Behind the Curtain: Therapeutic Drug Monitoring of Psychotropic Drugs from a Laboratory Analytical Perspective

Novel Identification of Cysteinyl Derivatives of Toxic Clozapine Nitrenium Ions and the Effect of Valproic Acid on Metabolite Formation: A Study Using Reprocessed High-Resolution Mass Spectra of Analyzed Therapeutic Drug Monitoring Samples

BACKGROUND

Clozapine (CLZ) use is hampered by the risk of granulocyte toxicity, which is associated with the formation of nitrenium ions and the concurrent use of valproic acid (VPA). These highly reactive nitrenium ions cannot be measured in vivo. Instead, deactivated cysteinyl conjugates may potentially be detected. The aim of this study was to develop a novel method for identifying cysteinylated derivates of CLZ nitrenium ions to investigate the effect of VPA on their formation using therapeutic drug monitoring data.

METHODS

A population comprising 93 VPA comedicated and 162 control patients from a therapeutic drug monitoring (TDM) service in Oslo, Norway, was included. Reprocessing of ultraperformance liquid chromatography high-resolution mass spectra (UHPLC-HR-MS) of previously analyzed TDM samples, combined with the assessment of MS/MS fragmentation patterns, was performed to identify the CLZ cysteinyl conjugates. Smoking, which induces CLZ metabolism, was assessed by detecting cotinine in the reprocessed mass spectra.

RESULTS

By reprocessing the UHPLC-HR-MS files of the TDM analyses and reviewing the MS/MS fragment profiles, four cysteinyl conjugates of CLZ were identified. The formations of CLZ cysteinyl (CLZ-Cys 1+ ) and CLZ- N -oxide cysteinyl (CLZ-NOX-Cys 1+ ) were 1.5-fold ( P = 0.038) and 2.1-fold ( P < 0.001) higher in VPA-treated patients than those in the controls. In agreement with previous studies, a 45% reduction in N -desmethylclozapine formation was observed in VPA-treated patients ( P < 0.001).

CONCLUSIONS

A novel method for detecting cysteinyl conjugates of CLZ was developed. Application of this method indicated that VPA significantly increased the formation of CLZ-Cys 1+ metabolites, which might explain the granulocyte toxicity reported after adding VPA to CLZ treatment. The developed method opens new avenues for investigating CLZ toxicity, e.g. by correlating cysteinyl conjugates and granulocyte counts in patients.

Assessing Pharmacokinetic Correlates of Escitalopram-Related Adverse Drug Reactions

BACKGROUND

To assess the pharmacokinetic correlates of reported adverse drug reactions (ADRs) under antidepressant treatment with escitalopram (ESC) using a large therapeutic drug monitoring database.

METHODS

A large naturalistic sample of inpatients and outpatients prescribed ESC was analyzed. ADRs were classified using the Udvalg for Kliniske Undersogelser side effect rating scale. We compared ESC-treated patients with (n = 35) and without ADRs (n = 273) using ESC plasma concentrations as the primary outcome. We also compared ADR rates in the 2 groups based on 2 cut-off ESC levels reflecting the recommended upper thresholds of the therapeutic reference range of 80 ng/mL, suggested by the consensus therapeutic drug monitoring guidelines, and 40 ng/mL, based on recent meta-analysis data. The effects of age, sex, smoking, daily ESC dose, plasma concentrations, and concentrations corrected for daily dose were included in a binary logistic regression model to predict ADRs.

RESULTS

No differences in clinical, demographic, or pharmacokinetic parameters were observed between patients with and without ADRs ( P > 0.05). Patients with ESC-related ADRs were more frequently diagnosed with psychotic disorders than those without (25% vs. 7.1%, P = 0.004). None of the variables was associated with ADR risk. Overall, ADR rates were not significantly different in patients above versus below thresholds of ESC concentrations (ESC concentrations >40 [n = 59] vs. ≤40 ng/mL [n = 249] and >80 [n = 8] vs. ≤80 ng/mL [n = 300]; P = 0.56 and P = 1.0, respectively).

CONCLUSIONS

No distinct pharmacokinetic patterns underlying ESC-associated ADRs were observed. Further studies with more specific assessments of ADRs in larger cohorts are required to better identify potential underlying patterns.

Changes in Psychotropic Drug Blood Levels After SARS-CoV-2 Vaccination: A Two-Center Cohort Study

BACKGROUND

Limited evidence from case reports suggests that coronavirus disease 2019 (COVID-19) vaccination may interact with the treatment outcomes of psychiatric medications. Apart from clozapine, reports on the effect of COVID-19 vaccination on other psychotropic agents are scarce. This study aimed to investigate the impact of COVID-19 vaccination on the plasma levels of different psychotropic drugs using therapeutic drug monitoring.

METHODS

Plasma levels of psychotropic agents, including agomelatine, amisulpride, amitriptyline, escitalopram, fluoxetine, lamotrigine, mirtazapine, olanzapine, quetiapine, sertraline, trazodone, and venlafaxine, from inpatients with a broad spectrum of psychiatric diseases receiving COVID-19 vaccinations were collected at 2 medical centers between 08/2021 and 02/2022 under steady-state conditions before and after vaccination. Postvaccination changes were estimated as a percentage of baseline.

RESULTS

Data from 16 patients who received COVID-19 vaccination were included. The largest changes in plasma levels were reported for quetiapine (+101.2%) and trazodone (-38.5%) in 1 and 3 patients, respectively, 1 day postvaccination compared with baseline levels. One week postvaccination, the plasma levels of fluoxetine (active moiety) and escitalopram increased by 31% and 24.9%, respectively.

CONCLUSIONS

This study provides the first evidence of major changes in the plasma levels of escitalopram, fluoxetine, trazodone, and quetiapine after COVID-19 vaccination. When planning COVID-19 vaccination for patients treated with these medications, clinicians should monitor rapid changes in bioavailability and consider short-term dose adjustments to ensure safety.