Cross-reactivity assessment of carbamazepine-10,11-epoxide, oxcarbazepine, and 10-hydroxy-carbazepine in two automated carbamazepine immunoassays: PETINIA and EMIT 2000

Simultaneous determination of 24 antiepileptic drugs and their active metabolites in human plasma by UHPLC-MS/MS

Antiepileptic drugs (AEDs) have narrow therapeutic ranges with large individual variability. Routine therapeutic drug monitoring of AEDs was useful for dose optimization, but the common immunoassays could not meet the detection requirements of AEDs, especially for new generation AEDs. The aim of this study was to validate an ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method for simultaneously quantification of 24 AEDs and their active metabolites in human plasma and comparison with a chemiluminescent immunoassay (Simens ADVIA Centaur). The method validation was performed according to FDA and EMEA guidelines. A one-step protein precipitation by acetonitrile followed a five-fold dilution was performed for sample pretreatment. A 5.2 min gradient separation by methanol and 10 mM ammonium acetate was used for separation at 0.6 mL/min under 45 °C. Both positive and negative electrospray ionization were used. Isotopic internal standard was used for all analytes. The inter-day (36 days) accuracy and precision of quality control samples were - 1.07-13.69% and < 6.70% for all analytes. The stability was acceptable for all analytes under routine storing conditions. A total of 436 valproic acid, 118 carbamazepine, and 65 phenobarbital samples were determined twice by each of the UHPLC-MS/MS and immunoassay. Evaluated by Bland-Altman plot, the mean overestimation of the immunoassay compared to UHPLC-MS/MS was 16.5% for valproic acid, 5.6% for carbamazepine, and 40.3% for phenobarbital.

Development of a microdevice for facile analysis of theophylline in whole blood by a cloned enzyme donor immunoassay

We have developed a microdevice for therapeutic drug monitoring. In this device, dispensing of sample and reagent was accomplished by simple manual operation of a syringe. Moreover, for a simple and rapid measurement, we used cloned enzyme donor immunoassay as a detection principle. These features and the reagent that is enclosed in microdevice beforehand make it possible to complete the facile analysis. In this paper, our model analyte was 1,3-dimethylxanthine (theophylline), a kind of bronchodilator. The fluorescence measurement of theophylline in whole blood was achieved with the limit of detection of 0.73 μg mL-1. This microdevice provides rapid analysis (4 min), requires only a small volume of sample (2 μL) and features simple operation; hence, it is readily applicable to point of care testing.

Effects of major transporter and metabolizing enzyme gene polymorphisms on carbamazepine metabolism in Chinese patients with epilepsy

AIM

The present study aimed to evaluate the effects of SNPs of major transporter and metabolizing enzyme genes on carbamazepine (CBZ) metabolism in Chinese patients with epilepsy.

MATERIALS & METHODS

For 210 epileptic patients treated with CBZ as monotherapy, nine SNPs in candidate genes ABCB1, CYP3A4, CYP3A5, POR and EPHX1 were analyzed by PCR-RFLP or direct sequencing. Serum concentrations of CBZ, carbamazepine-10,11-epoxide (CBZE) and carbamazepine-10,11-trans dihydrodiol (CBZD) were determined by HPLC. Dose-adjusted concentrations of CBZ (CDRCBZ), CBZE (CDRCBZE), CBZD (CDRCBZ D) and CBZD:CBZE ratio were used as evaluation parameters for CBZ metabolism.

RESULTS

The ABCB1 c.3435C>T was significantly associated with the CDR of CBZ and its major metabolites. CYP3A4*1G and CYP3A5*3 could influence CBZ metabolism, while POR*28 had no effect on it. The EPHX1 c.416A>G and c.128G>C variants were significantly associated with CBZD:CBZE ratio.

CONCLUSION

Our data suggest that certain polymorphisms of major transporter and metabolizing enzyme genes could in part influence interindividual variability of CBZ metabolism in Chinese patients with epilepsy.

Impact of interferences including metabolite crossreactivity on therapeutic drug monitoring results

Therapeutic drug monitoring is an integral part of services offered by toxicology laboratories because certain drugs require routine monitoring for dosage adjustment to achieve optimal therapeutic response and avoid adverse drug reactions. Immunoassays are widely used for therapeutic drug monitoring. However, immunoassays suffer from interferences from both exogenous and endogenous compounds including metabolites of the parent drug. Digoxin immunoassays are affected more commonly than any other immunoassays used for therapeutic drug monitoring. Digoxin immunoassays are affected by endogenous digoxin-like immunoreactive substances and exogenous compounds such as various drugs, certain herbal supplements, and Digibind. Carbamazepine is metabolized to carbamazepine 10, 11-epoxide, and the crossreactivity of this metabolite with carbamazepine immunoassay may vary from 0% to 94%. Immunoassays used for measuring concentrations of tricyclic antidepressants are affected by tricyclic antidepressant metabolites and by a number of other drugs. Immunoassays for immunosuppressants are also subjected to significant interferences from metabolites, and liquid chromatography combined with mass spectrometry or tandem mass spectrometry is recommended for therapeutic drug monitoring of immunosuppressants. However, liquid chromatography combined with mass spectrometry may also suffer from interferences, for example, due to ion suppression or from isobaric ions.

Discordant carbamazepine values between two immunoassays: carbamazepine values determined by ADVIA Centaur correlate better with those determined by LC-MS/MS than PETINIA assay

Discordant carbamazepine values as determined by two different immunoassays may be due to different cross-reactivities with the active metabolite carbamazepine 10, 11-epoxide and may cause confusion in interpreting carbamazepine serum levels. In this study, we compared carbamazepine values in samples containing carbamazepine and the epoxide metabolite, as determined by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) and by two commercial carbamazepine immunoassays: the PETINIA and the ADVIA Centaur carbamazepine. Clinical specimens were used for the comparative studies wherein we determined carbamazepine concentrations using the PETINIA, ADVIA Centaur, and LC-MS/MS assays. We observed an excellent correlation between carbamazepine concentrations determined by the ADVIA Centaur and LC-MS/MS methods while carbamazepine values were overestimated using the PETINIA assay. When aliquots of drug-free serum were supplemented with clinically relevant concentrations of the carbamazepine epoxide metabolite, we observed negligible cross-reactivity of epoxide with the ADVIA Centaur assay but over 90% cross-reactivity with the PETINIA assay. We conclude that the ADVIA centaur assay accurately measures carbamazepine concentrations in plasma or serum and that the PETINIA assay significantly overestimates true carbamazepine concentration. Such discordance may cause confusion in interpreting serum carbamazepine levels.

Cetirizine as pH-dependent cross-reactant in a carbamazepine-specific immunoassay

High performance liquid chromatography (HPLC) was hyphenated with a previously reported carbamazepine-specific enzyme-linked immunosorbent assay (ELISA) as a screening approach to water analysis in order to identify possible interferences from transformation products. Treated wastewater was analysed and three substances were recognized by the antibody besides carbamazepine: the metabolites 10,11-dihydro-10,11-epoxycarbamazepine and 2-hydroxycarbamazepine plus the structurally not obviously related antihistamine cetirizine. The molar cross-reactivity against cetirizine was found to be pH-dependent and assessed to be 400% at pH 4.5 and 22% at pH 10.5. Performing the ELISA at pH 10.5 greatly improved the accuracy when carbamazepine was determined in surface and wastewater samples.

Estimation of carbamazepine and carbamazepine-10,11-epoxide concentrations in plasma using mathematical equations generated with two carbamazepine immunoassays

Carbamazepine is metabolized to an active metabolite known as carbamazepine-10,11-epoxide, or simply the "epoxide" metabolite. The presence of this metabolite can have clinically significant implications in therapeutic drug monitoring of carbamazepine, but accurate quantification of the epoxide metabolite is currently limited to chromatographic techniques. In this study, mathematical equations are proposed for the estimation of carbamazepine and epoxide metabolite concentrations based on values generated by common carbamazepine immunoassays. Three immunoassays were studied: particle-enhanced turbidimetric inhibition immunoassay (PETINIA, Siemens Healthcare Diagnostics, Deerfield, IL), ADVIA Centaur (Siemens Healthcare Diagnostics), and a cloned enzyme donor immunoassay (CEDIA; Roche, Indianapolis, IN). Equations were based on observed cross-reactivity of epoxide with the PETINIA (average, 96.2%; range, 86.6%-105.7%) and epoxide cross-reactivity with the ADVIA Centaur assay (average, 6.5%; range, 5.3%-7.7%). In addition, equations were developed using average cross-reactivity of epoxide with the PETINIA and with the CEDIA. Values determined by calculation correlated well with carbamazepine and epoxide concentrations in supplemented and patient samples, for which values of carbamazepine (2.2-12.0 microg/mL [9-51 micromol/L]) and the epoxide metabolite (0.6-2.4 microg/mL) were also verified by liquid chromatography-tandem mass spectrometry.

Monitoring carbamazepine in surface and wastewaters by an immunoassay based on a monoclonal antibody

The pharmaceutical compound carbamazepine (CBZ) is an emerging pollutant in the aquatic environment and may potentially be used as a wastewater marker. In this work, an enzyme-linked immunosorbent assay (ELISA) for the detection of carbamazepine in surface and sewage waters has been developed. The heterogeneous immunoassay is based on a commercially available monoclonal antibody and a novel enzyme conjugate (tracer) that links the hapten via a hydrophilic peptide (triglycine) spacer to horseradish peroxidase. The assay achieves a limit of detection of 24 ng/L and a quantitation range of 0.05-50 microg/L. The analytical performance and figure of merits were compared to liquid chromatography-tandem mass spectrometry after solid-phase extraction. For nine Berlin surface water samples and one wastewater sample, a close correlation of results was observed. A constant overestimation relative to the CBZ concentration of approximately 30% by ELISA is probably caused by the presence of 10,11-epoxy-CBZ and 2-hydroxy-CBZ in the samples. The ELISA displayed cross-reactivities for these compounds of 83% and 14%, respectively. In a first screening of 27 surface water samples, CBZ was detected in every sample with concentrations between 0.05 and 3.2 microg/L. Since no sample cleanup is required, the assay allowed for the determination of carbamazepine with high sensitivity at low costs and with much higher throughput than with conventional methods.

Turbidimetric carbamazepine immunoassay on the ADVIA 1650 and 2400 analyzers is free from interference of antihistamine drugs hydroxyzine and cetirizine

A recent report indicates that hydroxyzine and its active metabolite cetirizine interfere with the particle-enhanced turbidimetric inhibition immunoassay (PENTINA) carbamazepine assay. We studied potential interference of hydroxyzine and cetirizine with the turbidimetric carbamazepine immunoassay on ADVIA 1650 and ADVIA 2400 (Bayer Diagnostics, Tarrytown, NY) analyzers. Aliquots of drug-free serum pools were supplemented with various concentrations of hydroxyzine and cetirizine representing therapeutic, moderate toxic, as well as very toxic concentrations. These samples were assayed by the turbidimetric carbamazepine immunoassay on two analyzers. To study the interference in presence of the analyte, aliquots of a serum pool prepared from patients receiving carbamazepine were further supplemented with various amounts of hydroxyzine and or cetirizine and apparent carbamazepine concentrations were measured again in order to compare with the value of original pool. No apparent carbamazepine concentration was observed when aliquots of drug-free serum were supplemented with hydroxyzine or cetirizine. Moreover, in the carbamazepine pool, the original carbamazepine concentration compared well when aliquots of this serum pool were further supplemented with hydroxyzine or cetirizine. We conclude that the turbidimetric carbamazepine immunoassay is free from interference of hydroxyzine and cetirizine.

Hydroxyzine and Metabolites as a Source of Interference in Carbamazepine Particle-Enhanced Turbidimetric Inhibition Immunoassay (PETINIA)

A 32-year-old epileptic patient with a lengthy history of multiple-drug abuse and psychotic disorders was found to have an elevated serum carbamazepine concentration of 40.5 mg/L (therapeutic range 4-12 mg/L) using particle-enhanced turbidimetric inhibition immunoassay (PETINIA). Serum reanalysis by LC-DAD revealed only high hydroxyzine (HDZ) concentration (HDZ = 0.55 mg/L; therapeutic range <0.1 mg/L), suggesting cross-reactivity between HDZ and PETINIA. To confirm this hypothesis, the authors tested 2 commercially available carbamazepine immunoassays, PETINIA and EMIT 2000, for in vitro cross-reactivity with HDZ and 2 HDZ metabolites (cetirizine and norchlorcyclizine). To determine the frequency of this interaction in a clinical setting, 40 sera of 39 patients taking HDZ without carbamazepine were tested by both immunoassays. For some samples, LC-ESI-MS analysis of HDZ metabolites was performed. Additionally, cross-reactivities produced by other benzhydrylpiperazine drugs were evaluated. in vitro, 5 mg of HDZ, cetirizine, and norchlorcyclizine cross-reacted with PETINIA at 85%, 125%, and 66%, respectively. Conversely, EMIT 2000 showed no cross-reactivity. For PETINIA, erroneous carbamazepine concentrations were detected in 35 out of 40 sera of patients taking HDZ. The magnitude of interference correlated moderately with serum HDZ concentrations (Spearman rho coefficient 0.58, P < 0.001), suggesting a major role for the multiple HDZ metabolites (4 serum metabolites were detected by LC-ESI-MS). Furthermore, other benzhydrylpiperazine drugs (eg, oxatomide) showed in vitro cross-reactivity with PETINIA. In conclusion, HDZ and its metabolites cross-react with carbamazepine PETINIA immunoassay, which could significantly affect the correct interpretation of serum carbamazepine concentrations in patients treated with HDZ.

Carbamazepine is an inhibitor of histone deacetylases

Carbamazepine (CBZ) is a common antiepileptic drug (AED) that acts through multiple mechanisms including blockade and potentiation of cation channels and modulation of neurotransmitter levels. Whether it affects any component of the gene transcription machinery is unknown. Histone deacetylases (HDAC) are important in the regulation of gene expression and are currently considered a potential target for drug development. Using a high-throughput screening assay based on acetylation-dependent gene expression, we identified CBZ as a candidate and proceeded to characterize its effects on HDAC. CBZ induced acetylation of histone H4 in the HepG2 liver carcinoma cell line. CBZ inhibited HDAC 3 and HDAC 7, which are representatives of HDAC class I and II respectively. Quantitative testing in an in vitro assay demonstrated HDAC inhibition with an IC50 of 2 microM. The major active metabolite of CBZ, CBZ-10,11-epoxide, was found to have the same HDAC inhibitory activity. The IC50 is considerably lower than therapeutic plasma levels that are typically achieved in patients (25-51 microM). CBZ shares important clinical characteristics (teratogenicity, activity as a mood stabilizer) with valproic acid, another AED that was recently identified as an inhibitor of HDAC. These observations raise the possibility that HDAC inhibition may contribute to the pharmacological profile of CBZ.

Analytic Performance Evaluation of a New Turbidimetric Immunoassay for Carbamazepine on the ADVIA 1650 Analyzer

Carbamazepine, an anticonvulsant, requires therapeutic drug monitoring. Recently Bayer HealthCare, Diagnostics Division released a turbidimetric immunoassay of carbamazepine on the ADVIA 1650 analyzer. We evaluated the analytic performance of this assay by comparing values obtained with this new assay in sera of 54 patients receiving carbamazepine with the values obtained by using a widely used fluorescence polarization immunoassay (FPIA) and a chemiluminescent immunoassay (CLIA). The new turbidimetric immunoassay for carbamazepine showed excellent precision. The low control showed a total CV of 4.9% (mean 2.86, SD 0.14 microg/mL), the medium control demonstrated a total CV of 3.5% (mean 7.79, SD 0.27 microg/mL), and the high control showed a total CV of 4.8% (mean 16.15, SD 0.78 microg/mL). The assay was linear up to a carbamazepine concentration of 20 microg/mL. The assay showed excellent dilution recovery and recovery of samples supplemented with carbamazepine (mean recovery 102.2%). We observed an excellent correlation between the values obtained by the FPIA (x-axis) assay and the new turbidimetric (y-axis) assay (y = 0.96 x - 0.46, r = 0.99, n = 54). We also observed excellent correlation between the values obtained by the CLIA (x-axis) and the turbidimetric (y-axis) assay (y = 1.10 x -0.32, r = 0.99, n = 54). However, the slope of 1.10 was higher than the slope of 0.96 observed with the regression equation obtained by using values obtained by the FPIA and the turbidimetric assay. The positive bias obtained with the new turbidimetric assay compared with the CLIA assay resulted from lower cross reactivity of carbamazepine 10,11-epoxide, the active metabolite of carbamazepine, with CLIA. On the other hand, the cross reactivity of the metabolite is similar between the new turbidimetric assay and the FPIA assay. We conclude that the new turbidimetric assay can be used for routine monitoring of carbamazepine in clinical laboratories.