Opinion PaperThe Appropriately Designed TDM Clinical Trial: Endpoints, Pitfalls, and Perspectivesvan Gelder, Teun MD, PhD Author Information Department of Clinical Pharmacy and Toxicology, Leiden University Medical Center, Leiden, The Netherlands. Correspondence: Teun van Gelder, Leiden University Medical Center, Albinusdreef 2, 2333 ZA Leiden, The Netherlands (e-mail: [email protected]). In the last 3 years, T. van Gelder has received lecture fees from Chiesi and Astellas, in addition to consulting fees from Roche Diagnostics, Thermo Fisher, Vitaeris, CSL Behring, Astellas, and Aurinia Pharma. In all cases, money has been transferred to hospital accounts, and none has been paid to his personal bank accounts. T. van Gelder does not have employment or stock ownership at any of these companies, and neither does he have patents or patent applications. No funding was provided for this article. Therapeutic Drug Monitoring 45(1):p 6-10, February 2023. | DOI: 10.1097/FTD.0000000000001010 Buy Metrics Abstract Background: Appropriately designed clinical trials can provide the evidence needed to broadly implement therapeutic drug monitoring (TDM). In the past 30 years, some stunning successes but also some fascinating failures in demonstrating the benefits of TDM have been observed. Future TDM studies can be designed based on this experience. Methods: The manuscript is based on a combination of personal experience and published articles and discusses several aspects of the design and conduct of TDM studies. Results: Recommendations are provided to reduce the risk of protocol violations and to maximize the potential impact of a TDM study on clinical practice. Conclusions: There are lessons that can be learned from previous experience, and this article gives an overview of potential TDM study designs, endpoints, pitfalls, and perspectives. Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.