In vitro evaluation of percutaneous absorption of an acyclovir product using intact and tape-stripped human skin.

[PURPOSE] To evaluate the use of a flow-through diffusion cell system to assess the absorption and penetration characteristics of drug (acyclovir) products.

[METHODS] In vitro studies were performed to assess the absorption/penetration of acyclovir using a flow-through diffusion cell system with human skin sections obtained from 19 healthy women following mammoplasty. The skin sections, 200-400 microm thick, were prepared using a dermatome. Acyclovir ointment (approximately 10 mg) spiked with (3)H-labelled acyclovir was applied onto the stratum corneum/epidermis side. The skin sections were continually perfused on the dermis side with sterilized culture medium, Buffered Hanks' Balanced Salt Solution, saturated with a CO(2)/O(2) (5/95%).

[RESULTS] After 24 hours, the percentages of acyclovir-derived radioactivity (based on dose applied) in different components were as follows: stratum corneum (SC), 0.20+0.28; viable skin (VS), 0.40+0.38; effluent fluid (EF), 0.25+0.53. A second set of experiments was performed using tape stripped (10X) skin sections. Levels of acyclovir-derived radioactivity were VS, 1.21+1.43 and EF, 2.65+2.61, which were threefold higher (p < 0.05) for VS and elevenfold higher (p < 0.05) for EF compared to the results obtained with the intact skin sections.

[CONCLUSIONS] The SC is the main barrier layer for the penetration of acyclovir through human skin. The use of the flow-through diffusion cell system provides an appropriate in vitro model to assess the absorption/penetration of acyclovir through human skin layers and therefore can potentially be used for dermal formulation characterization and development.