Skin Permeability of Different Terbinafine Hydrochloride Formulations

The objectives of the study are to determine the in vitro permeability of different terbinafine hydrochloride formulations through human skin and to measure the respective concentrations of each formulation within the exposed skin tissue. The permeation of three commercially available 1% terbinafine hydrochloride formulations and two terbinafine hydrochloride solutions of 10 and 20 mg/ml through human skin was investigated using an in vitro continuous flow-through perfusion system. The terbinafine hydrochloride retained in the skin was extracted and analysed. The terbinafine hydrochloride from the different formulations readily diffused into the skin tissue. However, no flux values for any of the terbinafine hydrochloride formulations through the skin into the receptor fluid were found. The mean terbinafine hydrochloride concentrations in the skin after 24 h exposure to the three commercial formulations were 3.589, 1.590 and 4.219 μg/ml respectively. The mean terbinafine hydrochloride concentrations in the skin after 24 h of exposure to the terbinafine hydrochloride solutions (PBS/Methanol 1:1) of 10 and 20 mg/ml were 85.280 and 154.680 μg/ml respectively. The mean terbinafine hydrochloride concentration in the skin exposed to the 10 mg/ml PBS/Methanol solution was higher than those from the three commercial formulations. Terbinafine seems to accumulate in skin/bind to the skin, rather than to diffuse through the skin into the receptor compartment. This unique pharmacokinetic property of terbinafine hydrochloride may enhance its efficacy as topical antifungal and reduce systemic side effects