Permeation studies of novel terbinafine formulations containing hydrophobins through human nails in vitro.

Existing treatments of onychomycosis are not satisfactory. Oral therapies have many side effects and topical formulations are not able to penetrate into the human nail plate and deliver therapeutical concentrations of active agent in situ. The purpose of the present study was to determine the amount of terbinafine, which permeates through the human nail plate, from liquid formulations containing enhancers, namely hydrophobins A-C in the concentration of 0.1% (w/v). The used reference solution contained 10% (w/v) of terbinafine in 60% (v/v) ethanol/water without enhancer. Permeability studies have been performed on cadaver nails using Franz diffusion cells modified to mount nail plates and filled with 60% (v/v) ethanol/water in the acceptor chamber. Terbinafine was quantitatively determined by HPLC. The amount of terbinafine remaining in the nail was extracted by 96% ethanol from pulverized nail material after permeation experiment and presented as percentage of the dry nail weight before the milling test. Permeability coefficient (PC) of terbinafine from reference solution was determined to be 1.52E-10 cm/s. Addition of hydrophobins improved PC in the range of 3E-10 to 2E-9 cm/s. Remaining terbinafine reservoir in the nail from reference solution was 0.83% (n=2). An increase of remaining terbinafine reservoir in the nail was observed in two out of three tested formulations containing hydrophobins compared to the reference. In all cases, known minimum inhibitory concentration of terbinafine for dermatophytes (0.003 microg/ml) has been exceeded in the acceptor chamber of the diffusion cells. All tested proteins (hydrophobins) facilitated terbinafine permeation after 10 days of permeation experiment, however one of them achieved an outstanding enhancement factor of 13.05 compared to the reference. Therefore, hydrophobins can be included in the list of potential enhancers for treatment of onychomycosis.

Investigation of different formulations for drug delivery through the nail plate.

Topical therapies for nail diseases are limited by keratinized cells in the human nail plate. An optimal permeation enhancer would not only improve drug delivery through the nail plate, but would also open new possibilities for treating neighboring target sites if systemic circulation is reached. The aim of the present work was to identify permeation enhancers and to improve the understanding of physicochemical parameters that influence drug permeation. Caffeine served as the model drug, and formulations were prepared in water and 20% (v/v) ethanol/water solutions. Tested enhancers were urea, dimethyl sulfoxide (DMSO), methanol, N-acetyl-L-cysteine (NAC), docusate sodium salt (DSS), boric acid, and fungal proteins, such as hydrophobins. Permeability studies employed cadaver nails in modified Franz-type diffusion cells. The permeability coefficient of caffeine in ethanol/water was determined to be 1.56 E-08 cm/s and was improved to 2.27 E-08 cm/s by the addition of NAC. Formulations containing either methanol or DMSO showed the highest permeability coefficients in the range of 5-7.5 E-08 cm/s. Enhancers could be classified according to their permeation enhancement: methanol>class II hydrophobins>DMSO>followed by class I hydrophobins and urea. Ethanol at a concentration of 20% (v/v) in water did not influence swelling of nail samples. Hydrophobins are suggested to be efficient in drug delivery through the nail plate.