Allen, Nicholas D.

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.