Monitoring of plasma drug concentrations is necessary for the efficacy and safety of therapeutic medicines. Nonetheless, repetitive collection of whole blood followed by analysis of plasma samples with standard methods delays representation of crucial results to clinicians and timely control of drug administration to patients. Skin is an easily accessible organ; a portion of systemically circulating drug molecules is diffused to the dermal interstitial fluid through capillaries. Therefore, the compound‘s concentrations in the fluid could likely reflect the plasma pharmacokinetics. To approach such local and narrow dermal space in situ, in this study we constructed a microsensing system for real-time drug detection with a needle-type boron-doped diamond (BDD) electrode, a state-of-the-art electrochemical material that detects chemical compounds by redox reaction. The sensor with a small diameter of 20 µm, is minimally invasive and allows passage into the otherwise inaccessible interface. As a test drug we selected doxorubicin, which is widely used for oncotherapy but can induce cardiotoxicity. In an in vitro experiment with a BDD microsensor, doxorubicin elicited a prominent reductive current in response to applied negative potential. The current was minimally disturbed by addition of glucose, uric acid, ascorbic acid, or fatty acids, each of which is abundantly present in the dermal interstitial fluids. Calibration curve showed a linear relation in the therapeutic window and determined the limit of detection as ~nM. Finally, the BDD microsensor was embedded in the skin and the tip was placed within the dermis layer in anesthetized live hairless rats; after doxorubicin was intravenously administrated, the local pharmacokinetics was continuously tracked for >1 hour with the C_max and T_max 3.06 ± 1.40 nM and 33.57 ± 20.56 mins, respectively (n = 7). By combining a suitable formula that can link the local measurements to plasma data, this advanced microsensing system subjected to the skin may be applicable to the development of a real-time monitoring method for systemic drug concentrations.