A novel approach to quantitative LC-MS/MS: therapeutic drug monitoring of clozapine and norclozapine using isotopic internal calibration

Therapeutic monitoring of plasma clozapine and N-desmethylclozapine (norclozapine): practical considerations

Clozapine dose assessment in treatment-refractory schizophrenia is complicated. There is a narrow margin between an effective and a potentially toxic dose and wide inter-individual variation in clozapine metabolic capacity. Moreover, factors such as changes in smoking habit, infection/inflammation, co-prescription of certain drugs, notably fluvoxamine, and age alter the dose requirement within individuals. Therapeutic drug monitoring (TDM) of plasma clozapine and N-desmethylclozapine (norclozapine) can help assess adherence, guide dosage and guard against toxicity. This article gives an overview of clozapine pharmacokinetics and factors affecting clozapine dose requirements. It then outlines the procedures and processes of clozapine TDM, from taking the blood sample for laboratory assay or point-of-contact (finger-prick) testing (POCT) to interpreting and acting on the results.

Calibration Practices in Clinical Mass Spectrometry: Review and Recommendations

Background

Calibration is a critical component for the reliability, accuracy, and precision of mass spectrometry measurements. Optimal practice in the construction, evaluation, and implementation of a new calibration curve is often underappreciated. This systematic review examined how calibration practices are applied to liquid chromatography-tandem mass spectrometry measurement procedures.

Methods

The electronic database PubMed was searched from the date of database inception to April 1, 2022. The search terms used were "calibration," "mass spectrometry," and "regression." Twenty-one articles were identified and included in this review, following evaluation of the titles, abstracts, full text, and reference lists of the search results.

Results

The use of matrix-matched calibrators and stable isotope-labeled internal standards helps to mitigate the impact of matrix effects. A higher number of calibration standards or replicate measurements improves the mapping of the detector response and hence the accuracy and precision of the regression model. Constructing a calibration curve with each analytical batch recharacterizes the instrument detector but does not reduce the actual variability. The analytical response and measurand concentrations should be considered when constructing a calibration curve, along with subsequent use of quality controls to confirm assay performance. It is important to assess the linearity of the calibration curve by using actual experimental data and appropriate statistics. The heteroscedasticity of the calibration data should be investigated, and appropriate weighting should be applied during regression modeling.

Conclusions

This review provides an outline and guidance for optimal calibration practices in clinical mass spectrometry laboratories.

Calibrating from Within: Multipoint Internal Calibration of a Quantitative Mass Spectrometric Assay of Serum Methotrexate

BACKGROUND

Clinical LC-MS/MS assays traditionally require that samples be run in batches with calibration curves in each batch. This approach is inefficient and presents a barrier to random access analysis. We developed an alternative approach called multipoint internal calibration (MPIC) that eliminated the need for batch-mode analysis.

METHODS

The new approach used 4 variants of 13C-labeled methotrexate (0.026-10.3 µM) as an internal calibration curve within each sample. One site carried out a comprehensive validation, which included an evaluation of interferences and matrix effects, lower limit of quantification (LLOQ), and 20-day precision. Three sites evaluated assay precision and linearity. MPIC was also compared with traditional LC-MS/MS and an immunoassay.

RESULTS

Recovery of spiked analyte was 93%-102%. The LLOQ was validated to be 0.017 µM. Total variability, determined in a 20-day experiment, was 11.5%CV. In a 5-day variability study performed at each site, total imprecision was 3.4 to 16.8%CV. Linearity was validated throughout the calibrator range (r2 > 0.995, slopes = 0.996-1.01). In comparing 40 samples run in each laboratory, the median interlaboratory imprecision was 6.55%CV. MPIC quantification was comparable to both traditional LC-MS/MS and immunoassay (r2 = 0.96-0.98, slopes = 1.04-1.06). Bland-Altman analysis of all comparisons showed biases rarely exceeding 20% when MTX concentrations were >0.4 µM.

CONCLUSION

The MPIC method for serum methotrexate quantification was validated in a multisite proof-of-concept study and represents a big step toward random-access LC-MS/MS analysis, which could change the paradigm of mass spectrometry in the clinical laboratory.

Effect of fluvoxamine augmentation and smoking on clozapine serum concentrations

BACKGROUND

Clozapine (CLZ) is metabolized via cytochrome P450 CYP1A2 to N-desmethylclozapine (NCLZ). Smoking induces CYP1A2 thereby increasing clozapine metabolism whereas fluvoxamine inhibits CYP1A2. Studies suggest that the beneficial effect of fluvoxamine augmentation in raising serum clozapine concentrations also occurs when serum concentrations are low due to smoking. Yet, little is known about the influence of fluvoxamine augmentation on clozapine serum concentrations in smoking versus non-smoking patients.

METHODS

A TDM database was analyzed. Serum concentrations of CLZ, NCLZ, dose-adjusted serum concentrations (C/D) and metabolite-to-parent ratios (MPR) were compared using non-parametrical tests in four groups: clozapine-monotherapy in non-smokers (V_NS, n = 28) and smokers (V_S, n = 43); combined treatment with clozapine and fluvoxamine in non-smokers (V_NS+F, n = 11) and smokers (V_S+F, n = 43).

RESULTS

The CLZ monotherapy smoking group showed lower values of C/D CLZ of -38.6% (p < 0.001), C/D NCLZ -35.6% (p < 0.001) and a higher MPR (p = 0.021) than in the non-smoking group. The combination of CLZ and fluvoxamine in non-smoking patients led to higher C/D values: C/D CLZ +117.9% (p < 0.001), C/D NCLZ +60.8% (p = 0.029) while the MPR did not differ between groups (p = 0.089). Changes were comparable to fluvoxamine augmentation in the smoking group with increased C/D CLZ of +120.1% (p < 0.001), C/D NCLZ of +85.8% (p < 0.001) and lower MPR (p = 0.006).

CONCLUSIONS

Smoking in clozapine monotherapy reduced median dose-adjusted serum concentrations more than a third. Combined treatment with fluvoxamine and clozapine led to higher median C/D values in both, smokers and non-smokers. The opposing effects of CYP1A2 induction by smoking and inhibition by fluvoxamine on clozapine serum concentrations balanced out.

A Chitosan-Carbon Nanotube-Modified Microelectrode for In Situ Detection of Blood Levels of the Antipsychotic Clozapine in a Finger-Pricked Sample Volume

The antipsychotic clozapine is the most effective medication available for schizophrenia and it is the only antipsychotic with a known efficacious clinical range. However, it is dramatically underutilized due to the inability to test clozapine blood levels in finger-pricked patients' samples. This prevents obtaining immediate blood levels information, resulting in suboptimal treatment. The development of an electrochemical microsensor is presented, which enables, for the first time, clozapine detection in microliters volume whole blood. The sensor is based on a microelectrode modified with micrometer-thick biopolymer chitosan encapsulating carbon nanotubes. The developed sensor detects clozapine oxidation current, in the presence of other electroactive species in the blood, which generate overlapping electrochemical signals. Clozapine detection, characterized in whole blood from healthy volunteers, displays a sensitivity of 32 ± 3.0 µA cm^-2 µmol^-1 L and a limit-of-detection of 0.5 ± 0.03 µmol L^-1 . Finally, the developed sensor displays a reproducible electrochemical signal (0.6% relative standard deviation) and high storage stability (9.8% relative standard deviation after 8 days) in serum samples and high repeatability (9% relative standard deviation for the 5th repetition) in whole blood samples. By enabling the rapid and minimally invasive clozapine detection at the point-of-care, an optimal schizophrenia treatment is provided.

Development and validation of a gas chromatography/tandem mass spectrometry method for simultaneous quantitation of several antipsychotics in human plasma and oral fluid

RATIONALE

Antipsychotic drugs are prescription medications used to treat psychotic disorders, such as schizophrenia, schizoaffective disorder, or psychotic depression. With several antipsychotic drugs currently available all over the world, this class of drugs has quickly gained importance in both the clinical and forensic context. This work describes the development and validation of a methodology for the determination of seven antipsychotic drugs in plasma and oral fluid samples.

METHODS

The antipsychotic drugs (chlorpromazine, clozapine, haloperidol, olanzapine, quetiapine, cyamemazine and, levomepromazine) were isolated from 0.2 mL of oral fluid and 0.5 mL of plasma using solid-phase extraction (SPE) following analysis by gas chromatography/tandem mass spectrometry (GC/MS/MS). The method was validated according to the international guidelines in terms of selectivity, linearity, accuracy, precision and recovery.

RESULTS

The procedure was linear within 2-600 ng/mL (plasma) and 2-400 ng/mL (oral fluid), the intervals varying according to the compound; a mean R² value of 0.99 was obtained and the calibrator's accuracy (mean relative error) was within a ±15 % interval for all concentrations. The limits of detection ranged from 1 to 10 ng/mL. Within- and between-run precision and accuracy were acceptable for all studied compounds. The extraction efficiency of the process ranged from 79% to 95%. The method was applied to authentic specimens.

CONCLUSIONS

The described method was proven selective and sensitive for the determination of antipsychotics in low sample volumes using SPE and GC/MS/MS. This method was considered suitable not only for routine analysis of patients undergoing antipsychotic treatment (to evaluate compliance), but also in forensic scenarios where the studied compounds may be involved. To the best of our knowledge, this is the first work that reports the determination of antipsychotic drugs in oral fluid using MS/MS.

Women Administered Standard Dose Imatinib for Chronic Myeloid Leukemia Have Higher Dose-Adjusted Plasma Imatinib and Norimatinib Concentrations Than Men

BACKGROUND

The standard dose of imatinib for the treatment of chronic-phase chronic myeloid leukemia (CML) is 400 mg·d. A predose plasma imatinib concentration of >1 mg·L is associated with improved clinical response. This study aimed to assess the plasma imatinib and norimatinib concentrations attained in patients with chronic myeloid leukemia administered standard doses of imatinib adjusted for dose, age, sex, body weight, and response.

METHODS

We evaluated data from a cohort of patients treated between 2008 and 2014 with respect to dose, age, sex, body weight, and response.

RESULTS

The study comprised 438 samples from 93 patients (54 male, 39 female). The median imatinib dose was 400 mg·d in men and in women. The plasma imatinib concentration ranged 0.1-5.0 mg·L and was below 1 mg·L in 20% and 16% of samples from men and women, respectively. The mean dose normalized plasma imatinib and norimatinib concentrations were significantly higher in women in comparison with men. This was partially related to body weight. Mixed effects ordinal logistic regression showed no evidence of an association between sex and plasma imatinib (P = 0.13). However, there was evidence of an association between sex and plasma norimatinib, with higher norimatinib concentrations more likely in women than in men (P = 0.02).

CONCLUSIONS

Imatinib therapeutic drug monitoring only provides information on dosage adequacy and on short-term adherence; longer-term adherence cannot be assessed. However, this analysis revealed that approximately 1 in 5 samples had a plasma imatinib concentration <1 mg·L, which was suggestive of inadequate dosage and/or poor adherence and posed a risk of treatment failure. Higher imatinib exposure in women may be a factor in the increased rate of long-term, stable, deep molecular response (undetectable breakpoint cluster-Abelson (BCR-ABL) transcript levels with a PCR sensitivity of 4.5 log, MR4.5) reported in women.

Fusing Sensor Paradigms to Acquire Chemical Information: An Integrative Role for Smart Biopolymeric Hydrogels

The Information Age transformed our lives but it has had surprisingly little impact on the way chemical information (e.g., from our biological world) is acquired, analyzed and communicated. Sensor systems are poised to change this situation by providing rapid access to chemical information. This access will be enabled by technological advances from various fields: biology enables the synthesis, design and discovery of molecular recognition elements as well as the generation of cell-based signal processors; physics and chemistry are providing nano-components that facilitate the transmission and transduction of signals rich with chemical information; microfabrication is yielding sensors capable of receiving these signals through various modalities; and signal processing analysis enhances the extraction of chemical information. The authors contend that integral to the development of functional sensor systems will be materials that (i) enable the integrative and hierarchical assembly of various sensing components (for chemical recognition and signal transduction) and (ii) facilitate meaningful communication across modalities. It is suggested that stimuli-responsive self-assembling biopolymers can perform such integrative functions, and redox provides modality-spanning communication capabilities. Recent progress toward the development of electrochemical sensors to manage schizophrenia is used to illustrate the opportunities and challenges for enlisting sensors for chemical information processing.

Advances in bioanalytical techniques to measure steroid hormones in serum

Steroid hormones are measured clinically to determine if a patient has a pathological process occurring in the adrenal gland, or other hormone responsive organs. They are very similar in structure making them analytically challenging to measure. Additionally, these hormones have vast concentration differences in human serum adding to the measurement complexity. GC–MS was the gold standard methodology used to measure steroid hormones clinically, followed by radioimmunoassay, but that was replaced by immunoassay due to ease of use. LC–MS/MS has now become a popular alternative owing to simplified sample preparation than for GC–MS and increased specificity and sensitivity over immunoassay. This review will discuss these methodologies and some new developments that could simplify and improve steroid hormone analysis in serum.

Emerging applications of metabolomics in drug discovery and precision medicine

Metabolomics is an emerging 'omics' science involving the comprehensive characterization of metabolites and metabolism in biological systems. Recent advances in metabolomics technologies are leading to a growing number of mainstream biomedical applications. In particular, metabolomics is increasingly being used to diagnose disease, understand disease mechanisms, identify novel drug targets, customize drug treatments and monitor therapeutic outcomes. This Review discusses some of the latest technological advances in metabolomics, focusing on the application of metabolomics towards uncovering the underlying causes of complex diseases (such as atherosclerosis, cancer and diabetes), the growing role of metabolomics in drug discovery and its potential effect on precision medicine.

Liquid chromatography tandem mass spectrometry in the clinical laboratory

Clinical laboratory medicine has seen the introduction and evolution of liquid chromatography tandem mass spectrometry in routine clinical laboratories over the last 10–15 years. There still exists a wide diversity of assays from very esoteric and highly specialist manual assays to more simplified kit-based assays. The technology is not static as manufacturers are continually making improvements. Mass spectrometry is now commonly used in several areas of diagnostics including therapeutic drug monitoring, toxicology, endocrinology, paediatrics and microbiology. Some of the most high throughput analyses or common analytes include vitamin D, immunosuppressant monitoring, androgen measurement and newborn screening. It also offers flexibility for the measurement of analytes in a variety of different matrices which would prove difficult with immunoassays. Unlike immunoassays or high-pressure liquid chromatography assays using ultraviolet or fluorescence detection, mass spectrometry offers better specificity and reduced interferences if attention is paid to potential isobaric compounds. Furthermore, multiplexing, which enables multiple analytes to be measured with the same volume of serum is advantageous, and the requirement for large sample volumes is decreasing as instrument sensitivity increases. There are many emerging applications in the literature. Using mass spectrometry to identify novel isoforms or modified peptides is possible as is quantification of proteins and peptides, with or without protein digests. Future developments by the manufacturers may also include mechanisms to improve the throughput of samples and strategies to decrease the level of skill required by the operators.