Results from a Phase 1/2 trial of BB2603, a terbinafine-based topical nano-formulation, in onychomycosis and tinea pedis.

BB2603 is a nano-formulation of the antifungal drug terbinafine with the polymer polyhexamethylene biguanide (PHMB) as an excipient to enhance solubility and drug delivery to skin and nails. BB2603 is delivered topically using a low-velocity spray. It is being developed in different strength formulations for the treatment of fungal infections of the nail and skin, including onychomycosis and tinea pedis, with BB2603-1 (0.01% terbinafine) tested in the present trial. The aim of this study was to assess systemic exposure, safety and tolerability of BB2603-1 compared with Lamisil® AT 1% spray and BB2603-1 vehicle control in onychomycosis and tinea pedis. Preliminary mycological and clinical activity were also investigated. This was a single-centre Phase 1/2, randomised, partially blinded, active- and vehicle-controlled, parallel-group trial in 46 subjects with onychomycosis associated with tinea pedis. Part 1 investigated BB2603-1 versus Lamisil AT 1% spray and BB2603-1 vehicle (4 weeks treatment). Part 2 investigated BB2603-1 versus BB2603-1 vehicle (additional 48 weeks treatment). No measurable systemic exposure of terbinafine was shown over 52 weeks of treatment with BB2603-1. BB2603-1 had an excellent safety and tolerability profile with no drug-related safety findings and no evidence of skin sensitisation. BB2603-1 showed preliminary evidence of anti-dermatophyte activity, demonstrated by a reduction in dermatophyte positive cultures and a reduction in microscopic evidence of dermatophytes. The pharmacokinetic, safety and efficacy data from this trial support further development of the topical terbinafine-based nano-formulation BB2603 in fungal infections of the skin and nail, including onychomycosis and tinea pedis.

Assessment of the nail penetration of antifungal agents, with different physico-chemical properties.

Onychomycosis, or fungal nail infection, is a common fungal infection largely caused by dermatophyte fungi, such as Trichophyton rubrum or Trichophyton mentagrophytes, which affects a significant number of people. Treatment is either through oral antifungal medicines, which are efficacious but have significant safety concerns, or with topical antifungal treatments that require long treatment regimens and have only limited efficacy. Thus, an efficacious topical therapy remains an unmet medical need. Among the barriers to topical delivery through the nail are the physico-chemical properties of the antifungal drugs. Here, we explore the ability of a range of antifungal compounds with different hydrophilicities to penetrate the nail. Human nail discs were clamped within static diffusion (Franz) cells and dosed with equimolar concentrations of antifungal drugs. Using LC-MS/MS we quantified the amount of drug that passed through the nail disc and that which remained associated with the nail. Our data identified increased drug flux through the nail for the more hydrophilic compounds (caffeine as a hydrophilic control and fluconazole, with LogP -0.07 and 0.5, respectively), while less hydrophilic efinaconazole, amorolfine and terbinafine (LogP 2.7, 5.6 and 5.9 respectively) had much lower flux through the nail. On the other hand, hydrophilicity alone did not account for the amount of drug associated with/bound to the nail itself. While there are other factors that are likely to combine to dictate nail penetration, this work supports earlier studies that implicate compound hydrophilicity as a critical factor for nail penetration.