How suitable are currently used carbamazepine immunoassays for quantifying carbamazepine-10,11-epoxide in serum samples?

An isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS)-based candidate reference measurement procedure for the quantification of carbamazepine in human serum and plasma

OBJECTIVES

An isotope dilution liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS)-based candidate reference measurement procedure (RMP) was developed and validated to accurately measure serum and plasma concentrations of carbamazepine.

METHODS

Quantitative nuclear magnetic resonance (qNMR) spectroscopy was used to determine the absolute content of the reference material, ensuring its traceability to SI units. The separation of carbamazepine from potential interferences, whether known or unknown, was achieved using a C18 column. A protein precipitation protocol followed by a high dilution step was established for sample preparation. Assay validation and determination of measurement uncertainty were performed in accordance with the guidelines of the Clinical and Laboratory Standards Institute, the International Conference on Harmonization (ICH), and the Guide to the Expression of Uncertainty in Measurement (GUM). In order to demonstrate equivalence to the already existing RMP a method comparison study was performed.

RESULTS

The RMP was proven to be highly selective and specific with no evidence of a matrix effect, allowing for quantification of carbamazepine within the range of 0.800-18.0 μg/mL. Intermediate precision and repeatability (n=60 measurements) was found to be <1.6 % and <1.3 % over all concentration levels and independent from the matrix. The relative mean bias ranged from -0.1 to 0.6 % for native serum and from -0.3 to -0.1 % for Li-heparin plasma levels. The measurement uncertainties for single measurements and target value assignment were found to be <1.8 % and <1.3 %, respectively. Method comparison showed a good agreement between the Joint Committee of Traceability in Laboratory Medicine (JCTLM) listed RMP and the candidate RMP resulting in a Passing-Bablok regression equation with a slope of 1.01 and an intercept of -0.01. The bias in the patient cohort was found to be 0.9 %.

CONCLUSIONS

We present a novel LC-MS/MS-based candidate RMP for carbamazepine in human serum and plasma which provides a traceable and reliable platform for the standardization of routine assays and evaluation of clinically relevant samples.

An isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS)-based candidate reference measurement procedure for the quantification of carbamazepine-10,11-epoxide in human serum and plasma

OBJECTIVES

A reference measurement procedure (RMP) using isotope dilution liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS) was developed and validated with the aim of accurately measuring carbamazepine-10,11-epoxide concentrations in human serum and plasma.

METHODS

To establish traceability to SI units, the absolute content of the reference material was determined using quantitative nuclear magnetic resonance (qNMR) spectroscopy. As sample preparation a protein precipitation protocol followed by a high dilution step was established. Chromatographic separation from carbamazepine and potential metabolites was achieved using a C18 stationary phase. Selectivity, specificity, matrix effects, precision and accuracy, inter-laboratory equivalence, and uncertainty of measurement were evaluated based on guidelines from the Clinical and Laboratory Standards Institute, the International Conference on Harmonization, and the Guide to the Expression of Uncertainty in Measurement.

RESULTS

The RMP demonstrated very good selectivity and specificity, showing no evidence of a matrix effect. This enabled accurate quantification of carbamazepine-epoxide in the concentration range of 0.0400-12.0 μg/mL. The intermediate precision was found to be less than 2.1 %, and the repeatability coefficient of variation (CV) ranged from 1.2 to 1.8 % across all concentration levels. Regarding accuracy, the relative mean bias varied from 1.4 to 2.5 % for native serum levels and from 1.4 to 3.5 % for Li-heparin plasma levels. The measurement uncertainty for single measurements ranged from 1.6 to 2.1 %.

CONCLUSIONS

In this study, we introduce a new LC-MS/MS-based candidate RMP for accurately measuring carbamazepine-10,11-epoxide in human serum and plasma. This novel method offers a traceable and dependable platform, making it suitable for standardizing routine assays and assessing clinically relevant samples.

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.

Repurposing Carbamazepine To Treat Gonococcal Infection in Women: Oral Delivery for Control of Epilepsy Generates Therapeutically Effective Levels in Vaginal Secretions

Neisseria gonorrhoeae has developed resistance to all previous antibiotics used for treatment. This highlights a crucial need for novel antimicrobials to treat gonococcal infections. We previously showed that carbamazepine (Cz), one of the most commonly prescribed antiepileptic drugs, can block the interaction between gonococcal pili and the I-domain region of human complement receptor 3 (CR3)-an interaction that is vital for infection of the female cervix. We also show that Cz can completely clear an established N. gonorrhoeae infection of primary human cervical cells. In this study, we quantified Cz in serum, saliva, and vaginal fluid collected from 16 women who were, or were not, regularly taking Cz. We detected Cz in lower reproductive tract mucosal secretions in the test group (women taking Cz) at potentially therapeutic levels using a competitive ELISA. Furthermore, we found that Cz concentrations present in vaginal fluid from women taking this drug were sufficient to result in a greater than 99% reduction (within 24 h) in the number of viable gonococci recovered from ex vivo, human, primary cervical cell infections. These data provide strong support for the further development of Cz as a novel, host-targeted therapy to treat gonococcal cervicitis.

Determination of serum carbamazepine and its metabolite by validated tandem mass spectrometric method and the effect of carbamazepine on various hematological and biochemical parameters

OBJECTIVES

The study aimed to develop a validated LC-MS / MS method for the measurement of carbamazepine and carbamazepine-10,11-epoxide (CBZE) levels, to compare the carbamazepine concentrations measured by AbSciex API 3200 LC-MS/MS and Beckman Coulter Emit® 2000 immunoassay and to investigate the effect of carbamazepine concentrations on various hematological and biochemical parameters.

METHODS

For the measurement of carbamazepine and CBZE levels, a validated LC-MS / MS method was developed. Serum carbamazepine levels of patients were measured by AbSciex API 3200 LC-MS / MS and Beckman Coulter Emit® 2000 immunoassay. Biochemical, hematological parameters, and hormone levels were measured by Beckman-Coulter AU 5800 (Beckman Coulter, Brea, USA), Beckman Coulter LH 780 (Beckman Coulter, Miami, FL, USA), and Cobas 6000 (Roche Diagnostics, Germany) analyzers, respectively.

RESULTS

The imprecision values for all analytes were less than 7.0 %. The correlation coefficient between the methods was 0.981 (95 % confidence interval: 0.975 to 0.985). Linear regression analysis demonstrated highly significant associations of carbamazepine concentrations with albumin (B = -0.300, p = 0.040), calcium (B = -0.262, p = 0.004), phosphorus (B = -0.241, p = 0.022), WBC (B = -0.288, p = <0.001), PLT (B = -0.236, p = 0.003), RBC (B = -0.257, p = 0.001), NEU% (B = -0.289, p = <0.001), LYM% (B = -0.268, p = 0.001), D vitamini (B = -0.344, p = 0.006) levels.

CONCLUSIONS

A robust, rapid, and simple method has been developed. Our study revealed that carbamazepine and its metabolite have a significant correlation and likely impact on bone metabolism, blood cell counts, serum protein, albumin levels, and electrolyte concentrations.

Human Exposure to Wastewater-Derived Pharmaceuticals in Fresh Produce: A Randomized Controlled Trial Focusing on Carbamazepine

Fresh water scarcity has led to increased use of reclaimed wastewater as an alternative and reliable source for crop irrigation. Beyond microbiological safety, concerns have been raised regarding contamination of reclaimed wastewater by xenobiotics including pharmaceuticals. This study focuses on carbamazepine, an anticonvulsant drug which is ubiquitously detected in reclaimed wastewater, highly persistent in soil, and taken up by crops. In a randomized controlled trial we demonstrate that healthy individuals consuming reclaimed wastewater-irrigated produce excreted carbamazepine and its metabolites in their urine, while subjects consuming fresh water-irrigated produce excreted undetectable or significantly lower levels of carbamazepine. We also report that the carbamazepine metabolite pattern at this low exposure level differed from that observed at therapeutic doses. This "proof of concept" study demonstrates that human exposure to xenobiotics occurs through ingestion of reclaimed wastewater-irrigated produce, providing real world data which could guide risk assessments and policy designed to ensure the safe use of wastewater for crop irrigation.

The effect of poor compliance on the pharmacokinetics of carbamazepine and its epoxide metabolite using Monte Carlo simulation

AIM

To study the effects of delayed and missed doses (poor compliance) on the pharmacokinetics of carbamazepine (CBZ) and its main active metabolite carbamazepine-10,11-epoxide (CBZE) in Chinese epilepsy patients using Monte Carlo simulation.

METHODS

CBZ and CBZE time-concentration profiles in various scenarios were generated based on a population pharmacokinetic study in Chinese epilepsy patients using Monte Carlo simulation. The scenarios included patients given multiple doses of CBZ that ranged from 100 to 300 mg three times daily or from 200 to 300 mg every 12 h. The therapeutic range of CBZ and CBZE for each scenario was estimated to assess the effect of delayed or missed doses and to design corresponding rescue regimens. Moreover, the impact of body weight, absorption rate and co-therapy with other antiepileptic drugs (phenytoin, phenobarbital and valproic acid) on the dosage recommendation was investigated in the event of poor compliance.

RESULTS

The risk for a sub-therapeutic range of CBZ and CBZE was increased in a dose-dependent manner in both two and three times daily regimens when delayed or missed doses occurred. The effects of poor compliance was less prominent on the lower daily doses compared with those on the higher daily doses. The dose recommendations, in the event of poor compliance, were time related and dose dependent. Patient body weight, absorption rate and co-therapy with phenytoin, phenobarbital and valproic acid had no significant impact on the dose recommendation.

CONCLUSION

Patients with epilepsy should take the delayed doses as soon as they remember, and partial missed doses may need to be taken near or at the next scheduled time.

Analysis of selected anticonvulsants by high performance liquid chromatography-tandem mass spectrometry

A method for the analysis of the basic antiepileptic compounds felbamate, lamotrigine, carbamazepine, carbamazepine-10,11-epoxide, gabapentin, pregabalin, levetiracetam, and oxcarbazepine monohydroxy derivative (oxcarb MHD) in human plasma is described. This protocol incorporates a simplified sample preparation step followed by quantitative high performance chromatography-tandem mass spectrometry detection of commonly prescribed and monitored anticonvulsant drugs. Since polytherapy is common in epilepsy patients, use of a multiconstituent assay can improve laboratory efficiency and reduce required analytical time.

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.

Analytical performance evaluation of ADVIA Chemistry Carbamazepine_2 assay: minimal cross-reactivity with carbamazepine 10, 11-epoxide and none with hydroxyzine or cetirizine

Carbamazepine is an anticonvulsant requiring routine therapeutic drug monitoring. Recently, Siemens Healthcare Diagnostic Division released a new carbamazepine assay: ADVIA Chemistry Carbamazepine_2 (Carbamazepine_2) for application on ADVIA analyzers. We evaluated the analytical performance of this assay as well as its potential cross-reactivities with carbamazepine 10, 11-epoxide, hydroxyzine, and cetirizine. The within-run and between-run precisions of the Carbamzepine-2 assay were <6% and limit of detection was 0.5 microg/ml using ADVIA 1800 analyzer. The assay was linear up to a carbamazepine concentration of 20.0 microg/ml. The new method compared well with a widely used carbamazepine EMIT 2000 assay on the Hitachi 917 analyzer. Using 75 patients' specimens (where carbamazepine concentrations varied from 0.5 to 21.7 microg/ml) and carbamazepine EMIT 2000 as the reference method (x-axis), we observed the following regression equation: y=1.04 x+0.32 (r=0.99). The new carbazepine_2 method was not affected by a hemoglobin concentration of 1,000 mg/dl, conjugated or unconjugated bilirubin concentration of 60 mg/dl, and triglyceride concentration of 1,000 mg/dl. In addition, this assay showed no cross-reactivity with hydroxyzine or cetirizine and demonstrated minimal cross-reactivity with carbamazepine 10, 11-epoxide. We conclude that the ADVIA Chemistry carbamazepine_2 assay has adequate precision and accuracy for routine therapeutic drug monitoring of carbamazepine in clinical laboratories.

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.

Relative proportions of serum carbamazepine and its pharmacologically active 10,11-epoxy derivative: effect of polytherapy and renal insufficiency

BACKGROUND

The proposed action mechanism and pharmacological activity of carbamazepine (CBZ) and its major metabolite, carbamazepine-10,11-epoxide (CBZE), are the same. The aim of our study was the investigation of the effect of concomitant antiepileptic treatment and renal insufficiency on the relative proportions of serum CBZ and CBZE.

METHODS

Serum trough steady-state CBZ and CBZE concentrations were determined by high-performance liquid chromatography (HPLC) in 140 epileptic patients treated with CBZ in monotherapy (n=100) and polytherapy with phenytoin, phenobarbital and valproate (n=40). The levels of CBZ were also determined using the Dade Behring enzyme multiplied immunoassay technique (EMIT). The glomerular filtration rate (GFR) was estimated from serum cystatin C using the Dade Behring nephelometric immunoassay.

RESULTS

The CBZE/CBZ and CBZ+CBZE/CBZEMIT ratios were significantly increased in 7 cases (3 in monotherapy and 4 in polytherapy) with GFR<60 mL/min/1.73m2 in relation to the patients treated in monotherapy or polytherapy having normal or mildly decreased renal function (p<0.001).

CONCLUSIONS

In patients with moderate to severe renal insufficiency the relative proportion of CBZE with respect to the parent drug is significantly increased. In these cases, the CBZ concentrations obtained using the EMIT, or other immunoassays having low CBZE cross-reactivity, may have an inadequate diagnostic efficiency.

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.

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.

Population pharmacokinetic modeling of steady state clearance of carbamazepine and its epoxide metabolite from sparse routine clinical data

OBJECTIVE

To develop a population pharmacokinetic model to evaluate the effects of variety of covariates on clearance of carbamazepine (CBZ) and its main metabolite carbamazepine-10,11-epoxide (CBZE) in Chinese population.

METHODS

Serum samples at steady trough state (n = 459) were collected prospectively from 408 compliant outpatients during their routine clinical care. CBZ and CBZE concentrations were simultaneously determined by high performance liquid chromatography. Population clearance (CL) of CBZ and CBZE were estimated by non-linear mixed effect modeling and NONMEM program with a one-compartment model of first-order absorption and elimination.

RESULTS

Total body weight (TBW), dose and concomitant medication were all important determinants of CL of CBZ and CBZE. The final regression model for CBZ was: where VPA = 1 for patients comedicated with valproic acid and its dose greater than 18 mg/kg, otherwise VPA = 0; PHT = 1 for patients comedicated with phenytoin, otherwise PHT = 0; PB = 1 for patients comedicated with phenytoin, otherwise PB = 0. The final regression CL model for the CBZE was: where VPA = 1 for patients comedicated with valproic acid, otherwise VPA = 0.

CONCLUSION

The current models, which describe CL of CBZ and CBZE in terms of patient specific details, can be used as a reference to optimize CBZ therapy in Chinese epilepsy patients.

Therapeutic drug monitoring of old and newer anti-epileptic drugs

The aim of the present paper is to provide information concerning the setting up and interpretation of therapeutic drug monitoring (TDM) for anti-epileptic drugs. The potential value of TDM for these drugs (including carbamazepine, clobazam, clonazepam, ethosuximide, felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, pheneturide, phenobarbital, phenytoin, primidone, tiagabine, topiramate, valproic acid, vigabatrin and zonisamide) is discussed in relation to their mode of action, drug interactions and their pharmacokinetic properties. The review is based upon available literature data and on observations from our clinical practice. Up until approximately 15 years ago anti-epileptic therapeutics were restricted to a very few drugs that were developed in the first half of the 20th century. Unfortunately, many patients were refractory to these drugs and a new generation of drugs has been developed, mostly as add-on therapy. Although the efficacy of the newer drugs is no better, there is an apparent improvement in drug tolerance, combined with a diminished potential for adverse drug interactions. All new anticonvulsant drugs have undergone extensive clinical studies, but information on the relationship between plasma concentrations and effects is scarce for many of these drugs. Wide ranges in concentrations have been published for seizure control and toxicity. Few studies have been undertaken to establish the concentration-effect relationship. This review shows that TDM may be helpful for a number of these newer drugs.