Subcutaneous microdialysis in the awake rat.

Background. Microdialysis is a valued method to study the pharmacokinetics of drug distribution from an injection site or to a tumor site. The objective of this study was to assess the feasibility of prolonged use of subcutaneously implanted microdialysis catheters to assess local retention and systemic uptake of carboplatin in rats post anesthetic recovery.

Methods. Twelve rats were used: one control rat and 11 treatment rats. The control rat was used to outline the surgical implantation technique of the microdialysis catheter. Treatment rats were administered 5mg carboplatin in poloxamer 407 and divided in two treatment cohorts. Microdialysis catheters were used in both cohorts to collect extracellular fluid. Placement technique was modified between the two cohorts. Treatment cohort 1 (n=6) had the microdialysis catheter implanted in the wound bed, sutured in place and tunneled subcutaneously along the dorsum to exit dorsally in the cervical area. The ends were secured to a Velcro strip sutured to the dorsal cervical skin to avoid trauma by the rat. Treatment cohort 2 (n=5) had the catheter looped around the right hind limb, with the functional part sutured in place in the wound bed, and tunneled through a subcutaneously implanted sterile intravenous line exiting dorsally in the cervical area. The ends were maintained within the IV line and held in place with wound clips. Results. All 11 microdialysis catheters in the treatment cohorts were functional immediately after implantation, but only one out of 11 microdialysis catheters in the treatment cohorts was functional at 24hrs, and none at 48hrs. Discussion. The results of this study suggest that microdialysis catheters cannot be maintained in unanesthetized rats without further modification of the implantation protocol.