng/mL based on TBF content) was significantly superior to that of HQD-SAN (MIC value 1.56—3.13 mg/mL) and TBF alone (MIC value 0.06—0.50 µg/mL) (P < 0.05). Conclusion The BBD successfully optimized the formulation and preparation process of TBF-HQD-SAN NPs. The resulting NPs demonstrated uniform particle size, excellent drug-loading performance, and significantly enhanced antifungal efficacy, laying a foundation for further research.

Huangqin Decoction  /  self-assembled nanoparticles  /  terbinafine  /  co-loaded nanoparticles  /  baicalin  /  Box-Behnken design-response surface method  /  anti-dermatophyte