Dermal Microdialysis Sampling in Vivo

Microdialysis sampling of the dermis in vivo was accomplished using a linear microdialysis probe. In contrast to previous studies using a commercial cannula-style microdialysis probe, the linear probe had no effect on the flux of drug through the skin in vitro. The extent of tissue damage in vivo due to probe implantation was evaluated by histological examination and microdialysis delivery studies. Tissue damage due to implantation of the linear probe was minimal with no bleeding or edema observed. Infiltration of lymphocytes into the tissue was observed beginning 6 hours after probe implantation with scar tissue beginning to form after approximately 32 hours. The infiltration of lymphocytes had no effect on the behavior of implanted microdialysis probes. Delivery of 5-fluorouracil was between 20 and 25% for six different probes implanted in six different animals demonstrating good probe-to-probe and implantation-to-implantation reproducibility. Constant delivery was maintained for at least 24 hours in all cases indicating that experiments of at least 24 hour duration are feasible. The dermal concentration of topically applied 5-FU cream, Efudex^®, was continuously monitored by an implanted microdialysis probe demonstrating the feasibility of this technique as for monitoring skin drug levels in vivo. The dermal concentration of 5-FU following topical application was approximately 40-fold higher for in vitro excised skin than for in vivo intact skin.