C ompared with that in previous decades, a prolonged phase of marked stagnation in the development of novel neuropsychopharmacological agents has recently been observed. 1 Along with this lack of breakthroughs, there has been increasing awareness of the need to understand the effectiveness and tolerability patterns of well-established and widely prescribed psychotropic agents. In contrast to research regarding the identification of reliable treatment biomarkers, therapeutic drug monitoring (TDM) is neither novel nor impressively innovative. However, TDM remains among the few valuable routine clinical tools in neuropsychopharmacology that essentially account for interindividual variability. This special issue of Therapeutic Drug Monitoring focuses on the unfolding potential of TDM as part of the clinical routine for neuropsychotropic agents. Scherf-Clavel et al 2 guide us through the frequently unseen parts of the TDM process, including various steps from requesting TDM to obtaining and integrating TDM results into clinical decision algorithms. A critical aspect of TDM utility in clinical routine is the turnaround time, that is, the time between requesting TDM and communicating TDM results. Vincent et al 3 show how short turnaround times for clozapine have the potential to transform TDM into a first-line decision-making tool in sudden or unforeseen situations. These situations may be related to the abrupt drug bioavailability changes linked to immunologic reactions 4 or bariatric operations 5 and may ultimately lead to side effects. 6,7 The studies included in this special issue highlight the value of TDM as part of the treatment of particularly vulnerable patient subgroups such as women in pregnancy and lactation, and children. Hagenkötter et al 8 provide a systematic review of the therapeutic reference ranges for attention-deficit hyperactivity disorder medications in children and adolescents to optimize treatment outcomes. Another systematic review investigated clozapine concentration-to-dose ratios as an index of drug clearance in children and adolescents treated with clozapine for mental disorders. 9 Apart from children and adolescents, TDM holds strong potential in the treatment of women during pregnancy and lactation. Goo et al 10 systematically reviewed evidence on lamotrigine dose adjustments during pregnancy in light of pregnancy-related physiologic changes and the resulting pharmacokinetic alterations. A central challenge in the treatment of women during pregnancy and lactation is drug exposure of the newborn. 11 Because TDM can help quantify drug exposure in newborns during lactation, 11 Le Marois et al 12 present a validated routine technique for the quantification of 14 psychotropic drugs in the plasma and breast milk. Alternative target matrices for TDM include hair and urine. 13 Regarding sex effects, Spadi et al 14 provide unique evidence supporting menstrual cycle phase-dependent patterns in the blood levels of several psychotropic agents. In addition to new technologies, novel metabolites of psy...
