Study and development of encapsulated forms of 4, 5′, 8‐Trimethylpsoralen for topical drug delivery

Trimethylpsoralen (TMP) is often used to treat skin diseases (i.e., psoriasis, vitiligo, etc.). This drug permeates moderately the skin barrier. In the present study, we investigated the effect of formulation on the improvement of TMP skin bioavailability. Three formulations were performed. Each form (liposomes, nanospheres, and EtOH solution) contained 0.05% of TMP. For each preparation, the quantity deposited on the skin surface was 250 µg (Q₀). The TMP percutaneous penetration through ex‐vivo human skin was processed by Franz^® cells (n=4) using a human albumin solution (1.4% w/v) as receiver medium. The percentages of the extracted TMP that permeated through the skin and that were retained in the skin over 24 h, were calculated with respect to Q₀. The values obtained were reported, respectively, as follows: EtOH solution (1.33 vs. 0.08%), liposomes (0.93 vs. 0.93%), and PLG‐nanospheres (0.79 vs. 3.01%). So, considering the correlation between the cumulated amounts of TMP permeated through the skin and the TMP stocked in the skin, the nanosphere form showed the higher quantity of TMP accumulated in the skin structures. On the other hand, the maximum value of the flux (ng/cm²/h) in the steady state of TMP incorporated in each formulation was at 6 h for all formulations: 173.5±1.06 (EtOH solution) > 120.4±1.06 (liposomes) > 93.82±0.88 (PLG‐nanospheres). These results indicate that the controlled release of TMP by incorporation in PLG‐nanospheres may increase drug content in the skin, while maintaining a minimal percutaneous absorption. Finally, this work shows that the PLG‐nanospheres could constitute a promising approach for controlling TMP release in order to maintain its topical activity. Drug Dev. Res. 61:86–94, 2004. © 2004 Wiley‐Liss, Inc.