**1. Introduction**

Oral candidiasis is a frequently encountered infection of the oral mucosa. It can be caused by the overgrowth of 150 species of *Candida*; however, 95% cases are caused by *Candida* albicans [1,2]. This is sometimes mild in nature, but may be resistant to therapies and is frequently vulnerable to relapse.

The drug of choice for the treatment of oral candidiasis is fluconazole, a fluorinated bis-triazole derivative. This agent has been found to be effective against several species of *Candida* in both immunocompromised and immunocompetent patients [3]. The mechanism of inhibiting *Candida* spp. infection involves the inhibitory effect of 14-α-demethylase, which is required for ergosterol biosynthesis and thereby interrupts the cell wall synthesis of the fungi. The common route of administration of conventional fluconazole is oral; however, this route is known to produce gastrointestinal disturbances, such as abdominal discomfort, bloating, vomiting, and severe hepatotoxicity [4]. Localized delivery of the

**Citation:** Alkhalidi, H.M.; Hosny, K.M.; Rizg, W.Y. Oral Gel Loaded by Fluconazole-Sesame Oil Nanotransfersomes: Development, Optimization, and Assessment of Antifungal Activity. *Pharmaceutics* **2020**, *13*, 27 . https://doi.org/ 10.3390/pharmaceutics13010027

Received: 2 December 2020 Accepted: 22 December 2020 Published: 25 December 2020

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medication for the treatment of oral candidiasis could reduce the development of drug resistance and also reduce the associated side effects [3]. Conventional local forms of delivery of fluconazole (e.g., sprays, lotions, gels, and creams) are associated with major limitations in dosing accuracy and length of time at the site of application, as well as variations in performance. Lozenges, troches, rinses, and mouth paints are the alternate treatment options for oral candidiasis; however, maintenance of the salivary concentration of the medication is difficult because salivary secretions can wash away these substances and shorten the contact time of the formulation, leading to poor efficacy and poor patient compliance [4,5]. Therefore, novel formulations with properties that are retained at the site of application and release the entrapped drug for a desired period would be a possible alternative to conventional deliveries. Researchers have used various approaches to deliver fluconazole effectively and with improved efficacy. They used mucoadhesive platforms, such as fluconazole-loaded oral strips [3], mucoadhesive nanoparticles [4], hydrogels [6], and natural rubber latex biomembranes [7], among others.

In view of the advantages of longer retainment at the site of application for the mucoadhesive components and the superior release characteristics of the nanotechnology-based products, the present study aimed to formulate fluconazole-loaded sesame oil containing nanotransfersomes (FS-NTF) embedded in a cross-linked hyaluronic acid hydrogel. A new field of research on topical delivery was opened with the use of liposomes for dermal delivery, and since then, a wide range of novel lipid-based vesicles, such as deformable liposomes in nanosizes, which are currently known as nanotransfersomes, have been developed. The addition of nonionic surfactants to the liposomal bilayer structure of liposomes provides the flexibility necessary for liposomes, and this new structure is called the nanotransfersome [8]. In the proliferation phase, in which granulation tissue is formed, hyaluronic acid is synthesized mainly by fibroblasts, and this allows, within the framework of a temporary extracellular matrix, the diffusion of nutrients and the elimination of waste products. Hyaluronic acid facilitates the migration and proliferation of fibroblasts and keratinocytes and is a reservoir of growth factors. This is due to the ability of hyaluronic acid to absorb water, maintain wound moisture, and limit cellular adhesion to extracellular matrix molecules [9]. Hyaluronic acid has also been shown to possess antifungal efficacy, especially fungistatic efficacy [10]. Therefore, it was expected that superior efficacy would be achieved by the FS-NTF embedded in hyaluronic acid (HA-FS-NTF). It was expected that the formulation would remain at the site of application because of the swelling properties of hyaluronic acid [11]. Additionally, incorporation of sesame oil in the formulation would be advantageous for its established antifungal efficacy [12]. To reach this goal, the optimization of the FS-NTF was performed by the Box-Behnken statistical design to determine the various parameters that influence the vesicle size, entrapment efficiency, zone of inhibition, and ulcer index. Finally, the HA-FS-NTF was formulated and evaluated for its rheological behavior, in vitro release pattern, ex vivo permeability, inhibitory zone of *Candida* growth, and ulcer index in an immunocompromised animal model.
