(M1330-05-27) Design of Foamable Microemulsions for Vaginal Antifungal Drug Delivery

Purpose: Vulvovaginal candidiasis is a fungal disease that significantly affects the quality of life for women. Available treatments for local administration are usually long and uncomfortable, while oral therapy may lead to hepatotoxicity and systemic adverse effects. Microemulsions may be advantageous systems because they can enhance the solubility and permeation of active pharmaceutical ingredients. Furthermore, when properly formulated, microemulsions can be foamed. Foams are appealing for vaginal drug delivery as they do not leave stains or residues and can expand and cover body cavities. The purpose of this work was to design and characterize foamable microemulsions tailored for fluconazole intravaginal delivery.

Methods: Surfactants and oils were screened for solubilization ability of fluconazole by a saturation solubility study. An excess amount of fluconazole was added into a fixed amount of each vehicle and shaken (Shaker IKA Vibrax VXR) for 72 h at 25 °C at 200 rpm protected from the light. The mixture was centrifuged (accuSpin Micro 17, Fisherbrand) at 4000 x g for 30 min and the drug was quantified in the supernatant by UV-visible spectrophotometer at 260 nm. Microemulsions were prepared by adding oil and water directly to the previously mixture of surfactant and co-surfactant (S_mix) and vortexed for 1 min after each addition. Fluconazole (1% w/w) was added and sonicated in an ultrasonic bath until a clear microemulsion was formed. For foam production, microemulsions were loaded into propellent-free foam dispensers. To select the optimal proportions of surfactants and oil, a design of experiments (DoE) with surface response methodology was performed using Minitab Statistical Software. The input factors were percentage (w/w) of S_mix (ratio of 2:1) and percentage (w/w) of oil, varying at three levels (25 - 45% for S_mix and 0.5 - 3.5% for oil). A total of 14 formulas with 6 central points were prepared in randomized order. The critical quality attributes selected were droplet size and foam stability. Droplet size was measured by dynamic light scattering (DLS) using Zetasizer Ultra (Malvern Instruments) without dilution at 25°C in triplicates. Foam stability was measured in seconds for the foam to completely disappear after being dispensed until the 25 mL mark of a graduated cylinder. The optimal microemulsion composition was defined using the response optimizer tool from Minitab Statistical Software. Physical stability of optimal microemulsions was evaluated by centrifugation study using 8960× g for 30 min at 25°C and five repeated freeze-thawing cycles (−20°C for 48 h and 25°C for 4 h). After each cycle, the pH of microemulsions was analyzed by a digital pHmeter (Accumet XL20, Fisherbrand), as well as the droplet size and polydispersity index in the Zetasizer. Antifungal activity of the optimal formulations was investigated against Candida albicans ATCC 10231, using the broth microdilution method to determine the minimum inhibitory concentration (MIC).

Results: Based on higher solubility, the excipients selected for fluconazole microemulsion were Labrasol as the surfactant (59.2 ± 10.1 mg/mL), Transcutol as the co-surfactant (188 ± 7.4 mg/mL) and Capryol 90 as the oil (46.4 ± 6.7 mg/mL). Surfactant mix (S_mix) and oil percentages influenced the droplet size and foam stability through the design of experiments statistical approach. The droplet size could be predicted by the input factors in a quadratic polynomial model, while the foam stability could be predicted in a polynomial model. The contour and 3D surface response plots demonstrate that the foam stability increases with lower oil quantity, while the droplet size increases with higher oil and lower surfactant until a certain point, when their influence is inverted. The optimal composition was defined by the software as 16% of Labrasol, 8% of Transcutol, 0.5% of Capryol 90 and 74.5% of water, resulting in a microemulsion with size of 20 nm and higher foam stability ( > 800 seconds). No significant change (p > 0.05) on the droplet size, polydispersity index or pH of the optimized microemulsion could be detected after 5 cycles of freeze-thawing. Minimum inhibitory concentration of optimal microemulsion was 3.91 µg/mL against C. albicans.

Conclusion: Foamable microemulsions loaded with fluconazole were successfully prepared and characterized. Fluconazole microemulsion had satisfactory parameters of physical stability and antifungal activity. The statistical approach demonstrated that the microemulsion surfactant and oil percentage composition directly impacts the globule size and foam stability. The overall findings from this study contribute towards the development of an appropriate dosage form for treating vulvovaginal candidiasis and improving women's health and well-being.

References: HAJJAR, B. et al. In Vitro Evaluation of a Foamable Microemulsion Towards an Improved Topical Delivery of Diclofenac Sodium. AAPS PharmSciTech, 23, n. 4, p. 102, 2022.
YUKUYAMA, M. N. et al. Olive oil nanoemulsion preparation using high-pressure homogenization and d-phase emulsification – A design space approach. Journal of Drug Delivery Science and Technology, 49, p. 622-631, 2019.

Acknowledgements: This research was funded by grants #2021/00319-3, #2022/02120-2 and #2022/00931-3, São Paulo Research Foundation (FAPESP).


Saturation solubility of fluconazole in microemulsion excipients.


Contour plot and surface plot of the interaction between the output response, droplet size (nm), and the input factors, Smix (% w/w) and Oil (% w/w).


Contour plot and surface plot of the interaction between the output response (foam stability in seconds) and the input factors (Smix and Oil percentages).