Onychomycosis is a disease of the nail caused by yeast, dermatophytes, or other molds, and represents approximately 50% of all nail disorders. Toenail infection accounts for approximately 80% of onychomycosis incidence, while fingernails are affected in about 20% of the cases. Dermatophytes are the most frequent cause of nail plate invasion, particularly in toenail onychomycosis. Onychomycosis caused by a dermatophyte is termed tinea unguium. Trichophyton rubrum is by far the most frequently isolated dermatophyte, followed by T. mentagrophytes. Distal subungual onychomycosis is the most common presentation of tinea unguium, with the main site of entry through the hyponychium (the thickened epidermis underneath the free distal end of a nail) progressing in time to involve the nail bed and the nail plate. Discoloration, onycholysis, and accumulation of subungual debris and nail plate dystrophy characterize the disease. The disease adversely affects the quality of life of its victims, with subject complaints ranging from unsightly nails and discomfort with footwear, to more serious complications including secondary bacterial infections.
Many methods are known for the treatment of fungal infections, including the oral and topical use of antibiotics (e.g., nystatin and amphotericin B), imidazole anti-fungal agents such as miconazole, clotrimazole, fluconazole, econazole and sulconazole, and non-imidazole fungal agents such as the allylamine derivatives terbinafine and naftifine, and the benzylamine butenafine.
However, onychomycosis has proven to be resistant to most treatments. Nail fungal infections reside in an area difficult to access by conventional topical treatment and anti-fungal drugs cannot readily penetrate the nail plate to reach the infection sites under the nail. Therefore, onychomycosis has traditionally been treated by oral administration of anti-fungal drugs; however, clearly this is undesirable due to the potential for side effects of such drugs, in particular those caused by the more potent anti-fungal drugs such as itraconazole and ketoconazole. An alternative method of treatment of onychomycosis is by removal of the nail before treating with a topically active anti-fungal agent; such a method of treatment is equally undesirable. Systemic antimycotic agents require prolonged use and have the potential for significant side effects. Topical agents have usually been of little benefit, primarily because of poor penetration of the anti-fungal agents into and through the nail mass.
Iontophoresis has been known for many years, as a means to deliver drugs and cosmetic active agents into the skin for therapeutic purposes. It is based on mechanisms, which include (a) iontophoresis, in which a charged ion is repelled from an electrode of the same charge, and (b) electroosmosis, based on the convective movement of solvent that occurs through a charged “pore” in response to the preferential passage of counter-ions when an electric field is applied. While widely used in dermal delivery of active agents, iontophoresis has not been utilized hitherto in the treatment of nail infections. Furthermore, the literature is devoid of pragmatic ways to enable a system, which is practically and conveniently usable for long periods of daily treatment.
In the context of the present invention, the term “iontophoresis” will stand for any method of electrical dermal delivery of substances, including electrotransportation, iontophoresis, electroosmosis, electroporation, and/or a combination thereof. The terms “device,” “iontophoretic device,” “iontophoretic patch,” “electrically operated device,” and “electrically operated patch,” as used herein, will interchangeably stand for any method or device, used for electrical delivery of substances, including electrotransportation, iontophoresis, electroosmosis, and electroporation.
It would therefore be advantageous to have a therapeutic system, based on topical application of a formulation that is capable of penetrating the nail barrier and effectively treating nail fungal diseases, thus avoiding oral administration of anti-fungal drugs and the necessity of removing the nail.