Clinical Pharmacokinetics of New-Generation Antiepileptic Drugs at the Extremes of Age

Population Pharmacokinetics of Topiramate in Patients with Epilepsy Using Nonparametric Modeling

BACKGROUND

Topiramate (TPM) is used for the treatment of various epileptic seizures and the prevention of migraine. This study aimed to develop a population pharmacokinetic model and identify covariates that influence TPM behavior in patients with epilepsy in Kuwait.

METHODS

Data were collected retrospectively from 108 patients (2 years old and above) with epilepsy who were treated with oral TPM and 174 TPM blood samples from 3 hospitals in Kuwait from 2009 to 2016. Data were randomly divided into 2 groups for model development and validation. The population pharmacokinetic model was built using the nonparametric modeling algorithm (Pmetrics). The model was evaluated internally through the visual predictive check method and externally using a new data set.

RESULTS

A 1-compartment model with first-order elimination fitted the data well. Covariates showing a significant effect on the elimination rate constant were renal function and coadministration of carbamazepine (CBZ). The mean estimated clearance was 2.11 L/h; this was 50% higher for patients coadministered with CBZ. Age and sex were essential covariates for the volume of distribution (V). The visual predictive check of the final model could predict the measured concentrations. External validation further confirmed the favorable predictive performance of the model with low bias and imprecision for predicting the concentration in a particular population.

CONCLUSIONS

TPM elimination was increased with CBZ coadministration and was affected by renal function. Meanwhile, age and sex were the main predictors for V. The predictive performance of the final model proved to be valid internally and externally.

Efficacy and tolerability of oxcarbazepine in the treatment of focal epilepsy in neonates and infants under 3 months of age: A single-center retrospective analysis

OBJECTIVE

The neonatal and infantile period is the age group with the highest incidence of epilepsy, in which gene variants in sodium and potassium channels are an important etiology, so the sodium channel blocker class of antiseizure medications may be effective in the treatment of early onset epilepsy. This study aimed to summarize the efficacy and tolerability of oxcarbazepine (OXC) in the treatment of focal epilepsy in neonates and infants under 3 months of age.

METHODS

A retrospective analysis of children with focal epilepsy onset within 3 months of age and treated with OXC in a tertiary pediatric epilepsy center in China was conducted. The efficacy, tolerability and influencing factors of OXC were evaluated.

RESULTS

A total of 50 patients were enrolled, with a median age of epilepsy onset of 11.5 (2, 42) days. There were 32 cases of early infantile developmental and epileptic encephalopathy, 10 cases of self-limited neonatal or neonatal-infantile epilepsy, and 8 cases of focal epilepsy that could not be classified as epileptic syndrome. The median age of application of OXC was 47 (31, 66) days. The median follow-up time was 16.5 (10, 25) months, with 7 deaths. Thirty-eight cases (76.0 %) were effective with OXC treatment, including 28 cases (56.0 %) achieved seizure freedom. Of the 34 cases whose pathogenesis involved genetic factors, 19 cases with sodium/ potassium channel gene variants had higher effective and seizure-free rates than those with other gene variants. The most common adverse event was transient hyponatremia. 2 cases had rash and 2 cases had abnormal electrocardiogram, 3 of which discontinued OXC.

SIGNIFICANCE

This single-center retrospective study suggests that OXC is effective and tolerable for the treatment of focal epilepsy in neonates and infants under 3 months of age. The efficacy of OXC is better in patients with sodium/ potassium channel gene variants.

Analysis of influencing factors on monohydroxylated derivative of oxcarbazepine plasma concentration in children with epilepsy

PURPOSE

This study aimed to investigate the factors affecting the plasma concentration of monohydroxylated derivative (MHD) of oxcarbazepine (OXC) in children with epilepsy.

METHODS

We recruited 125 children with epilepsy who received OXC monotherapy. Among them, 16 single nucleotide polymorphisms were detected by MassARRAY genotyping technology to evaluate the influence of related factors on the plasma concentration of OXC monotherapy. MHD is the main active metabolite of OXC, and its plasma concentration was measured by high-performance liquid chromatography (HPLC).

RESULTS

Bivariate correlation analysis revealed that concentration-dose ratio (CDR) increased with weight, and the corresponding maintenance dose decreased with weight (r=0.317, P=0.001 for CDR; r=-0.285, P=0.000 for OXC maintenance dose). The duration of seizure was found to be associated with CDR (0.90 ± 0.36 vs 0.74 ± 0.26 μg·kg/mg/mL for ≥6 years vs <1 year, P=0.028; 0.90 ± 0.36 vs 0.64 ± 0.21 μg·kg/mg/mL for ≥6 years vs 1-3 years, P=0.004; 0.90 ± 0.36 vs 0.69 ± 0.18 μg·kg/mg/mL for ≥6 years vs 3-6 years, P=0.031). The CDR of patients with ABCB1 rs1045642 mutation homozygous GG type is higher than heterozygous AG type (0.79 ± 0.30 vs 0.68 ± 0.20 μg·kg/mg/mL for AG vs GG, P=0.032).

CONCLUSION

This study clarified the association of weight, duration of seizure, and gene polymorphisms of ABCB1 rs1045642 with MHD plasma concentration in children with epilepsy.

Population pharmacokinetics of oxcarbazepine: a systematic review

INTRODUCTION

Oxcarbazepine is commonly used as first-line treatment for partial and generalized tonic-clonic seizures. Owing to the high pharmacokinetic variability, several population pharmacokinetic models have been developed for oxcarbazepine to explore potential covariates that affect its pharmacokinetic variation.

AREAS COVERED

This review summarizes the published population pharmacokinetic studies of oxcarbazepine in children and adults available in PubMed and Embase databases. The quality of the retrieved studies was evaluated, and significant covariates that may have an impact on the dosage regimen of oxcarbazepine were explored.

EXPERT OPINION

The pharmacokinetics of oxcarbazepine was founded to be affected by body weight and co-administration with enzyme inducers. Pediatric patients require a higher dose per kilogram than adults because children generally have a higher clearance than adults. Moreover, to maintain the target concentration, patients co-administrate with enzyme inducers need a higher dose than monotherapy due to higher clearance in those patients. Because limited information is available for exposure-response relationship, additional pharmacokinetic/pharmacodynamics investigations of oxcarbazepine need to be conducted to optimize the dosage regimen in clinical practice.

Clinical Management of Drug Resistant Epilepsy: A Review on Current Strategies

Drug resistant epilepsy (DRE) is defined as the persistence of seizures despite at least two syndrome-adapted antiseizure drugs (ASD) used at efficacious daily dose. Despite the increasing number of available ASD, about a third of patients with epilepsy still suffer from drug resistance. Several factors are associated with the risk of evolution to DRE in patients with newly diagnosed epilepsy, including epilepsy onset in the infancy, intellectual disability, symptomatic epilepsy and abnormal neurological exam. Pharmacological management often consists in ASD polytherapy. However, because quality of life is driven by several factors in patients with DRE, including the tolerability of the treatment, ASD management should try to optimize efficacy while anticipating the risks of drug-related adverse events. All patients with DRE should be evaluated at least once in a tertiary epilepsy center, especially to discuss eligibility for non-pharmacological therapies. This is of paramount importance in patients with drug resistant focal epilepsy in whom epilepsy surgery can result in long-term seizure freedom. Vagus nerve stimulation, deep brain stimulation or cortical stimulation can also improve seizure control. Lastly, considering the effect of DRE on psychologic status and social integration, comprehensive care adaptations are always needed in order to improve patients' quality of life.

Dosing Recommendations for Lamotrigine in Children: Evaluation Based on Previous and New Population Pharmacokinetic Models

Lamotrigine is a broad-spectrum antiepileptic drug with high interindividual variability in serum concentrations in children. The aims of this study were to evaluate the predictive performance of pediatric population pharmacokinetic (PPK) models published on lamotrigine, to build a new model with our monitoring data and to evaluate the current recommended doses. A validation cohort included patients treated with lamotrigine who had a serum level assayed during therapeutic drug monitoring (TDM). PPK models published in the literature were first applied to the validation cohort. We assessed their predictive performance using mean prediction errors, root mean squared errors, and visual predictive checks. A new model was then built using the data. Dose simulations were performed to evaluate the doses recommended. We included 270 lamotrigine concentrations ranging from 0.5 to 17.9 mg/L from 175 patients. The median (range) age and weight were 11.8 years (0.8-18 years) and 32.7 kg (8-110 kg). We tested 6 PPK models; most had acceptable bias and precision but underestimated the variability of the cohort. We built a 1-compartment model with first-order absorption and elimination, allometric scaling, and effects of inhibitor and inducer comedications. In our cohort, 22.6% of trough concentrations were below 2.5 mg/L. In conclusion, we proposed a PPK model that can be used for TDM of lamotrigine in children. In our population, a high percentage of children had low trough concentrations of lamotrigine. As the intervals of recommended doses are large, we suggest aiming at the higher range of doses to reach the target concentration.

Retrospective Analysis of Pediatric and Adult Populations Using an LC-MS/MS Method for Oxcarbazepine/Eslicarbazepine Metabolite

BACKGROUND

Therapeutic drug monitoring of anti-epileptic drugs is important to manage seizure control in patients with epilepsy. Oxcarbazepine is a second-generation anti-epileptic drug approved for use in pediatric patients, and eslicarbazepine acetate is a newer generation drug used as adjunctive therapy and monotherapy for partial-onset (focal) seizures. While several second and third generation anti-epileptic drugs have broader therapeutic efficacy in patients, these drugs can still have severe side effects and variable interpatient pharmacokinetics. Consequently, there is a need for accurate and sensitive analytical methods to support therapeutic drug monitoring.

METHODS

An assay improvement for a LC-MS/MS method was developed for the major metabolite of oxcarbazepine and eslicarbazepine, licarbazepine (MHD), using a 13C-labeled form of the compound as the internal standard. Additionally, retrospective data analysis was used to compare the distribution of results observed in adult vs pediatric patients.

RESULTS

Accuracy and linearity across the analytical measuring range of 1 to 60 µg/mL was acceptable. Inter- and intra-run precision was less than 6% at 3 concentrations tested. The limit of detection was determined to be 0.5 µg/mL. Significant interference from hemolysis, icterus, lipemia, or 187 other potential interferences was not detected.

CONCLUSIONS

The improved assay for MHD was appropriate for clinical use. Retrospective data analysis showed that pediatric and adult patients had a similar distribution of oxcarbazepine/eslicarbazepine metabolite concentrations in serum.

Tacrolimus treatment in childhood refractory nephrotic syndrome: A retrospective study on efficacy, therapeutic drug monitoring, and contributing factors to variable blood tacrolimus levels

Tacrolimus, an immunosuppressive drug, was recommended by the 2012 KDIGO guidelines to treat nephrotic syndrome (NS) in children and adults. However, it has high interpatient pharmacokinetic variability and exposure levels should be monitored, although there are no specified target concentrations. This retrospective study aimed to review efficacy and safety after concomitant treatment with tacrolimus and prednisone, and to identify factors that contribute to the variable blood-trough-concentration-to-dose (C₀/Dose) ratio in children with refractory NS (RNS). A 6-month therapy induced complete or partial remission in 95% of patients. One-year follow-up indicated a high remission rate and low nephrotoxicity. Under maintenance dosages, approximately 95% of the C₀ values were 2-7 ng/mL. Body weight (BW), age, CYP3A5 polymorphisms were the factors affecting the C₀/Dose ratio. The C₀/Dose ratio in patients with a BW of <20 kg was 1.5-fold than that in patients with BW of ≥40 kg. Moreover, the C₀/Dose ratio in patients aged 1-≤6 and 6-≤12 years was significantly lower than that in patients aged 12-≤18 years, by 25% and 48%, respectively. There were no significant association between CYP3A5 genotyping and C₀/Dose ratio in younger children (1-≤6 years), rather than older children (6-≤18 years). In conclusion, routine CYP3A5 genotyping should be considered in children aged over 6 years and exposure levels (C₀) of 2-7 ng/mL may be feasible when tacrolimus is combined with low-dose prednisone to treat childhood RNS.

Sodium valproate induced acute pancreatitis in a bipolar disorder patient: a case report

Background

Sodium valproate is one of the most widely used antiepileptics and mood stabilizers. However, this drug may induce acute pancreatitis. Few cases have been reported so far, mainly on the pediatric patients who underwent antiepileptic treatment. Hereby, we present a case of bipolar disorder with sodium valproate-induced acute pancreatitis.

Case presentation

The patient is a 54-year-old Chinese male. He was diagnosed with bipolar disorder for more than 39 years. Since the first onset of the disease, he had several relapses. The patient had had sodium valproate to stabilize mood swings for a year before the occurrence of acute pancreatitis. But he did vomit once during the inpatient care period. Then he was referred to another hospital following a notably high level of amylase. The results of computed tomography demonstrated an increased pancreatic volume and swollen peripancreatic fat tissue. As a result, the patient was diagnosed with acute pancreatitis. Unlike other cases reported in literatures, the high amylase level did not revert to normal after the withdrawal of medications. The patient was discharged from hospital with a high level of amylase, and was placed under follow-up observations.

Conclusion

Acute pancreatitis is considered as one of the idiosyncratic adverse reactions to antiepileptic drugs. Previous reports were mainly on the pediatric patients with increased propensity to idiosyncratic drug effects, or the adult chronic renal failure patients with sodium valproate-induced pancreatitis due to the retention of intermediate metabolites in their bodies. In this study, even though our patient exhibited no high risk of developing pancreatitis, he was treated for drug-induced acute pancreatitis in three hospitals. As rare as drug-induced acute pancreatitis can be, it should not be overlooked, Moreover, the mechanism of how sodium valproate induces acute pancreatitis remains unknown. Therefore, physicians need to consider the medical history of patients before prescribing this medication.

Therapeutic Drug Monitoring of Antiepileptic Drugs in Epilepsy: A 2018 Update

BACKGROUND

Antiepileptic drugs (AEDs) are the mainstay of epilepsy treatment. Since 1989, 18 new AEDs have been licensed for clinical use and there are now 27 licensed AEDs in total for the treatment of patients with epilepsy. Furthermore, several AEDs are also used for the management of other medical conditions, for example, pain and bipolar disorder. This has led to an increasingly widespread application of therapeutic drug monitoring (TDM) of AEDs, making AEDs among the most common medications for which TDM is performed. The aim of this review is to provide an overview of the indications for AED TDM, to provide key information for each individual AED in terms of the drug's prescribing indications, key pharmacokinetic characteristics, associated drug-drug pharmacokinetic interactions, and the value and the intricacies of TDM for each AED. The concept of the reference range is discussed as well as practical issues such as choice of sample types (total versus free concentrations in blood versus saliva) and sample collection and processing.

METHODS

The present review is based on published articles and searches in PubMed and Google Scholar, last searched in March 2018, in addition to references from relevant articles.

RESULTS

In total, 171 relevant references were identified and used to prepare this review.

CONCLUSIONS

TDM provides a pragmatic approach to epilepsy care, in that bespoke dose adjustments are undertaken based on drug concentrations so as to optimize clinical outcome. For the older first-generation AEDs (carbamazepine, ethosuximide, phenobarbital, phenytoin, primidone, and valproic acid), much data have accumulated in this regard. However, this is occurring increasingly for the new AEDs (brivaracetam, eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, perampanel, piracetam, pregabalin, rufinamide, stiripentol, sulthiame, tiagabine, topiramate, vigabatrin, and zonisamide).

Topiramate Blood Levels During Polytherapy for Epilepsy in Children

BACKGROUND

The therapeutic range of topiramate (TPM) blood level is not set because the efficacy and safety are not considered to be related to the level. However, the therapeutic target without side effects is necessary, so the optimal range of TPM blood level was analyzed in this study.

STUDY QUESTION

This study was conducted to evaluate the efficacy of TPM over 2 years and the utility of measuring blood levels of TPM during the follow-up of epileptic patients.

STUDY DESIGN

Thirty patients (18 males, 12 females; age range, 6 months-15 years) were treated with TPM for epilepsy. The initial dosage of TPM was 1-3 mg·kg·d. If the effect proved insufficient after 2 weeks, the dosage was increased to 4-9 mg·kg·d.

MEASURES AND OUTCOMES

Blood levels of TPM were measured by liquid chromatography-tandem mass spectrometry at 1, 6, 12, and 24 months after levels reached steady state. The efficacy of TPM was evaluated by the reduction in epileptic seizure rate (RR) at the time of blood sampling. Statistical analysis was performed using the Mann-Whitney U test.

RESULTS

A positive correlation was seen between blood levels and maintenance dosages, but no correlation was observed between blood levels and RR. Any significant difference was not identified in TPM levels between the effective group (RR ≥50%) and the ineffective group (RR <50%; P = 0.159). In the subgroup of patients who did not use valproic acid, a significant difference in TPM levels was apparent between the effective and ineffective groups (P = 0.029). The optimal range of TPM was advocated 3.5-5.0 μg/mL. The optimal range was set, so that ranges did not overlap between the effective and ineffective groups. No patients experienced any side effects.

CONCLUSIONS

Measuring blood levels of TPM based on the classification of concomitant drugs and adjusting the dosage to reach the optimal range were recommended.

Pharmacokinetic considerations for anti-epileptic drugs in children

INTRODUCTION

Epilepsy is a chronic and debilitating neurological disease, with a peak of incidence in the first years of life. Today, the vast armamentarium of antiepileptic drugs (AEDs) available make even more challenging to select the most appropriate AED and establish the most effective dosing regimen. In fact, AEDs pharmacokinetics is under the influence of important age-related factors which cannot be ignored. Areas covered: Physiological changes occurring during development age (different body composition, immature metabolic patterns, reduced renal activity) can significantly modify the pharmacokinetic profile of AEDs (adsorption, volume of distribution, half-life, clearance), leading to an altered treatment response. We reviewed the main pharmacokinetic characteristics of AEDs used in children, focusing on age-related factors which are of relevance when treating this patient population. Expert opinion: To deal with this pharmacokinetic variability, physicians have at their disposal two tools: 1) therapeutic drug concentration monitoring, which may help to set the optimal therapeutic regimen for each patient and to monitor eventual fluctuation, and 2) the use of extended-release drug formulations, when available. In the next future, the development of 'ad-hoc' electronic dashboard systems will represent relevant decision-support tools making the AED therapy even more individualized and precise, especially in children.

Pharmacokinetics and Drug Interaction of Antiepileptic Drugs in Children and Adolescents

Selecting the most appropriate antiepileptic drug (AED) or combination of drugs for each patient and identifying the most suitable therapeutic regimen for their needs is increasingly challenging, especially among pediatric populations. In fact, the pharmacokinetics of several drugs vary widely in children with epilepsy because of age-related factors, which can influence the absorption, distribution, metabolism, and elimination of the pharmacological agent. In addition, individual factors, such as seizure type, associated comorbidities, individual pharmacokinetics, and potential drug interactions, may contribute to large fluctuations in serum drug concentrations and, therefore, clinical response. Therapeutic drug concentration monitoring (TDM) is an essential tool to deal with this complexity, enabling the definition of individual therapeutic concentrations and adaptive control of dosing to minimize drug interactions and prevent loss of efficacy or toxicity. Moreover, pharmacokinetic/pharmacodynamic modelling integrated with dashboard systems have recently been tested in antiepileptic therapy, although more clinical trials are required to support their use in clinical practice. We review the mechanism of action, pharmacokinetics, drug-drug interactions, and safety/tolerability profiles of the main AEDs currently used in children and adolescents, paying particular regard to issues of relevance when treating this patient population. Indications for TDM are provided for each AED as useful support to the clinical management of pediatric patients with epilepsy by optimizing pharmacological therapy.

Pyridoxine Add-On Treatment for the Control of Behavioral Adverse Effects Induced by Levetiracetam in Children: A Case-Control Prospective Study

BACKGROUND

Few studies on adult and pediatric patients have shown pyridoxine efficacy as additional therapy for those receiving levetiracetam (LEV) to prevent and mitigate behavioral adverse effects (BAEs).

OBJECTIVE

The aim of our study was to analyze the safety and efficacy of pyridoxine supplementation in the prevention of LEV adverse effects, including suicidal ideation.

METHODS

This randomized, case-control trial included patients receiving LEV as monotherapy treatment. Patients were subdivided into 2 groups, according to whether they were treated with LEV only (group 1) or LEV with supplemental pyridoxine (group 2).

RESULTS

In both cohorts, the most frequent BAEs were irritability/aggression followed by depression and confusion. Those patients (92%) who initiated pyridoxine after 1 month of LEV treatment did not need to change or suspend LEV ( P < 0.001), and BAE improved after 9.06 ± 3.05 days of pyridoxine supplementation. None of the patients complained of symptoms of pyridoxine toxicity, and no new adverse effects of LEV off-label were reported.

CONCLUSIONS

In our study, we found pyridoxine to be safe and effective in controlling LEV-induced BAEs in children.

An Updated Overview on Therapeutic Drug Monitoring of Recent Antiepileptic Drugs

Given the distinctive characteristics of both epilepsy and antiepileptic drugs (AEDs), therapeutic drug monitoring (TDM) can make a significant contribution to the field of epilepsy. The measurement and interpretation of serum drug concentrations can be of benefit in the treatment of uncontrollable seizures and in cases of clinical toxicity; it can aid in the individualization of therapy and in adjusting for variable or nonlinear pharmacokinetics; and can be useful in special populations such as pregnancy. This review examines the potential for TDM of newer AEDs such as eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, perampanel, pregabalin, rufinamide, retigabine, stiripentol, tiagabine, topiramate, vigabatrin, and zonisamide. We describe the relationships between serum drug concentration, clinical effect, and adverse drug reactions for each AED as well as the different analytical methods used for serum drug quantification. We discuss retrospective studies and prospective data on the serum drug concentration-efficacy of these drugs and present the pharmacokinetic parameters, oral bioavailability, reference concentration range, and active metabolites of newer AEDs. Limited data are available for recent AEDs, and we discuss the connection between drug concentrations in terms of clinical efficacy and nonresponse. Although we do not propose routine TDM, serum drug measurement can play a beneficial role in patient management and treatment individualization. Standardized studies designed to assess, in particular, concentration-efficacy-toxicity relationships for recent AEDs are urgently required.

Effect of CYP Inducers/Inhibitors on Topiramate Concentration: Clinical Value of Therapeutic Drug Monitoring

BACKGROUND

This study investigated the pharmacokinetic interactions between topiramate (TPM) and concomitant antiepileptic drugs and evaluated the therapeutic concentration range of TPM and the effect of the achieved plasma concentration on the retention rate of TPM therapy.

METHODS

A total of 1217 plasma samples obtained from 610 patients were retrospectively investigated, and the concentration-to-dose ratio (CD ratio) of TPM was compared among patients on various antiepileptic drug regimens. In addition, the therapeutic concentration of TPM was reviewed in patients on long-term therapy, and factors influencing the retention rate of TPM were analyzed by the Kaplan-Meier method.

RESULTS

Among patients using hepatic enzyme inducers (phenytoin, phenobarbital, and carbamazepine), the CD ratio was reduced by 45.4% in adults and 33.3% in children. Patients taking phenytoin concomitantly had a significantly lower CD ratio than patients taking phenobarbital or carbamazepine. Among noninducers, concomitant use of stiripentol increased the CD ratio. In 276 patients who remained on TPM therapy for more than 2 years, the mean therapeutic concentration was 5.1 mcg/mL (15.0 μmol/L). The estimated retention day was significantly higher for patients with a TPM concentration >5 mcg/mL than that for patients with a concentration <5 mcg/mL (945 versus 802 days; P = 0.007 by the log-rank test). Also, patients without hepatic enzyme inducers had a significantly higher retention rate than patients using such inducers (P = 0.002).

CONCLUSIONS

Concomitant use of hepatic enzyme inducers markedly reduced the plasma TPM concentration and can decrease its antiepileptic effect. A therapeutic concentration of >5 mcg/mL TPM was significantly associated with continuation of therapy, and therapeutic drug monitoring can be helpful.

Pharmacokinetic interactions and dosing rationale for antiepileptic drugs in adults and children

AIMS

Population pharmacokinetic modelling has been widely used across many therapeutic areas to identify sources of variability, which are incorporated into models as covariate factors. Despite numerous publications on pharmacokinetic drug-drug interactions (DDIs) between antiepileptic drugs (AEDs), such data are not used to support the dose rationale for polytherapy in the treatment of epileptic seizures. Here we assess the impact of DDIs on plasma concentrations and evaluate the need for AED dose adjustment.

METHODS

Models describing the pharmacokinetics of carbamazepine, clobazam, clonazepam, lamotrigine, levetiracetam, oxcarbazepine, phenobarbital, phenytoin, topiramate, valproic acid and zonisamide in adult and paediatric patients were collected from the published literature and implemented in NONMEM v7.2. Taking current clinical practice into account, we explore simulation scenarios to characterize AED exposure in virtual patients receiving mono- and polytherapy. Steady-state, maximum and minimum concentrations were selected as parameters of interest for this analysis.

RESULTS

Our simulations show that DDIs can cause major changes in AED concentrations both in adults and children. When more than one AED is used, even larger changes are observed in the concentrations of the primary drug, leading to significant differences in steady-state concentration between mono- and polytherapy for most AEDs. These results suggest that currently recommended dosing algorithms and titration procedures do not ensure attainment of appropriate therapeutic concentrations.

CONCLUSIONS

The effect of DDIs on AED exposure cannot be overlooked. Clinical guidelines must consider such covariate effects and ensure appropriate dosing recommendations for adult and paediatric patients who require combination therapy.

Pharmacotherapy in pediatric epilepsy: from trial and error to rational drug and dose selection - a long way to go

INTRODUCTION

Whereas ongoing efforts in epilepsy research focus on the underlying disease processes, the lack of a physiologically based rationale for drug and dose selection contributes to inadequate treatment response in children. In fact, limited information on the interindividual variation in pharmacokinetics and pharmacodynamics of anti-epileptic drugs (AEDs) in children drive prescription practice, which relies primarily on dose regimens according to a mg/kg basis. Such practice has evolved despite advancements in pediatric pharmacology showing that growth and maturation processes do not correlate linearly with changes in body size.

AREAS COVERED

In this review we aim to provide 1) a comprehensive overview of the sources of variability in the response to AEDs, 2) insight into novel methodologies to characterise such variation and 3) recommendations for treatment personalisation.

EXPERT OPINION

The use of pharmacokinetic-pharmacodynamic principles in clinical practice is hindered by the lack of biomarkers and by practical constraints in the evaluation of polytherapy. The identification of biomarkers and their validation as tools for drug development and therapeutics will require some time. Meanwhile, one should not miss the opportunity to integrate the available pharmacokinetic data with modeling and simulation concepts to prevent further delays in the development of personalised treatments for pediatric patients.

On the Slow Diffusion of Point-of-Care Systems in Therapeutic Drug Monitoring

Recent advancements in point-of-care (PoC) technologies show great transformative promises for personalized preventative and predictive medicine. However, fields like therapeutic drug monitoring (TDM), that first allowed for personalized treatment of patients' disease, still lag behind in the widespread application of PoC devices for monitoring of patients. Surprisingly, very few applications in commonly monitored drugs, such as anti-epileptics, are paving the way for a PoC approach to patient therapy monitoring compared to other fields like intensive care cardiac markers monitoring, glycemic controls in diabetes, or bench-top hematological parameters analysis at the local drug store. Such delay in the development of portable fast clinically effective drug monitoring devices is in our opinion due more to an inertial drag on the pervasiveness of these new devices into the clinical field than a lack of technical capability. At the same time, some very promising technologies failed in the clinical practice for inadequate understanding of the outcome parameters necessary for a relevant technological breakthrough that has superior clinical performance. We hope, by over-viewing both TDM practice and its yet unmet needs and latest advancement in micro- and nanotechnology applications to PoC clinical devices, to help bridging the two communities, the one exploiting analytical technologies and the one mastering the most advanced techniques, into translating existing and forthcoming technologies in effective devices.

Advances in anti-epileptic drug testing

In the past twenty-one years, 17 new antiepileptic drugs have been approved for use in the United States and/or Europe. These drugs are clobazam, ezogabine (retigabine), eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, perampanel, pregabalin, rufinamide, stiripentol, tiagabine, topiramate, vigabatrin and zonisamide. Therapeutic drug monitoring is often used in the clinical dosing of the newer anti-epileptic drugs. The drugs with the best justifications for drug monitoring are lamotrigine, levetiracetam, oxcarbazepine, stiripentol, and zonisamide. Perampanel, stiripentol and tiagabine are strongly bound to serum proteins and are candidates for monitoring of the free drug fractions. Alternative specimens for therapeutic drug monitoring are saliva and dried blood spots. Therapeutic drug monitoring of the new antiepileptic drugs is discussed here for managing patients with epilepsy.

Clinical pharmacokinetics of new-generation antiepileptic drugs at the extremes of age: an update

Epilepsies occur across the entire age range, and their incidence peaks in the first years of life and in the elderly. Therefore, antiepileptic drugs (AEDs) are commonly used at the extremes of age. Rational prescribing in these age groups requires not only an understanding of the drugs' pharmacodynamic properties, but also careful consideration of potential age-related changes in their pharmacokinetic profile. The present article, which updates a review published in 2006 in this journal, focuses on recent findings on the pharmacokinetics of new-generation AEDs in neonates, infants, children, and the elderly. Significant new information on the pharmacokinetics of new AEDs in the perinatal period has been acquired, particularly for lamotrigine and levetiracetam. As a result of slow maturation of the enzymes involved in glucuronide conjugation, lamotrigine elimination occurs at a particularly slow rate in neonates, and becomes gradually more efficient during the first months of life. In the case of levetiracetam, elimination occurs primarily by renal excretion and is also slow at birth, but drug clearance increases rapidly thereafter and can even double within 1 week. In general, infants older than 2-3 months and children show higher drug clearance (normalized for body weight) than adults. This pattern was confirmed in recent studies that investigated the pediatric pharmacokinetics of several new AEDs, including levetiracetam, rufinamide, stiripentol, and eslicarbazepine acetate. At the other extreme of age, in the elderly, drug clearance is generally reduced compared with younger adults because of less efficient drug-metabolizing activity, decreased renal function, or both. This general pattern, described previously for several AEDs, was confirmed in recent studies on the effect of old age on the clearance of felbamate, levetiracetam, pregabalin, lacosamide, and retigabine. For those drugs which are predominantly eliminated by renal excretion, aging-related pharmacokinetic changes could be predicted by measuring creatinine clearance (CLCR). Overall, most recent findings confirm that age is a major factor influencing the pharmacokinetic profile of AEDs. However, pharmacokinetic variability at any age can be considerable, and the importance of other factors should not be disregarded. These include genetic factors, co-morbidities, and drug interactions, particularly those caused by concomitantly administered AEDs which induce or inhibit drug-metabolizing enzymes.

Therapeutic drug monitoring of antiepileptic drugs by use of saliva

Blood (serum/plasma) antiepileptic drug (AED) therapeutic drug monitoring (TDM) has proven to be an invaluable surrogate marker for individualizing and optimizing the drug management of patients with epilepsy. Since 1989, there has been an exponential increase in AEDs with 23 currently licensed for clinical use, and recently, there has been renewed and extensive interest in the use of saliva as an alternative matrix for AED TDM. The advantages of saliva include the fact that for many AEDs it reflects the free (pharmacologically active) concentration in serum; it is readily sampled, can be sampled repetitively, and sampling is noninvasive; does not require the expertise of a phlebotomist; and is preferred by many patients, particularly children and the elderly. For each AED, this review summarizes the key pharmacokinetic characteristics relevant to the practice of TDM, discusses the use of other biological matrices with particular emphasis on saliva and the evidence that saliva concentration reflects those in serum. Also discussed are the indications for salivary AED TDM, the key factors to consider when saliva sampling is to be undertaken, and finally, a practical protocol is described so as to enable AED TDM to be applied optimally and effectively in the clinical setting. Overall, there is compelling evidence that salivary TDM can be usefully applied so as to optimize the treatment of epilepsy with carbamazepine, clobazam, ethosuximide, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, phenobarbital, phenytoin, primidone, topiramate, and zonisamide. Salivary TDM of valproic acid is probably not helpful, whereas for clonazepam, eslicarbazepine acetate, felbamate, pregabalin, retigabine, rufinamide, stiripentol, tiagabine, and vigabatrin, the data are sparse or nonexistent.

The efficacy and safety of newer anticonvulsants in patients with dementia

Anticonvulsants are a class of medications that have received considerable interest as possible treatments in patients with behavioural disturbances in dementia. The role of these medications for such a use remains controversial. The current paper reviews the published evidence surrounding the safety and efficacy (i.e. as a behavioural and cognitive treatment) of newer anticonvulsants in patients with dementia. A MEDLINE, International Pharmaceutical Abstracts, PsycINFO and clinicaltrials.gov search through to December 2011 was conducted for anticonvulsants that have received regulatory approval since 1996. Studies reporting behavioural or cognitive outcomes in patients with dementia were included. Nine trials involving only four medications met selection criteria and were included: levetiracetam (n = 4), oxcarbazepine (n = 1), topiramate (n = 2) and zonisamide (n = 2). Levetiracetam may have a role in the treatment of behavioural symptoms in dementia but study limitations substantially hinder the strength of such a recommendation. Oxcarbazepine and topiramate, based on limited data, do not appear to be effective treatments of behavioural symptoms in dementia. A lack of trials do not allow for conclusions to be made regarding zonisamide. From a cognitive standpoint, levetiracetam was the anticonvulsant most examined in patients with dementia, it appears to have less deleterious effects than some anticonvulsants. Limited data are available on the safety of these medications in elderly patients; however, studies completed thus far have demonstrated some adverse events that are more common or problematic with the use of these drugs in this patient population (i.e. somnolence, dizziness, hyponatraemia, weight loss).

A systematic review of the pharmacokinetics of antiepileptic drugs in neonates with refractory seizures

BACKGROUND

Neonatal seizures are associated with neurological sequelae and an increased risk of epilepsy later in life. Phenobarbital and phenytoin remain the antiepileptic drugs (AEDs) most commonly used to treat neonatal seizures, despite their suboptimal effectiveness and safety. As a result, other AEDs, such as levetiracetam and topiramate, are often used in neonates with refractory seizures, despite limited data and off-label use.

OBJECTIVES

To systematically review published pharmacokinetic data for second-line AEDs used in neonates with seizures and to provide dosing recommendations for these agents in the neonatal population.

METHODS

A literature search was conducted in PubMed (1949-May 2012), Medline (1950-May 2012), and Embase (1980-May 2012). Each study was ranked according to the quality of evidence it provided, based on the classification system developed by the US Preventive Services Task Force. Information extracted from each study included study design, number of subjects, gestational and postnatal age, AED dosage regimen, pharmacokinetic parameters, pharmacokinetic model, AED serum concentrations, and sampling times.

RESULTS

Nineteen relevant pharmacokinetic studies involving a total of 8 different drugs were identified. No prospective, randomized, controlled studies (level I evidence) or nonrandomized controlled studies (level II-I evidence) were identified; 2 studies were prospective, nonrandomized, uncontrolled (cohort) studies (level II-2 evidence), 11 studies obtained evidence from multiple time series (level II-3 evidence), and 6 studies were case reports or descriptive studies (level III evidence).

CONCLUSIONS

There are limited pharmacokinetic data for the use of carbamazepine, levetiracetam, lidocaine, paraldehyde, topiramate, valproic acid, and vigabatrin for neonates with seizures refractory to treatment with first-line antiepileptic agents. Further research is needed to elucidate target AED serum concentrations (if any) required to optimize effectiveness and minimize dose-related adverse effects in neonates.

Levetiracetam versus carbamazepine in patients with late poststroke seizures: a multicenter prospective randomized open-label study (EpIC Project)

BACKGROUND

Strokes are the leading cause of epileptic seizures in adults and account for 50% of seizures in those over the age of 65 years. The use of antiepileptic drugs to prevent recurrent poststroke seizures is recommended.

METHODS

One hundred and twenty-eight patients with poststroke seizures were randomly allocated to treatment with either levetiracetam (LEV) or sustained-release carbamazepine (CBZ) in a multicenter randomized open-label study. After a titration study phase (2 weeks), the optimal individual dose of trial medication was determined and treatment was continued for another 52 weeks. The primary endpoint was defined as the proportion of seizure-free patients; the secondary endpoints were: evaluation of time recurrence to the first seizure, EEG tracings, cognitive functions and side effects.

RESULTS

Of 128 patients, 22 discontinued the trial prematurely; thus a total of 106 patients (52 treated with LEV and 54 treated with CBZ) were included in the analysis. The results of the study were as follows: no significant difference in number of seizure-free patients between LEV and CBZ (p = 0.08); time to the first recurrence tended to be longer among patients on LEV; there was no correlation between the therapeutic effect and the EEG findings in either treatment group; LEV caused significantly fewer (p = 0.02) side effects than CBZ; attention deficit, frontal executive functions and functional scales (Activities of Daily Living and Instrumental Activities of Daily Living indices) were significantly worse in the CBZ group.

CONCLUSIONS

This trial suggests that LEV may be a valid alternative to CBZ in poststroke seizures, particularly in terms of efficacy and safety. In addition, our results show that LEV has significant advantages over CBZ on cognitive functions. This trial also indicates that LEV in monotherapy is a safe and effective therapeutic option in elderly patients who have suffered epileptic seizures following a stroke.

Utilization patterns of antiepileptic drugs among adult epileptic patients at a tertiary hospital in Oman

Objectives

To describe utilization patterns of antiepileptic drugs (AEDs) among adult epileptic patients at a tertiary hospital in Oman.

Methods

Data were collected retrospectively from January 2006 to December 2009. The study included all adult (&gt;18 years) epileptic patients on AEDs and followed up at a neurology clinic at Sultan Qaboos University Hospital in Oman. All reported therapeutic drug monitoring (TDM) requests for serum AED concentrations were also collected. Institutional ethical approval was sought and obtained.

Key findings

The study included a total of 372 patients with a mean age of 34 ± 15 years. Monotherapy AEDs accounted for 53% of the prescriptions, whereas polytherapy with two or three AED combinations accounted for 27% and 20% respectively. The most frequently prescribed AED was sodium valproate (27%) followed by carbamazepine (23%). The commonly prescribed AED combinations were sodium valproate with clonazepam (12%) followed by sodium valproate with lamotrigine (12%). Evaluation of 574 TDM requests for three AEDs showed that 57% of carbamazepine, 78% of phenytoin and 54% of valproic acid requests were either above or below the recommended therapeutic threshold. Most of these requests were ordered from the hospital's emergency department for suspected insufficient serum concentrations.

Conclusions

Antiepileptic drug monotherapy is still the most frequently employed therapeutic strategy in adult patients with epilepsy in keeping with the standard therapeutic guidelines. Sodium valproate is commonly used for different types of seizures reflecting its wide spectrum of anticonvulsant potential. Newer AED utilizations are becoming increasingly popular in our subjects particularly as add-on with other standard AEDs.

Practices Associated with Serum Antiepileptic Drug Level Monitoring at a Pediatric Neurology Clinic

Objectives: To assess the practices associated with the application of therapeutic drug monitoring (TDM) for antiepileptic drugs (AEDs) in the management of children with structural–metabolic epilepsy. Methods: It was a retrospective chart review and included children aged ≥2 years old with structural–metabolic epilepsy, treated with AEDs, and received TDM. The data were extracted from the medical records. Results: Thirty-two patients were identified with 50 TDM assays. In two thirds of the assays, “check level” and “recheck level” were the reasons behind the requesting of serum level monitoring of AEDs. Knowledge of serum AED levels led to alterations in the management in 60% of the assays. Thirty-two (76%) pediatrician’s actions were consistent with the recommendation of TDM pharmacist. Forty-nine (98%) levels were appropriately indicated. In relation to the appropriateness of sampling time, 9 (18%) levels were not assessed due to missing data. Twenty-seven (54%) levels were appropriately sampled. Conclusions: More studies should be designed to improve the component of the current TDM request form, especially in the reason section. By the same token, the number of pointless assays and the costs to the health care system can be reduced both by enhancing and improving the educational standards of the requesting neurologists

Host factors affecting antiepileptic drug delivery-pharmacokinetic variability

Antiepileptic drugs (AEDs) are the mainstay in the treatment of epilepsy, one of the most common serious chronic neurological disorders. AEDs display extensive pharmacological variability between and within patients, and a major determinant of differences in response to treatment is pharmacokinetic variability. Host factors affecting AED delivery may be defined as the pharmacokinetic characteristics that determine the AED delivery to the site of action, the epileptic focus. Individual differences may occur in absorption, distribution, metabolism and excretion. These differences can be determined by genetic factors including gender and ethnicity, but the pharmacokinetics of AEDs can also be affected by age, specific physiological states in life, such as pregnancy, or pathological conditions including hepatic and renal insufficiency. Pharmacokinetic interactions with other drugs are another important source of variability in response to AEDs. Pharmacokinetic characteristics of the presently available AEDs are discussed in this review as well as their clinical implications.

Specific safety and tolerability considerations in the use of anticonvulsant medications in children

Epilepsy is one of the most common neurological disorders in the pediatric age range, and the majority of affected children can be safely and effectively treated with antiepileptic medication. While there are many antiepileptic agents on the market, specific drugs may be more efficacious for certain seizure types or electroclinical syndromes. Furthermore, certain adverse effects are more common with specific classes of medication. Additionally patient-specific factors, such as age, race, other medical conditions, or concurrent medication use may result in higher rates of side effects or altered efficacy. Significant developmental changes in gastric absorption, protein binding, hepatic metabolism, and renal clearance are seen over the pediatric age range, which impact pharmacokinetics. Such changes must be considered to determine optimal dosing and dosing intervals for children at specific ages. Furthermore, approximately one third of children require polytherapy for seizure control, and many more take concurrent medications for other conditions. In such children, drug–drug interactions must be considered to minimize adverse effects and improve efficacy. This review will address issues of antiepileptic drug efficacy, tolerability and ease of use, pharmacokinetics, and drug–drug interactions in the pediatric age range.

Perinatal pharmacology: applications for neonatal neurology

The principles of clinical pharmacology also apply to neonates, but their characteristics warrant a tailored approach. We focus on aspects of both developmental pharmacokinetics (concentration/time relationship) and developmental pharmacodynamics (concentration/effect relationship) in neonates. We hereby aimed to link concepts used in clinical pharmacology with compound-specific observations (anti-epileptics, analgosedatives) in the field of neonatal neurology. Although in part anecdotal, we subsequently illustrate the relevance of developmental pharmacology in the field of neonatal neurology by a specific intervention (e.g. whole body cooling), specific clinical presentations (e.g. short and long term outcome following fetal exposure to antidepressive agents, the development of new biomarkers for fetal alcohol syndrome) and specific clinical needs (e.g. analgosedation in neonates, excitocytosis versus neuro-apoptosis/impaired synaptogenesis).

Anti-epileptic drugs

Therapeutic Reviews aim to provide essential independent information for health professionals about drugs used in palliative and hospice care. Additional content is available on www.palliativedrugs.com. Country-specific books (Hospice and Palliative Care Formulary USA, and Palliative Care Formulary, British and Canadian editions) are also available and can be ordered from www.palliativedrugs.com. The series editors welcome feedback on the articles (hq@palliativedrugs.com).

The effect of age and comedication on lamotrigine clearance, tolerability, and efficacy

PURPOSE

To compare pharmacokinetics, tolerability, and efficacy of lamotrigine (LTG) in older versus younger adults.

METHODS

We studied 686 adult outpatients seen at our center over 5 years. We compared apparent clearance (CL) of LTG in the youngest (16-36 years; n = 247) and oldest (55-92 years; n = 155) tertiles. We analyzed one-year retention for younger and older adults newly started on LTG, frequency of adverse effects causing intolerability, and rates of specific adverse effects. We also investigated 6-month seizure freedom.

KEY FINDINGS

Median LTG CL of older adults taking LTG in monotherapy was approximately 22% lower compared to younger adults (28.8 vs. 36.5 ml/h/kg; p < 0.001). LTG CL in older adults was lower compared to younger adults in patients on polytherapy and on polytherapy without enzyme inducers or valproate. One-year retention for LTG was comparable in older (78.1%, 121/155) and younger (72.4%, 179/247) adults. Intolerability to LTG was higher in older (34.8%) versus younger adults (24.2%; p = 0.005). Imbalance, drowsiness, and dizziness were common intolerable side effects in both groups. Older patients had higher rates of intolerability due to imbalance (16% vs. 4%), drowsiness (13% vs. 7%), and tremor (5% vs. 2%) compared with younger patients. Rates of 6-month seizure freedom were comparable, and small numbers of each group benefited from very high levels of LTG (>15 μg/ml).

SIGNIFICANCE

LTG CL in monotherapy in older adults is approximately 20% lower than in younger adults. For a given serum LTG level, older adults are twice as likely to have significant adverse effects compared to younger adults. Older patients are more likely to experience imbalance, drowsiness, and tremor than younger patients. Younger adults tolerate LTG better than older adults, but one-year retention is comparable. Some patients may benefit from high serum levels of LTG.

Topiramate pharmacokinetics in infants and young children: contribution of population analysis

PURPOSE

To determine the range of topiramate (TPM) concentrations obtained in children under 4 with the recommended dosage regimen (3-9 mg/kg/day) and to compare them to adult target ranges.

METHODS

The population pharmacokinetic model developed for TPM, with/without enzyme inducer antiepileptic drugs (EIAEDs) in children was used to determine dosage regimens providing AUC and trough concentrations (C(trough)s) within the adult ranges.

RESULTS

TPM pharmacokinetics was described by a one-compartment model. EIAEDs increased the apparent clearance (CL/F) and age and body weight increased the apparent distribution volume (Vd/F). Mean population estimates (% CV interindividual variability) were 0.608/1.15 L/h (13%) for CL/F without/with EIAEDs, 28.6L (0.2%) for Vd/F and 1.4h(-1) (124%) for the absorption rate constant. Mean AUC(0-12h) reached with a 2mg/kg/day dosing regimen was within described range. A 6-16 mg/kg/day dose depending on age allowed reaching target C(trough) range with the highest probability. Combined EIAEDs led to a 2- and 3-fold decrease in AUC and C(trough), respectively.

CONCLUSION

TPM dosage of 2/4 mg/kg/day (without/with EIEADs, respectively) provides the AUC reported in adults. In children under 4, alternative dosing regimen should be considered mainly when associated to EIAED to reach C(trough) comparable to adult values.

New drugs for pediatric epilepsy

The last 2 decades have witnessed an unprecedented period of new antiepileptic drug (AED) development. Newer-generation AEDs have been developed with the intention of improving the ease of use, decreasing drug interactions, decreasing adverse side effects, and identifying drugs with unique mechanisms of action, some of which may bear relevance to potential neuroprotective activity. Drug trials have also been refined in some cases to evaluate AED efficacy in children and against distinct epilepsy syndromes. This progress provides many new treatment options for the child neurologist facing children with epilepsy but also introduces the burden of determining appropriate AED choices. Here we highlight 6 new antiepileptic medications recently approved or pending approval for use in the United States: lacosamide, rufinamide, vigabatrin, retigabine, brivaracetam, and clobazam. For each of these medications, we present information regarding the history of drug development, proposed mechanism(s) of action, pharmacokinetics and recommended dosing, evidence for clinical efficacy, tolerability, and when, available, any unique features that are relevant for the pediatric population.

Developmental pharmacokinetics

Physiological differences between children and adults result in age-related differences in pharmacokinetics and drug effect. In neonates and infants, decreased weight-adjusted doses are required because of decreased protein binding, renal excretion, and/or metabolism. For children older than 1 year of age, significantly higher weight-corrected doses compared with adults are needed for drugs eliminated by the cytochrome P450 (CYP) isozymes CYP1A2, CYP2C9, and CYP3A4. In contrast, weight-corrected doses for drugs eliminated by renal excretion or metabolism by CYP2C19, CYP2D6, N-Acetyl-transferase, and UDP glucuronosyltransferase in children are similar to those in adults. Ideally, pharmacokinetic and pharmacodynamic data should be available for all drugs used in children. Because many drugs are not approved for pediatric use, data are often limited, especially for older drugs. Understanding the effects of age on pharmacokinetics can help to determine appropriate pediatric dosing in situations in which there is limited information.

Age and comedications influence levetiracetam pharmacokinetics in children

The pharmacokinetics of many antiepileptic drugs differs between adults and children. The influence of age and concomitant medications on the dose/concentration ratio of levetiracetam was examined in 103 children with epilepsy. Dosing and plasma levels of levetiracetam and concomitant antiepileptic drugs were reviewed retrospectively. The dose/concentration ratio was calculated as the weight-normalized dose (mg/kg/day) divided by the steady-state trough plasma drug level, which was used as a measure of apparent oral clearance of levetiracetam. Children were classified into age groups and treatment groups: levetiracetam given with enzyme inducers (n = 24) or nonenzyme inducers (n = 69), or as monotherapy (n = 10). Levetiracetam clearance differed significantly between age groups (0-4, 5-11, and 12-17 years), i.e., the younger the child, the higher the clearance. The increase was 1.7-fold between the youngest and oldest age groups. Children on enzyme inducers exhibited significantly higher clearance (1.3-fold), compared with those on nonenzyme inducers and monotherapy. Levetiracetam did not influence the clearance of lamotrigine, valproate, topiramate, or clonazepam. In conclusion, younger age and comedication with an enzyme inducer increased levetiracetam clearance. This finding should be taken into account when treating individual patients.