Leloux, Megan R.

Background: Clozapine is the preferred medication for treatment-resistant schizophrenia with therapeutic drug monitoring (TDM) suggested to mediate its safe and effective use. However, clozapine TDM is not a ubiquitous element of care in clinical practice. Understanding the current state of clinicians' perceptions of and barriers to clozapine TDM is a crucial step in improving its use. Methods: A survey related to the use, perceptions, and barriers of clozapine TDM was distributed across multiple national organizations in the United States, representing several disciplines. Results: Most of the 190 respondents were consultants or attending physicians (42.5%) or pharmacists (52.3%). Nearly 80% of respondents had ordered clozapine level measurements in the year before completing the survey but identified slow turnaround time (TaT) as an important barrier; 73.5% of respondents noted that level measurements were performed at an offsite laboratory. Although 86.8% agreed that clozapine levels should be checked once an initial target dose was reached, less than half would subsequently order clozapine level measurements routinely, unless clinical factors such as nonadherence (96.5% agreement), new interaction (94.5% agreement), or change in smoking status (94.5% agreement) occurred. More pharmacists than prescribers indicated confidence in interpreting and clinically applying clozapine TDM results (84.6% versus 70.1%, P = 0.024), with a similar finding between the groups regarding faster clozapine TDM TaT, resulting in improved patient safety (89.0% versus 68.7% agreement, P = 0.003). In addition, more pharmacists would also conduct clozapine TDM in the setting of an acute inflammatory or infectious process (84.9% versus 61.2%, P = 0.002). Conclusions: These data provide insights into clozapine TDM perception, availability, TaT, and barriers. Further research is required to assess whether a faster TaT and more frequent clozapine TDM positively influence patient outcomes from a safety and effectiveness perspective.

Abstract Purpose/Background Clozapine requires careful monitoring to minimize adverse reactions and optimize response. Because of variable pharmacokinetics and interpatient variability, guidelines recommend therapeutic drug monitoring (TDM), although practical guidance is limited. This study aims to characterize patient factors associated with TDM, rates of TDM use over time, turnaround times of TDM results, and influence of institutional initiatives aimed to improve TDM. Methods/Procedures A retrospective chart review was conducted at a large 2000-bed academic medical center from August 1, 2015, to November 26, 2023. Adult patients who were administered clozapine during medical or psychiatric inpatient hospitalizations were included. Data collected included patient demographics, clozapine TDM ordering, and clozapine TDM turnaround time. Yearly TDM rates were analyzed to evaluate the impact of various institutional clozapine-related initiatives on TDM practices. Results There were 679 encounters involving 334 patients; 62.7 % were men, and 84.4% were White. Younger patients were less likely to have levels drawn (odds ratio 0.98, confidence interval 0.97–0.99), while self-identified Asian patients more likely (odds ratio 7.54, confidence interval 1.60–35.42). TDM rates increased significantly over time for both medical ( P = 0.002) and psychiatric ( P < 0.001) admission types, with turnaround times improving from 66.07 hours in 2016 to 28.65 hours in 2022. Overall, TDM annual rates increased from 46.2% in 2015 to 69.6% in 2023. The time-period before and after an institutional initiative, which improved TDM turnaround time, was associated with improvements of TDM rates (36.2% vs 67.9%, P < 0.001) Conclusions This study highlights an increase in clozapine TDM use during the study period, but use remained suboptimal. Improvement of turnaround time was associated with increased TDM rates.