Therapeutic Drug Monitoring of Second- and Third-Generation Antiepileptic Drugs: Insights From a College of American Pathologists Proficiency Testing Survey

Implementation and validation of a 24/7 system for the monitoring of antiepileptic drugs

Background

Epilepsy is a common neurological disorder associated with seizures that impact patients' quality of life. Treatment includes antiepileptic drugs (AEDs), each effective only at a specific dose, making continuous therapeutic drug monitoring (TDM) useful in clinical cases under inpatient conditions. Conventional liquid chromatography-tandem mass spectrometry (LC-MS/MS) lacks automation for 24/7 operation, limiting clinical applicability. This study validates a fully automated 24/7 AED monitoring system using the Clinical Laboratory Automated Sample Preparation Module 2030 (CLAM-2030).

Methods

The method was validated according to U.S. Food and Drug Administration (FDA) and European Medicines Agency (EMA) guidelines by evaluating linearity, precision, accuracy, carry over, matrix effects, and calibration stability. Twenty-six AEDs were quantified in plasma using multiple reaction monitoring (MRM) transitions in positive and negative electrospray ionization modes. Sample preparation was fully automated: 20 μL methanol was used to wet the column, followed by 20 μL internal standard and 100 μL acetonitrile for protein precipitation. The supernatant was filtered and injected directly into the LC system. Chromatographic separation was achieved within 4.5 min using a C18 column (2.1 × 50 mm, 2.7 μm) under gradient conditions with a mobile phase of 0.2 mM ammonium formate and 0.002% formic acid.

Results

The method demonstrated excellent linearity over the validated concentration ranges (R 2 > 0.99 for all analytes). Within-run imprecision was <15% at the lower limit of quantitation (LLOQ), while between-run imprecision was <10% for most AEDs. Accuracy was within ±10% of nominal concentrations at all quality control (QC) levels. Matrix effects were within acceptable limits (<30% variation) for 23 of 26 analytes, with compensatory corrections applied for carbamazepine-D10, felbamate-D4, and levetiracetam-D6. Carry over was negligible [<2% for all AEDs except retigabine and N-desmethylselegiline (NDMS), which remained below 6.5%]. Calibration stability was maintained over 5 days with concentration and peak area variation <10%. An interlaboratory comparison (ring test) showed a relative standard deviation <20% for all analytes.

Conclusion

This study establishes a robust, fully automated, high-throughput method for continuous AED monitoring in the clinical setting. The CLAM-2030-LCMS-8060NX system enables reliable 24/7 TDM with minimal technical expertise, ensuring optimized AED therapy and improved patient outcomes.

Therapeutic Drug Monitoring of 6 New-Generation Antiseizure Medications Using a Mass Spectrometry Method: Analysis of 2-Year Experience in a Large Cohort of Korean Epilepsy Patients

CONTEXT.—

New-generation antiseizure medications (ASMs) are increasingly prescribed, and therapeutic drug monitoring (TDM) has been proposed to improve clinical outcome. However, clinical TDM data on new-generation ASMs are scarce.

OBJECTIVE.—

To develop and validate a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for therapeutic drug monitoring (TDM) of 6 new-generation ASMs in serum and analyze the clinical TDM data from a large cohort of Korean patients with epilepsy.

DESIGN.—

Stable isotope-labeled internal standards were added to protein precipitations of serum. One microliter of sample was separated on an Agilent Poroshell EC-C18 column, and lacosamide, perampanel, gabapentin, pregabalin, vigabatrin, and rufinamide were simultaneously quantified by Agilent 6460 triple-quad mass spectrometer in multiple-reaction monitoring mode. Linearity, sensitivity, precision, accuracy, specificity, carryover, extraction recovery, and matrix effect were evaluated. TDM data of 458 samples from 363 Korean epilepsy patients were analyzed.

RESULTS.—

The method was linear with limit of detection less than 0.05 μg/mL in all analytes. Intraassay and interassay imprecisions were less than 5% coefficient of variation. Accuracy was within ±15% bias. Extraction recovery ranged from 85.9% to 98.8%. A total of 88% (403 of 458) were on polypharmacy, with 29% (118 of 403) using concomitant enzyme inducers. Only 38% (175 of 458) of the concentrations were therapeutic, with 53% (244 of 458) being subtherapeutic. Drug concentration and concentration-to-dose ratio were highly variable among individuals for all 6 ASMs.

CONCLUSIONS.—

A simple and rapid LC-MS/MS method for TDM of 6 ASMs was developed and successfully applied to clinical practice. These large-scale TDM data could help establish an effective monitoring strategy for these drugs.

Clinical impact of therapeutic drug monitoring for newer anti-seizure medications in patients with epilepsy: A real-world observation study

BACKGROUND

The clinical value of therapeutic drug monitoring (TDM) for newer anti-seizure medications (ASMs) remains uncertain. This study aimed to assess the impact of newer ASM TDM on clinical decision making in patients with epilepsy.

METHODS

We retrospectively identified all plasma requests for newer ASM level measurement as part of routine clinical management in the outpatient departments of seven medical institutes across Taiwan between September 2016 and May 2019. Data collected from reviewed medical records included clinical and medication details, indications for TDM requests, test results, interpretation, and impact on patient management.

RESULTS

A total of 682 visits with 1051 plasma samples were included. The most frequently analyzed ASMs were levetiracetam (36.1%), oxcarbazepine (18.4%), and lamotrigine (12.0%). Reasons for TDM included poorly controlled seizures (55.3%), concerns about drug-drug interactions (12.3%), and suspicion of drug overdose (10.6%). 68.8% of samples were within the orienting therapeutic range, even for patients with poorly controlled seizures. TDM for non-adherence concerns showed 54.3% below the orienting therapeutic range, while ASM-related adverse events assessment only 8.9% showed levels exceeding the orienting therapeutic range. Following TDM results, 64.2% of cases had medication adjustments, mainly dosage increases. Overall, 55.9% of newer ASM TDM visits showed improved outcomes, including reduced seizures (47.5%) and fewer ASM-related side effects (8.4%).

CONCLUSIONS

These findings suggest that appropriate utilization of TDM for newer ASMs provides clinical benefits in adjunct to complement clinical decision making in the management of epilepsy patients in a real-world clinical setting.

Role of Chalcogenides in Sensitive Therapeutic Drug Monitoring Using Laser Desorption and Ionization

This study investigates the applicability of six transition metal dichalcogenides to efficient therapeutic drug monitoring of ten antiepileptic drugs using laser desorption/ionization-mass spectrometry. We found that molybdenum ditelluride and tungsten ditelluride are suitable for the sensitive quantification of therapeutic drugs. The contribution of tellurium to the enhanced efficiency of laser desorption ionization was validated through theoretical calculations utilizing an integrated model that incorporates transition-metal dichalcogenides and antiepileptic drugs. The results of our theoretical calculations suggest that the relatively low surface electron density for the tellurium-containing transition metal dichalcogenides induces stronger Coulombic interactions, which results in enhanced laser desorption and ionization efficiency. To demonstrate applicability, up to 120 patient samples were analyzed to determine drug concentrations, and the results were compared with those of immunoassay and liquid chromatography-tandem mass spectrometry. Agreements among these methods were statistically evaluated using the Passing-Bablok regression and Bland-Altman analysis. Furthermore, our method has been shown to be applicable to the simultaneous detection and multiplexed quantification of antiepileptic drugs.

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

OBJECTIVES

To describe and validate an isotope dilution-liquid chromatograph-tandem mass spectrometry (ID-LC-MS/MS) based reference measurement procedure (RMP) for zonisamide to accurately measure serum and plasma concentrations.

METHODS

Quantitative nuclear magnetic resonance (qNMR) spectroscopy was employed to determine the absolute content of the reference material used in order to establish traceability to SI units. Separation of zonisamide from known or unknown interferences was performed on a C8 column. For sample preparation a protocol based on protein precipitation in combination with a high dilution step was established. Assay validation and determination of measurement uncertainty were performed 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 was proven to be highly selective and specific with no evidence of a matrix effect, allowing for quantification of zonisamide within the range of 1.50-60.0 μg/mL. Intermediate precision was <1.4 % and repeatability CV ranged from 0.7 to 1.2 % over all concentration levels. The relative mean bias ranged from 0.0 to 0.8 % for native serum levels and from 0.2 to 2.0 % for Li-heparin plasma levels. The measurement uncertainties for single measurements and target value assignment ranged from 1.1 to 1.4 % and 0.8-1.0 %, respectively.

CONCLUSIONS

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

Simultaneous monitoring of seven antiepileptic drugs by dried blood spot and dried plasma spot sampling: method validation and clinical application of a LC-MS/MS-based technique

Alternative blood sampling strategy can enhance the application of therapeutic drug monitoring (TDM), then improve precision therapy and medication compliance. In developing nations, alternative sampling strategy that allows self-sampling and room temperature transport is especially important. This study validates the use of dried blood spot (DBS) and dried plasma spot (DPS) sampling along with liquid chromatography-tandem mass spectrometry (LC-MS/MS) for analyzing seven common antiepileptic drugs (AEDs) (phenytoin, lamotrigine, levetiracetam, topiramate, carbamazepine, oxcarbazepine and its active metabolite 10,11-dihydro-10-hydroxy carbamazepine) and evaluates their applicability to clinical practice. Following simple protein precipitation with acetonitrile, the AEDs were separated on a C18 column by gradient elution with a mobile phase consisting of acetonitrile-water-0.1% formic acid at a flow rate of 0.65 mL/min. The method provided linear analysis over the tested concentration ranges, with a total run time of 7 min. Intra- and inter-assay precision for all quality controls were ≤12% with accuracies of 85.9%-113%. The average extraction efficiencies were 69.0%-92.4% for DBS and 65.9%-96.5% for DPS, and no significant matrix effects were observed. The AEDs were stable in all samples for seven days at room temprature and 40°C. There was good correlation between the dry and wet plasma concentrations with greater accuracy for DPS compared to DBS indicating that alternative sampling strategy using DBS and DPS are suitable for monitoring the concentrations of AEDs with satisfied performance and logistical advantages.

Quantitative LC-MS/MS Method for the Simultaneous Measurement of Six Antiepileptics and Pentobarbital in Human Serum

Antiepileptic drugs (AEDs) are a chemically diverse group of medications that are used to control seizures and different clinical forms of epilepsy. AEDs can be used as single agents but are commonly administered in combination, as a multi-drug regimen. AEDs have narrow therapeutic windows. Therapeutic ranges may not be properly defined, and symptoms of toxic serum concentrations may include increased frequency of seizures, as seen when AED concentrations are subtherapeutic. Pentobarbital, a barbiturate, is a potent anti-seizure medication, but it is also used in the treatment of head injury. Therapeutic drug monitoring (TDM) is required for optimal treatment of epilepsy. The method presented here is designed to measure serum concentrations of six commonly administered antiepileptic drugs (levetiracetam (Keppra), lamotrigine, lacosamide, 10-hydroxycarbazepine (oxcarbazepine metabolite), topiramate, zonisamide) and that of pentobarbital by LC-MS/MS. Liquid-liquid sample extraction is followed by reversed-phase chromatography using biphenyl HPLC column and gradient elution. Two MRM transitions are monitored for each drug, and their heavy isotope labeled internal standards. Six-point calibration curve is generated with each batch of analysis for quantitation of AEDs. The method's AMR covers the clinically relevant concentration range for each AED. The method has <10% CV throughout the AMR, is free of matrix effect commonly found in clinical samples, and is free from cross reactivity by other AEDs.

Overview of therapeutic drug monitoring and clinical practice

With the rapid development of clinical pharmacy in China, therapeutic drug monitoring (TDM) has become an essential tool for guiding rational clinical drug use and is widely concerned. TDM is a tool that combines pharmacokinetic and pharmacodynamic knowledge to optimize personalized drug therapy, which can improve treatment outcomes, reduce drug-drug toxicity, and avoid the risk of developing drug resistance. To effectively implement TDM, accurate and sophisticated analytical methods are required. By researching the literature published in recent years, we summarize the types of commonly monitored drugs, therapeutic windows, and clinical assays and track the trends and hot spots of therapeutic drug monitoring. The purpose is to provide guidelines for clinical blood drug concentration monitoring, to implement individualized drug delivery programs better, to ensure the rational use of drugs for patients, and to provide a reference for the group to carry out related topics in the future.

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

OBJECTIVES

To develop an isotope dilution-liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based candidate reference measurement procedure (RMP) for levetiracetam quantification in human serum and plasma.

METHODS

Quantitative nuclear magnetic resonance spectroscopy (qNMR) was used to characterize the RMP material to ensure traceability to SI units. To quantify levetiracetam, an LC-MS/MS method was optimized using a C8 column for chromatographic separation following protein-precipitation-based sample preparation. Spiked matrix samples of serum and plasma were used to test selectivity and specificity. Matrix effects were determined by performing a post-column infusion experiment and comparing standard line slopes. Precision and accuracy were evaluated over 5 days. Measurement uncertainty was evaluated according to the Guide to the Expression of Uncertainty in Measurement (GUM).

RESULTS

The RMP was proven to be highly selective and specific with no evidence of a matrix effect, allowing for quantification of levetiracetam within the range of 1.53-90.0 μg/mL. Intermediate precision was <2.2% and repeatability was 1.1-1.7% across all concentrations. The relative mean bias ranged from -2.5% to -0.3% across all levels and matrices within the measuring range. Diluted samples were found with a mean bias ranging from -0.1 to 2.9%. The predefined acceptance criterion for measurement uncertainty was met and determined for individual measurements independently of the concentration level and sample type to be ≤4.0% (k=2).

CONCLUSIONS

We present a novel LC-MS/MS)-based candidate RMP for levetiracetam in human serum and plasma. Its expanded measurement uncertainty of ≤4.0% meets the clinical needs in levetiracetam monitoring. Utilizing qNMR to characterize levetiracetam reference materials allowed metrological traceability to SI units.

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

OBJECTIVES

Topiramate is an antiepileptic drug (AED) used for the monotherapy or adjunctive treatment of epilepsy and for the prophylaxis of migraine. It has several pharmacodynamic properties that contribute to both its clinically useful properties and observed adverse effects. Accurate measurement of its concentration is therefore essential for dose adjustment/optimisation of AED therapy. Our aim was to develop and validate a novel reference measurement procedure (RMP) for the quantification of topiramate in human serum and plasma.

METHODS

An isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS) method in combination with a protein-precipitation-based sample preparation allows for quantification of topiramate in human serum and plasma. To assure traceability to SI units, quantitative nuclear magnetic resonance (qNMR) was applied to characterize the reference material used as primary calibrator for this RMP. Matrix effects were determined by performing a post-column infusion experiment and comparing standard line slopes. Accuracy and precision was evaluated performing an extensive five day precision experiment and measurement uncertainty was evaluated according Guide to the Expression of Uncertainty in Measurement (GUM).

RESULTS

The method enabled topiramate quantification within the range of 1.20-36.0 μg/mL without interference from structurally related compounds and no evidence of a matrix effect. Intermediate precision was ≤3.2 % and repeatability was 1.4-2.5 % across all concentration levels. The relative mean bias was -0.3 to 3.5 %. Expanded measurement uncertainties for target value assignment (n=6) were found to be ≤2.9 % (k=2) independent of the concentration level and the nature of the sample.

CONCLUSIONS

In human serum and plasma, the RMP demonstrated high analytical performance for topiramate quantification and fulfilled the requirements on measurement uncertainty. Traceability to SI units was established by qNMR content determination of the topiramate, which was used for direct calibration of the RMP. This RMP is, therefore, fit for purpose for routine assay standardization and clinical sample evaluation.

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

OBJECTIVES

To describe and validate a reference measurement procedure (RMP) for gabapentin, employing quantitative nuclear magnetic resonance (qNMR) spectroscopy to determine the absolute content of the standard materials in combination with isotope dilution-liquid chromatograph-tandem mass spectrometry (ID-LC-MS/MS) to accurately measure serum and plasma concentrations.

METHODS

A sample preparation protocol based on protein precipitation in combination with LC-MS/MS analysis using a C8 column for chromatographic separation was established for the quantification of gabapentin. Assay validation and determination of measurement uncertainty were performed according to guidance from the Clinical and Laboratory Standards Institute, the International Conference on Harmonization, and the Guide to the expression of uncertainty in measurement. ID-LC-MS/MS parameters evaluated included selectivity, specificity, matrix effects, precision and accuracy, inter-laboratory equivalence, and uncertainty of measurement.

RESULTS

The use of qNMR provided traceability to International System (SI) units. The chromatographic assay was highly selective, allowing baseline separation of gabapentin and the gabapentin-lactam impurity, without observable matrix effects. Variability between injections, preparations, calibrations, and days (intermediate precision) was <2.3%, independent of the matrix, while the coefficient of variation for repeatability was 0.9-2.0% across all concentration levels. The relative mean bias ranged from -0.8-1.0% for serum and plasma samples. Passing-Bablok regression analysis indicated very good inter-laboratory agreement; the slope was 1.00 (95% confidence interval [CI] 0.98 to 1.03) and the intercept was -0.05 (95% CI -0.14 to 0.03). Pearson's correlation coefficient was ≥0.996. Expanded measurement uncertainties for single measurements were found to be ≤5.0% (k=2).

CONCLUSIONS

This analytical protocol for gabapentin, utilizing traceable and selective qNMR and ID-LC-MS/MS techniques, allows for the standardization of routine tests and the reliable evaluation of clinical samples.

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

OBJECTIVES

We developed an isotope dilution (ID)-liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based candidate reference measurement procedure (RMP) for lamotrigine in human serum and plasma, using quantitative nuclear magnetic resonance-characterized reference standards to ensure traceability to the International System of Units.

METHODS

A sample preparation protocol based on protein precipitation combined with LC-MS/MS analysis using a C18 column for chromatographic separation was established for the quantification of lamotrigine in human serum and plasma. Assay validation was performed according to current guidelines. Spiked serum and plasma samples were used to assess selectivity and specificity; a post-column infusion experiment and comparison of standard line slopes were performed to ascertain possible matrix effects. Precision and accuracy were determined in a 5 days validation experiment. Measurement uncertainty was determined per the Guide to the Expression of Uncertainty in Measurement.

RESULTS

The method allowed the quantification of lamotrigine in serum and plasma in a range of 0.600-24.0 μg/mL without any observable matrix effects. The relative mean bias (n=6) ranged from 1.7 to 3.7%; intermediate precision, including variances in between-day, -calibration, and -injection, was ≤2.4%, independent of the level and matrix. Total measurement uncertainty for a single measurement was ≤2.6%; expanded uncertainty was ≤5.2% (coverage factor k=2).

CONCLUSIONS

This candidate RMP based on ID-LC-MS/MS provides a traceable and reliable platform for the standardization of routine assays and the evaluation of clinical samples.

An LC-ESI-MS/MS assay for the therapeutic drug monitoring of 15 anti-seizure medications in plasma of children with epilepsy

Oral anti-seizure medications (ASMs) is the preferred option for the clinical treatment of epilepsy. Therapeutic Drug Monitoring (TDM) has become an important means of individualized treatment of epilepsy. A sensitive, accurate and rapid LC-ESI-MS/MS method was developed and validated for the simultaneous determination of 15 ASMs in human plasma (carbamazepine, gabapentin, prebaglin, phenytoin, zonisamide, oxcarbazepine, tiagabine, lamotrigine, topiramate, phenobarbital, lacosamide, primidone, 10,11-dihydro-10-hydroxycarbamazepine, ethosuximide, and levetiracetam). The sample preparation procedure was an one-step protein precipitation with methanol (MeOH). The mass detection was performed in ionization polarity switching mode (positive-negative-positive) using multiple reaction monitoring mode. A "boot-shaped" gradient elution program was applied to separate and concentrate those target analytes resulting in symmetrical peak shapes within 10 min, without endogenous interference. The method showed great linearity over their concentration ranges with acceptable correlation coefficients (0.9966~0.9996). The precision and accuracy values for intra- and inter-assays were within ±15%. Consequently, the method was successfully implemented on pediatric patients undergoing mono- or polytherapy for epilepsy and provided timely concentration results to ordering clinicians.

Data on the relationship between lamotrigine and levetiracetam serum/plasma levels and toxicity: Experience at an academic medical center

Lamotrigine and levetiracetam are second-generation anti-epileptic drugs used for the management of seizure disorders and some other medical conditions. In the related research article using retrospective data from an academic medical center, we analyzed 5046 samples originating from 1930 unique patients that had lamotrigine drug levels performed on serum/plasma and 4359 samples from 2451 patients that had levetiracetam drug levels performed. The data in this article provides the patient demographic, clinical location at time of drug level, and specific lamotrigine or levetiracetam serum/plasma drug level for all patients. For those instances with lamotrigine drug level greater than 14.0 mg/L or levetiracetam drug level of 80 mg/L or higher, additional data from chart review includes: indication for ordering the drug level, two main presenting signs or symptoms at time of drug level, timing of drug level (random, trough, peak, or unknown), changes in drug dosing following the drug level, concomitant therapy with valproic acid (lamotrigine only), and details related to drug overdose (if applicable). The analyzed data is provided in the supplementary tables included in this article. Volumes of test ordering by year is included in a figure. The dataset reported is related to the research article entitled "Correlation of Elevated Lamotrigine and Levetiracetam Serum/Plasma Levels with Toxicity: A Long-Term Retrospective Review at an Academic Medical Center" [K. E. Wood, K. L. Palmer, M.D. Krasowski, Correlation of elevated lamotrigine and levetiracetam serum/plasma levels with toxicity: A long-term retrospective review at an academic medical center, Toxicol. Rep. (2021) 8:1592-1598].

Correlation of elevated lamotrigine and levetiracetam serum/plasma levels with toxicity: A long-term retrospective review at an academic medical center

Lamotrigine and levetiracetam are widely used second-generation anti-epileptic drugs. Existing literature indicates that overdose of either drug is typically benign, but neurologic and cardiac toxicity can occur in some cases. In this retrospective study, we analyzed a large dataset of serum/plasma drug levels for lamotrigine and levetiracetam. The data covered 1,930 unique patients (5,046 levels) for lamotrigine and 2,451 patients (4,359 levels) for levetiracetam. We performed detailed chart review on all patients with one or more lamotrigine levels greater than 14.0 mg/L (293 unique patients) and all patients with one or more levetiracetam levels of 80 mg/L or higher (106 unique patients). No deaths directly attributable to lamotrigine or levetiracetam toxicity were reported. For cases with lamotrigine levels greater than 14.0 mg/L, the majority of patients were asymptomatic (55.3 %, n = 162). The most common presenting symptoms were ataxia (14.3 %, n = 42), seizures (14.0 %, n = 41), dizziness (11.9 %, n = 35), and altered mental status (11.6 %, n = 34). There were 12 overdoses (11 intentional) involving lamotrigine, all of which presented with either altered mental status (n = 8) or seizures (n = 4). The highest estimated dose reportedly ingested was 20 g. Cardiac toxicity was observed in two cases involving intentional overdose of lamotrigine. For patients with levetiracetam serum/plasma levels of 80 mg/L or higher, 48 patients (45.3 %) were asymptomatic. Symptomatic patients most commonly presented with seizures (31.1 %, n = 33) and altered mental status (15.1 %, n = 16), and none showed cardiac symptoms. There were only two cases involving intentional levetiracetam overdose, one of which presented with altered mental status after ingestion of 45 g and the other asymptomatic after ingestion of 6 g. Overall, our data is consistent with previous investigations that lamotrigine and levetiracetam toxicity most typically presents with neurologic symptoms and rarely cardiac arrhythmias. Approximately half of the patients with elevated lamotrigine or levetiracetam drug levels are asymptomatic.