Nowadays, the concept of personalized therapy gains momentum. Pharmacogenomics, which represents a first answer to these needs, has the drawback of neglecting some variations of therapy response due to non-genetic factors. The aim of this paper is to investigate the feasibility of a non-genetic approach to personalized therapy, via the point-of-care drug monitoring in biological fluids with electrochemical biosensors. The proposed biosensor is based on the use of P450 enzymes as probe molecules, thanks to their key role in human metabolism. Multiwalled carbon nanotubes are used to enhance biosensor sensitivity. Results show how the proposed system is capable to detect drug amounts within the corresponding pharmacological ranges in human serum.