Abstract. The aim of the present investigation was to evaluate microemulsion as a vehicle for dermal drug delivery and to develop microemulsion-based gel of terbinafine for the treatment of onychomycosis. Doptimal mixture experimental design was adopted to optimize the amount of oil (X 1 ), Smix (mixture of surfactant and cosurfactant; X 2 ) and water (X 3 ) in the microemulsion. The formulations were assessed for globule size (in nanometers; Y 1 ) and solubility of drug in microemulsion (in milligrams per milliliter; Y 2 ). The microemulsion containing 5.75% oil, 53.75% surfactant-cosurfactant mixture and 40.5% water was selected as the optimized batch. The globule size and solubility of the optimized batch were 18.14 nm and 43.71 mg/ml, respectively. Transmission electron microscopy showed that globules were spherical in shape. Drug containing microemulsion was converted into gel employing 0.75% w/w carbopol 934P. The optimized gel showed better penetration and retention in the human cadaver skin as compared to the commercial cream. The cumulative amount of terbinafine permeated after 12 h was 244.65±18.43 μg cm −2 which was three times more than the selected commercial cream. Terbinafine microemulsion in the gel form showed better activity against Candida albicans and Trichophyton rubrum than the commercial cream. It was concluded that drug-loaded gel could be a promising formulation for effective treatment of onychomycosis.

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Onychomycosis is one of the most common nail disorders. It affects 10-30% of the world population and is caused by dermatophytes, non-dermatophytes, molds, and yeasts. Present treatment methods of onychomycosis include oral therapy, topical therapy, and a combination of both; they have mild-to-moderate efficacy, with a relapse and reinfection rate of 20-25%. For oral therapy, newer antifungal compounds (azole class and allylamine class) are being investigated to increase efficacy and minimize side effects. Oral therapy with antifungal agents have severe side effects, with lesser bioavailability and longer duration of treatment. By contrast, topical therapy of onychomycosis is associated with greater patient compliance and fewer systemic side effects and drug interactions. Current topical treatment options of onychomycosis are nail lacquers, ointments, lotions, solutions, and gels, but these formulations have been unsuccessful due to poor penetration and distribution of drugs at the infected site. Therefore, novel therapeutic options are constantly being researched to improve the efficacy of onychomycosis treatment by enhancing the permeation of the drug across the nail to reach the infected site. Various physical and chemical enhancement methods have been studied to increase the permeation of drugs across the nail plate to the nail bed. Device-based therapeutic options have also been investigated to increase the antifungal drug concentration and its effects in the onychomycotic nail. Randomized clinical trials of these novel therapies have demonstrated better efficacy. The present review discusses the anatomy of the human nail, onychomycosis and its types, onycholysis, and conventional and novel therapies. We also review patents granted as well as design challenges facing optimal drug formulation for onychomycosis treatment.

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