Perceptions, Use, and Barriers of Clozapine Therapeutic Drug Monitoring in the United States: A Multidisciplinary Survey Study

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.