Local skin pharmacokinetics of talarozole, a new retinoic acid metabolism-blocking agent.

Talarozole is a new highly potent and selective azole derivative which inhibits cytochrome-P450-dependent all-trans-retinoic acid catabolism. It is in clinical development for the treatment of psoriasis and acne. However, no local pharmacokinetic data on the diffusion behaviour of talarozole in the skin itself are available. As topical application might be an interesting alternative to oral therapy because of the reduced systemic side effects, the aim of this study was to assess the transdermal behaviour of topically applied talarozole, including its within-skin distribution. Franz diffusion cell experiments with talarozole dissolved in different pharmaceutically relevant solvents (i.e. propylene glycol, oleolyl macrogol glyceride, isopropyl myristate, diethylene glycol monoethylether, ethanol, caprylic/capric triglyceride and caprylocaproyl macrogol glyceride) were performed to assess the transdermal behaviour of talarozole. Talarozole slightly diffused into the skin only when dissolved in propylene glycol, isopropyl myristate or ethanol. Although only 0.1% of the dose applied was found in the skin itself after 12-24 h, this was sufficient to achieve local concentrations well above the half-maximal inhibitory concentration value for talarozole. The distribution of talarozole within the skin was investigated: 80% was located in the epidermis, while the remaining 20% was found in the dermis. The epidermal concentration of talarozole achieved after a single topical application was sufficiently high to enable the potential induction of local retinoid-like effects.