Impact of adult atopic dermatitis on topical drug penetration: assessment by cutaneous microdialysis and tape stripping.

Appropriate methodologies for the determination of drug penetration in diseased skin have not yet been established. The aim of this study was to determine the cutaneous penetration of a metronidazole cream formulation in atopic dermatitis, employing dermal microdialysis and tape strip sampling techniques. Non-invasive measuring methods were used for the quantification of the severity of the dermatitis. Skin thickness and the depth of the microdialysis probes in the skin were measured by 20 MHz ultrasound scanning. Metronidazole concentration, sampled by microdialysis, was 2.4-fold higher in the atopic dermatitis compared with uninvolved skin (p<0.001). Tape stripping methodology did not disclose this difference in penetration. Thus, the skin layer of interest and the integrity of the skin barrier should be considered when selecting sampling methodology. Microdialysis sampling is the method of choice whenever the dermis is the target tissue for topical treatment and a skin disease affecting the barrier function is present.