Clinical pharmacokinetics of antiepileptic drugs in paediatric patients. Part II. Phenytoin, carbamazepine, sulthiame, lamotrigine, vigabatrin, oxcarbazepine and felbamate

Pharmacokinetic considerations surrounding the use of levetiracetam for seizure prophylaxis in neurocritical care - an overview

INTRODUCTION

Levetiracetam (LEV) is one of the most widely used anti-seizure medications (ASMs) in clinical practice. This is due both to a different mechanism of action when compared to other ASMs and its easy handling. Indeed, because of its interesting pharmacokinetic properties, it is often used outside of the labeled indications, notably in the neurocritical setting as prophylaxis of epileptic seizures.

AREAS COVERED

A literature search was conducted and the most relevant studies on the pharmacokinetic properties of LEV were selected by two independent investigators. Current evidence on the use of ASM prophylaxis in the neurocritical setting was also reviewed, highlighting and discussing the strengths and limits of LEV as drug of choice for anti-epileptic prophylaxis in this scenario.

EXPERT OPINION

LEV has a 'near-ideal' pharmacokinetic profile, which makes it an attractive drug for ASM prophylaxis in neurocritical care. However, current recommendations restrict ASMs prophylaxis to very selected circumstances and the role of LEV is marginal. Moreover, studies are generally designed to compare LEV versus phenytoin, whereas studies comparing LEV versus placebo are lacking. Further, randomized trials will be needed to better elucidate LEV utility and its neuroprotective role in the neurocritical setting.

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.

Simultaneous Determination of Lamotrigine, Topiramate, Oxcarbazepine, and 10,11-dihydro-10-hydroxycarbazepine in Human Blood Plasma by UHPLC-MS/MS

Background:

Lamotrigine (LTG), topiramate (TPM), and oxcarbazepine (OXC) are commonly used antiepileptic drugs. The bioactivity and toxicity of these drugs were related to their blood concentrations which varied greatly among individuals and required to be monitored for dose adjustment. However, the commercial method for monitoring of these drugs is not available in China.

Methods:

A UHPLC-MS/MS method for simultaneous determination of LTG, TPM, OXC, and OXC active metabolite (10,11-dihydro-10-hydroxycarbazepine, MHD) was developed and validated according to the guidelines and applied in clinical practice.

Results:

he separation was achieved by using methanol and water (both contain 0.1% formic acid) at 0.4 mL/min under gradient elution within 3 min. For all analytes, the isotope internal standard was used; the selectivity was good without significant carry over; LTG and TPM were linear between 0.06 to 12 mg/L while OXC and MHD were linear between 0.03 to 6 mg/L, the upper limit could be 10-fold higher because 10-fold dilution with water did not affect the results; the intra-day and interday bias and imprecision were -13.11% to 5.42% and < 13.32%; the internal standard normalized recovery and matrix factor were 90.95% to 111.94% and 95.57% to 109.91%; and all analytes were stable under tested conditions. LTG and OXC-D4 shared two ion pairs m/z 257.1 > 212.0 and 257.1 > 184.0, and m/z 257.1 > 240.0 was suggested for OXC-D4 quantitation. Lamotrigine and lamotrigine- 13C3 shared three ion pairs m/z 259.0 > 214.0, 259.0 > 168.0 and 259.0 > 159.0, and m/z 259.0 > 144.9 was suggested for LTG-13C3 quantitation. CBZ had a slight influence on OXC analysis only at 0.225 mg/L (bias, 20.24%) but did not affect MHD analysis. Optimization of chromatography conditions was useful to avoid the influence of isobaric mass transitions on analysis. This method has been successfully applied in 208 patients with epilepsy for dose adjustment.

Conclusions:

An accurate, robust, rapid, and simple method for simultaneous determination of LTG, TPM, OXC, and MHD by UHPLC-MS/MS was developed, validated, and successfully applied in patients with epilepsy for dose adjustment. The experiences during method development, validation, and application might be helpful for other researchers.

Sultiame pharmacokinetic profile in plasma and erythrocytes after single oral doses: A pilot study in healthy volunteers

A pilot study was conducted aiming at specifying sultiame's pharmacokinetic profile, completed by in vitro assays evaluating the intraerythrocytic transfer of sultiame and by a pharmacokinetic model assessing its distribution. Single oral doses of sultiame (Ospolot^® 50, 100, and 200 mg) were administered in open‐label to four healthy volunteers. Serial plasma, whole blood, and urine samples were collected. A spiking experiment was also performed to characterize sultiame's exchanges between plasma and erythrocytes in vitro. Pharmacokinetic parameters were evaluated using standard noncompartmental calculations and nonlinear mixed‐effect modeling. The plasma maximal concentrations (C_max) showed striking nonlinear disposition of sultiame, with a 10‐fold increase while doses were doubled. Conversely, whole blood C_max increased less than dose proportionally while staying much higher than in plasma. Quick uptake of sultiame into erythrocytes observed in vivo was confirmed in vitro, with minimal efflux. A two‐compartment model with first‐order absorption, incorporating a saturable ligand to receptor binding, described the data remarkably well, indicating apparent plasma clearance of 10.0 L/h (BSV: 29%) and distribution volume of 64.8 L; saturable uptake into an intracellular compartment of 3.3 L with a maximum binding capacity of 111 mg accounted for nonlinearities observed in plasma and whole blood concentrations. Pharmacokinetic characteristics of sultiame are reported, including estimates of clearance and volume of distribution that were so far unpublished. The noticeable nonlinearity in sultiame disposition should be taken into account for the design of future studies and the interpretation of therapeutic drug monitoring results.

Efficacy of antiepileptic drugs in neonatal seizures: a systematic review protocol

INTRODUCTION

Seizures are one of the most common neurological disorders of neonates, which is also an emergency in the neonatal intensive care unit. For neonates, the recommended first-line antiepileptic drugs (AEDs) include phenobarbitone, which may be effective in only 50% of seizures. Some new AEDs, such as levetiracetam, have been shown to be effective in adults and older children. However, their efficacy for neonatal seizures remains uncertain. The aim of this investigation is to conduct a systematic review to evaluate the efficacy of all AEDs in neonates. Additionally, the long-term outcomes following neonatal seizures, in relation to the development of cerebral palsy and epilepsy, will be studied.

METHOD

We will perform a systematic review including randomised controlled studies (RCTs), cohort studies, case-controlled studies and case series studies which evaluated the efficacy of AEDs and short-term and long-term outcomes in neonatal seizures. PubMed, Embase, Web of Science, Cochrane Library and Clinical trial.gov will be searched. There will be no language restriction. Risk bias in RCTs will be evaluated by the Cochrane risk-of-bias tool, while cohort and case-control studies will be evaluated by the Newcastle-Ottawa Scale. A network meta-analysis will be performed by the Bayesian model using WinBUGS V.1.4.3 and R software if there is a high degree of homogeneity among studies. Otherwise, we will perform a narrative review without pooling. Subgroup analyses will be performed in different AEDs and dosage groups.

OUTCOME

The primary outcomes will be seizure cessation confirmed by electroencephalogram and long-term neurodevelopmental outcome. Secondary outcomes will be neonatal mortality during hospitalisation and suspected drug toxicity.

ETHICS AND DISSEMINATION

Formal ethical approval is not required as no primary data are collected. This systematic review will be disseminated through a peer-reviewed publication.

Pharmacotherapy for Focal Seizures in Children and Adolescents

Focal-onset seizures are among the most common forms of seizures in children and adolescents and can be caused by a wide diversity of acquired or genetic etiologies. Despite the increasing array of antiseizure drugs available, treatment of focal-onset seizures in this population remains problematic, with as many as one-third of children having seizures refractory to medications. This review discusses contemporary concepts in focal seizure classification and pathophysiology and describes the antiseizure medications most commonly chosen for this age group. As antiseizure drug efficacy is comparable in children and adults, here we focus on pharmacokinetic aspects, drug-drug interactions, and side effect profiles. Finally, we provide some suggestions for choosing the optimal medication for the appropriate patient.

Pharmacokinetic considerations for anti-epileptic drugs in children

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.

Development of cortical motor circuits between childhood and adulthood: A navigated TMS-HdEEG study

Motor functions improve during childhood and adolescence, but little is still known about the development of cortical motor circuits during early life. To elucidate the neurophysiological hallmarks of motor cortex development, we investigated the differences in motor cortical excitability and connectivity between healthy children, adolescents, and adults by means of navigated suprathreshold motor cortex transcranial magnetic stimulation (TMS) combined with high-density electroencephalography (EEG). We demonstrated that with development, the excitability of the motor system increases, the TMS-evoked EEG waveform increases in complexity, the magnitude of induced activation decreases, and signal spreading increases. Furthermore, the phase of the oscillatory response to TMS becomes less consistent with age. These changes parallel an improvement in manual dexterity and may reflect developmental changes in functional connectivity. Hum Brain Mapp 38:2599-2615, 2017. © 2017 Wiley Periodicals, Inc.

Clinical Drug Development in Epilepsy Revisited: A Proposal for a New Paradigm Streamlined Using Extrapolation

Data from clinical trials in adults, extrapolated to predict benefits in paediatric patients, could result in fewer or smaller trials being required to obtain a new drug licence for paediatrics. This article outlines the place of such extrapolation in the development of drugs for use in paediatric epilepsies. Based on consensus expert opinion, a proposal is presented for a new paradigm for the clinical development of drugs for focal epilepsies. Phase I data should continue to be collected in adults, and phase II and III trials should simultaneously recruit adults and paediatric patients aged above 2 years. Drugs would be provisionally licensed for children subject to phase IV collection of neurodevelopmental safety data in this age group. A single programme of trials would suffice to license the drug for use as either adjunctive therapy or monotherapy. Patients, clinicians and sponsors would all benefit from this new structure through cost reduction and earlier access to novel treatments. Further work is needed to elicit the views of patients, their parents and guardians as appropriate, regulatory authorities and bodies such as the National Institute for Health and Care Excellence (UK).

Association between PK/PD-involved gene polymorphisms and carbamazepine-individualized therapy

Aim: To evaluate the association between the major genetic variants involved in the pharmacokinetic/pharmacodynamic (PK/PD) properties of carbamazepine (CBZ) and its maintenance doses and concentrations. Patients & methods: The genotypes of 166 patients receiving CBZ monotherapy were detected using high-resolution melting curve (HRM) and TaqMan methods. Results: Both univariate and multiple regression analyses revealed that carriers of the SCN1A IVS5–91G>A or EPHX1 c.337T>C allele tended to require a higher CBZ dose and a lower CBZ natural logarithmic concentration–dose ratio (lnCDR) than noncarriers (p < 0.05). Furthermore, two interactions between these genes were associated with the lnCDR and the maintenance dosage of CBZ, respectively. Conclusion: SCN1A IVS5–91G>A gene polymorphism is potential genetic biomarker associated with the PK of CBZ.

Detection of Mild and Reversible Neurohistopathological Changes in the Brain of Juvenile (Preweaned) Beagle Dogs Treated with Vigabatrin for up to 91 Days

Neurohistopathological changes in the brain were assessed in juvenile beagle dogs given vigabatrin at 30 or 100 mg/kg/day by oral gavage from postnatal day 22 (PND22) until 16 weeks of age (PND112), when brain myelination is considered to reach the adult stage in dogs. Separate subgroups were treated from PND22 to PND35 or PND36 to PND49 to assess early effects. In addition to extensive brain histopathology, there were assessments of toxicokinetics, clinical condition, body weight, organ weights, and macroscopic pathology. In animals treated for 14 days from PND22, minimal or slight vacuolation was seen in the neuropil of the septal nuclei, hippocampus, hypothalamus, thalamus, cerebellum, and globus pallidus at 100 mg/kg/day and minimal vacuolation in the thalamus, globus pallidus, and cerebellum at 30 mg/kg/day. In animals given 100 mg/kg/day for 91 days from PND22, minimal or slight vacuolation was observed only in the hippocampus, hypothalamus, and thalamus. No vigabatrin-related brain vacuolation was observed in animals given 30 or 100 mg/kg/day for 14 days from PND36. Clear evidence of recovery was observed after 14-day and 6-week off-dose periods that followed treatment from PND22 to PND35 or PND22 to PND112, respectively.

Seizure occurrence and the circadian rhythm of cortisol: a systematic review

PURPOSE

Stress is the seizure precipitant most often reported by patients with epilepsy or their caregivers. The relation between stress and seizures is presumably mediated by stress hormones such as cortisol, affecting neuronal excitability. Endogenous cortisol is released in a circadian pattern. To gain insight into the relation between the circadian rhythm of cortisol and seizure occurrence, we systematically reviewed studies on the diurnal distribution of epileptic seizures in children and adults and linked the results to the circadian rhythm of cortisol.

METHODS

A structured literature search was conducted to identify relevant articles, combining the terms 'epilepsy' and 'circadian seizure distribution', plus synonyms. Articles were screened using predefined selection criteria. Data on 24-hour seizure occurrence were extracted, combined, and related to a standard circadian rhythm of cortisol.

RESULTS

Fifteen relevant articles were identified of which twelve could be used for data aggregation. Overall, seizure occurrence showed a sharp rise in the early morning, followed by a gradual decline, similar to cortisol rhythmicity. The occurrence of generalized seizures and focal seizures originating from the parietal lobe in particular followed the circadian rhythm of cortisol.

CONCLUSIONS

The diurnal occurrence of epileptic seizures shows similarities to the circadian rhythm of cortisol. These results support the hypothesis that circadian fluctuations in stress hormone level influence the occurrence of epileptic seizures.

Population pharmacokinetics of phenytoin in critically ill children

The objective was to study the population pharmacokinetics of bound and unbound phenytoin in critically ill children, including influences on the protein binding profile. A population pharmacokinetic approach was used to analyze paired protein-unbound and total phenytoin plasma concentrations (n = 146 each) from 32 critically ill children (0.08-17 years of age) who were admitted to a pediatric hospital, primarily intensive care unit. The pharmacokinetics of unbound and bound phenytoin and the influence of possible influential covariates were modeled and evaluated using visual predictive checks and bootstrapping. The pharmacokinetics of protein-unbound phenytoin was described satisfactorily by a 1-compartment model with first-order absorption in conjunction with a linear partition coefficient parameter to describe the binding of phenytoin to albumin. The partitioning coefficient describing protein binding and distribution to bound phenytoin was estimated to be 8.22. Nonlinear elimination of unbound phenytoin was not supported in this patient group. Weight, allometrically scaled for clearance and volume of distribution for the unbound and bound compartments, and albumin concentration significantly influenced the partition coefficient for protein binding of phenytoin. The population model can be applied to estimate the fraction of unbound phenytoin in critically ill children given an individual's albumin concentration.

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.

Sources of interindividual variability

The efficacy, safety, and tolerability of drugs are dependent on numerous factors that influence their disposition. A dose that is efficacious and safe for one individual may result in sub-therapeutic or toxic blood concentrations in other individuals. A major source of this variability in drug response is drug metabolism, where differences in pre-systemic and systemic biotransformation efficiency result in variable degrees of systemic exposure (e.g., AUC, C max, and/or C min) following administration of a fixed dose.Interindividual differences in drug biotransformation have been studied extensively. It is well recognized that both intrinsic (such as genetics, age, sex, and disease states) and extrinsic (such as diet, chemical exposures from the environment, and even sunlight) factors play a significant role. For the family of cytochrome P450 enzymes, the most critical of the drug metabolizing enzymes, genetic variation can result in the complete absence or enhanced expression of a functional enzyme. In addition, up- and down-regulation of gene expression, in response to an altered cellular environment, can achieve the same range of metabolic function (phenotype), but often in a less reliably predictable and time-dependent manner. Understanding the mechanistic basis for drug disposition and response variability is essential if we are to move beyond the era of empirical, trial-and-error dose selection and into an age of personalized medicine that brings with it true improvements in health outcomes in the therapeutic treatment of disease.

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.

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.

Pharmacotherapy of the third-generation AEDs: lacosamide, retigabine and eslicarbazepine acetate

INTRODUCTION

The search for new, more effective antiepileptic drugs (AEDs) continues. The three most recently approved drugs, the so-called third-generation AEDs, include lacosamide, retigabine and eslicarbazepine acetate and are licensed as adjunctive treatment of partial epilepsy in adults.

AREAS COVERED

For the above three AEDs, their mechanisms of action, pharmacokinetic characteristics, drug-drug interactions, pharmacotherapeutics, dose and administration and therapeutic drug monitoring are reviewed in this paper.

EXPERT OPINION

Lacosamide and retigabine act through novel mechanisms, while eslicarbazepine acetate, a pro-drug for eslicarbazepine, acts in a similar manner to several other AEDs. All three AEDs are associated with linear pharmacokinetic and rapid absorption and undergo metabolism. Their drug-drug interaction profile is low (lacosamide and retigabine) to modest (eslicarbazepine) in propensity. At the highest approved doses for the three AEDs, responder rates were similar. The most commonly observed adverse effects compared with placebo were dizziness, headache, diplopia and nausea for lacosamide; dizziness, somnolence and fatigue for retigabine and dizziness and somnolence for eslicarbazepine acetate. The precise role that these new AEDs will have in the treatment of epilepsy and whether they will make a significant impact on the prognosis of intractable epilepsy is not yet known and will have to await further clinical experience.

Improving the prediction of the brain disposition for orally administered drugs using BDDCS

In modeling blood-brain barrier (BBB) passage, in silico models have yielded ~80% prediction accuracy, and are currently used in early drug discovery. Being derived from molecular structural information only, these models do not take into account the biological factors responsible for the in vivo outcome. Passive permeability and P-glycoprotein (Pgp, ABCB1) efflux have been successfully recognized to impact xenobiotic extrusion from the brain, as Pgp is known to play a role in limiting the BBB penetration of oral drugs in humans. However, these two properties alone fail to explain the BBB penetration for a significant number of marketed central nervous system (CNS) agents. The Biopharmaceutics Drug Disposition Classification System (BDDCS) has proved useful in predicting drug disposition in the human body, particularly in the liver and intestine. Here we discuss the value of using BDDCS to improve BBB predictions of oral drugs. BDDCS class membership was integrated with in vitro Pgp efflux and in silico permeability data to create a simple 3-step classification tree that accurately predicted CNS disposition for more than 90% of 153 drugs in our data set. About 98% of BDDCS class 1 drugs were found to markedly distribute throughout the brain; this includes a number of BDDCS class 1 drugs shown to be Pgp substrates. This new perspective provides a further interpretation of how Pgp influences the sedative effects of H1-histamine receptor antagonists.

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.

Therapeutic Drug Monitoring of the Newer Anti-Epilepsy Medications

In the past twenty years, 14 new antiepileptic drugs have been approved for use in the United States and/or Europe. These drugs are eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, pregabalin, rufinamide, stiripentol, tiagabine, topiramate, vigabatrin and zonisamide. In general, the clinical utility of therapeutic drug monitoring has not been established in clinical trials for these new anticonvulsants, and clear guidelines for drug monitoring have yet to be defined. The antiepileptic drugs with the strongest justifications for drug monitoring are lamotrigine, oxcarbazepine, stiripentol, and zonisamide. Stiripentol and tiagabine are strongly protein bound and are candidates for free drug monitoring. Therapeutic drug monitoring has lower utility for gabapentin, pregabalin, and vigabatrin. Measurement of salivary drug concentrations has potential utility for therapeutic drug monitoring of lamotrigine, levetiracetam, and topiramate. Therapeutic drug monitoring of the new antiepileptic drugs will be discussed in managing patients with epilepsy.

Therapeutic Drug Monitoring of the Newer Anti-Epilepsy Medications

In the past twenty years, 14 new antiepileptic drugs have been approved for use in the United States and/or Europe. These drugs are eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, pregabalin, rufinamide, stiripentol, tiagabine, topiramate, vigabatrin and zonisamide. In general, the clinical utility of therapeutic drug monitoring has not been established in clinical trials for these new anticonvulsants, and clear guidelines for drug monitoring have yet to be defined. The antiepileptic drugs with the strongest justifications for drug monitoring are lamotrigine, oxcarbazepine, stiripentol, and zonisamide. Stiripentol and tiagabine are strongly protein bound and are candidates for free drug monitoring. Therapeutic drug monitoring has lower utility for gabapentin, pregabalin, and vigabatrin. Measurement of salivary drug concentrations has potential utility for therapeutic drug monitoring of lamotrigine, levetiracetam, and topiramate. Therapeutic drug monitoring of the new antiepileptic drugs will be discussed in managing patients with epilepsy.

Antiepileptic drug therapy in pregnancy II: fetal and neonatal exposure

The issue of how much an antiepileptic drug (AED) crosses the placenta and relative safety of lactation in mothers receiving AEDs are common clinical questions. Educating potential mothers with epilepsy regarding available information is warranted so that informed decisions and any needed neonatal monitoring is performed. Unfortunately, there is still limited data regarding the degree in which anticonvulsants cross the placenta and penetrate into breast milk. There is a greater appreciation of the factors that influence AED passive transfer across the placenta and into breast milk, as well as factors that ultimately influence neonatal AED distribution. In general, women with epilepsy can have healthy babies even with significant placental exposure and can breast-feed their babies safely with some cautions. Phenobarbital and primidone should be avoided in parents wishing to breast-feed. For the AEDs ethosuximide, levetiracetam, lamotrigine, topiramate, and zonisamide, there is a potential for significant breast milk concentrations; however, there are no firm guidelines on whether lactation is safe. In all cases, parents should be counseled to monitor their child for side effects and the need for routine monitoring.

Antiepileptic drugs--best practice guidelines for therapeutic drug monitoring: a position paper by the subcommission on therapeutic drug monitoring, ILAE Commission on Therapeutic Strategies

Although no randomized studies have demonstrated a positive impact of therapeutic drug monitoring (TDM) on clinical outcome in epilepsy, evidence from nonrandomized studies and everyday clinical experience does indicate that measuring serum concentrations of old and new generation antiepileptic drugs (AEDs) can have a valuable role in guiding patient management provided that concentrations are measured with a clear indication and are interpreted critically, taking into account the whole clinical context. Situations in which AED measurements are most likely to be of benefit include (1) when a person has attained the desired clinical outcome, to establish an individual therapeutic concentration which can be used at subsequent times to assess potential causes for a change in drug response; (2) as an aid in the diagnosis of clinical toxicity; (3) to assess compliance, particularly in patients with uncontrolled seizures or breakthrough seizures; (4) to guide dosage adjustment in situations associated with increased pharmacokinetic variability (e.g., children, the elderly, patients with associated diseases, drug formulation changes); (5) when a potentially important pharmacokinetic change is anticipated (e.g., in pregnancy, or when an interacting drug is added or removed); (6) to guide dose adjustments for AEDs with dose-dependent pharmacokinetics, particularly phenytoin.

Therapeutic Monitoring of Antiepileptic Drugs: A Comparison Between a Czech and a Swedish University Hospital

Plasma concentrations obtained during routine therapeutic monitoring of antiepileptic drugs (AED) (N03A ATC group) were compared in patients treated with one or several AED in the University Hospitals in Ostrava, Czech Republic and Huddinge, Sweden. Request and reply forms for therapeutic drug monitoring (TDM) were used as a source of mean plasma concentrations (PC). The study included 2,824 adult out- and inpatients in Huddinge treated from 1995 to 1999 and 1,268 outpatients treated in Ostrava from 1993 to 2004. PC of valproic acid in Huddinge and all AED except clonazepam in Ostrava were analyzed with gas-liquid chromatography. Plasma concentrations of clonazepam in Ostrava and all AED except valproic acid in Huddinge were analyzed by HPLC. The differences in PC were tested by Student's t-test. Chi(2) method was used for the differences in the distribution of PC relative to the therapeutic window. The mean plasma concentrations generally reached the apparent therapeutic ranges but were below the range in the cases of phenytoin monotherapy in both hospitals, and clonazepam, phenobarbital and phenytoin in polytherapy in Ostrava. In monotherapy 33% of the analyses showed sub-therapeutic concentrations in Huddinge, compared to 38% in Ostrava. Eight percent of the analyses showed potentially toxic concentrations in Huddinge, but only 3% in Ostrava. The highest number of sub-therapeutic concentrations was detected for phenytoin in both hospitals: 59% in Huddinge, 78% in Ostrava. In polytherapy only slight differences between the hospitals were found. PC/dose ratios were significantly lower in polytherapy than in monotherapy for carbamazepine and valproic acid in both hospitals. In contrast a higher PC/dose ratio was found in polytherapy for phenytoin in both cohorts and for lamotrigine in Ostrava. Drug treatment of epilepsy in our two hospitals is surprisingly similar in terms of achieved plasma concentrations, in spite of socioeconomic and cultural differences between our two countries. This may be explained by the long experience with TDM in both hospitals, which has the inherent capacity to promote evidence based drug therapy.

Analgesia and sedation during mechanical ventilation in neonates

BACKGROUND

Endotracheal intubation and mechanical ventilation are major components of routine intensive care for very low birth weight newborns and sick full-term newborns. These procedures are associated with physiologic, biochemical, and clinical responses indicating pain and stress in the newborn. Most neonates receive some form of analgesia and sedation during mechanical ventilation, although there are marked variations in clinical practice. Clinical guidelines for pharmacologic analgesia and sedation in newborns based on robust scientific data are lacking, as are measures of clinical efficacy.

OBJECTIVE

This article represents a preliminary attempt to develop a scientific rationale for analgesia sedation in mechanically ventilated newborns based on a systematic analysis of published clinical trials.

METHODS

The current literature was reviewed with regard to the use of opioids (fentanyl, morphine, diamorphine), sedative-hypnotics (midazolam), nonsteroidal anti-inflammatory drugs (ibuprofen, indomethacin), and acetaminophen in ventilated neonates. Original meta-analyses were conducted that collated the data from randomized clinical comparisons of morphine or fentanyl with placebo, or morphine with fentanyl.

RESULTS

The results of randomized trials comparing fentanyl, morphine, or midazolam with placebo, and fentanyl with morphine were inconclusive because of small sample sizes. Meta-analyses of the randomized controlled trials indicated that morphine and fentanyl can reduce behavioral and physiologic measures of pain and stress in mechanically ventilated preterm neonates but may prolong the duration of ventilation or produce other adverse effects. Randomized trials of midazolam compared with placebo reported significant adverse effects (P < 0.05) and no apparent clinical benefit; the findings of a meta-analysis suggest that there are insufficient data to justify use of IV midazolam for sedation in ventilated neonates.

CONCLUSIONS

Despite ongoing research in this area, huge gaps in our knowledge remain. Well-designed and adequately powered clinical trials are needed to establish the safety, efficacy, and short- and long-term outcomes of analgesia and sedation in the mechanically ventilated newborn.

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

In recent years, several new-generation antiepileptic drugs (AEDs) have been introduced in clinical practice. These agents, which include felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, pregabalin, tiagabine, topiramate, vigabatrin and zonisamide, are being increasingly used in the treatment of epilepsy at the extremes of age. For a rational prescribing of these drugs in specific age groups, major pharmacokinetic changes that occur during development and aging need to be taken into consideration. A review of available evidence indicates that the apparent oral clearance (CL/F) of new-generation AEDs in children is increased by 20-170% (depending on the type of drug and characteristics of the patients studied) compared with adults, with the highest CL/F values usually being observed in the youngest age groups. These findings do not necessarily apply to the first weeks of life, when drug eliminating capacity is still undergoing maturation, as in the case of lamotrigine for which preliminary data suggest that CL/F in neonates aged <2 months can be much lower than in infants aged 2-12 months. At the other extreme of age, in the elderly, CL/F is almost invariably reduced (on average by 10-50%) compared with values found in non-elderly adults. Age-related CL/F changes, together with the large interindividual pharmacokinetic variability, contribute to the need for individualised dosage requirements in these patients. Measurement of serum drug concentrations can be useful as an aid to dosage individualization in these age groups but interpretation of therapeutic drug monitoring data should also take into account the possibility of age-related changes in pharmacodynamic sensitivity and, for neonates and the elderly, alterations in drug binding to serum proteins.

Pharmacokinetic Variability of Newer Antiepileptic Drugs

A new generation of antiepileptic drugs (AEDs) has reached the market in recent years with ten new compounds: felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, pregabalin, tiagabine, topiramate, vigabatrin and zonisamide. The newer AEDs in general have more predictable pharmacokinetics than older AEDs such as phenytoin, carbamazepine and valproic acid (valproate sodium), which have a pronounced inter-individual variability in their pharmacokinetics and a narrow therapeutic range. For these older drugs it has been common practice to adjust the dosage to achieve a serum drug concentration within a predefined 'therapeutic range', representing an interval where most patients are expected to show an optimal response. However, such ranges must be interpreted with caution, since many patients are optimally treated when they have serum concentrations below or above the suggested range. It is often said that there is less need for therapeutic drug monitoring (TDM) with the newer AEDs, although this is partially based on the lack of documented correlation between serum concentration and drug effects. Nevertheless, TDM may be useful despite the shortcomings of existing therapeutic ranges, by utilisation of the concept of 'individual reference concentrations' based on intra-individual comparisons of drug serum concentrations. With this concept, TDM may be indicated regardless of the existence or lack of a well-defined therapeutic range. The ten newer AEDs all have different pharmacological properties, and therefore, the usefulness of TDM for these drugs has to be assessed individually. For vigabatrin, a clear relationship between drug concentration and clinical effect cannot be expected because of its unique mode of action. Therefore, TDM of vigabatrin is mainly to check compliance. The mode of action of the other new AEDs would not preclude the applicability of TDM. For the prodrug oxcarbazepine, TDM is also useful, since the active metabolite licarbazepine is measured. For drugs that are eliminated renally completely unchanged (gabapentin, pregabalin and vigabatrin) or mainly unchanged (levetiracetam and topiramate), the pharmacokinetic variability is less pronounced and more predictable. However, the dose-dependent absorption of gabapentin increases its pharmacokinetic variability. Drug interactions can affect topiramate concentrations markedly, and individual factors such as age, pregnancy and renal function will contribute to the pharmacokinetic variability of all renally eliminated AEDs. For those of the newer AEDs that are metabolised (felbamate, lamotrigine, oxcarbazepine, tiagabine and zonisamide), pharmacokinetic variability is just as relevant as for many of the older AEDs. Therefore, TDM is likely to be useful in many clinical settings for the newer AEDs. The purpose of the present review is to discuss individually the potential value of TDM of these newer AEDs, with emphasis on pharmacokinetic variability.

Management of Focal-Onset Seizures

Focal-onset seizures are manifestations of abnormal epileptic firing of brain cells in a localised area or areas of the brain. The diagnosis of focal-onset seizures initially entails an EEG, a detailed history from the patient and eyewitnesses, as well as computer tomographic or, preferably, magnetic resonance imaging scans. Video EEG to record ictal events may be necessary to establish the correct diagnosis. Focal seizures are classified according to the International Classification of Epileptic Seizures and International Classification of Epilepsies and Epilepsy Syndromes. It is important to try to decide how the seizure event fits into this system in order to successfully evaluate and optimise treatment, as well as to give detailed information to the patient about their seizures and prognosis. Once the decision to treat the seizures has been made, the physician must choose which medication is the most appropriate to begin with. Carbamazepine, phenytoin or valproic acid (sodium valproate) are often rated as first-line drugs, but factors such as adverse-effect profiles, age, possibility of pregnancy, and concomitant diseases and medication also need to be considered. Most of the newer antiepileptic drugs (AEDs) appear to have good efficacy and better tolerability than the older agents, but evidence to support their superiority is scarce and has led to conflicting advice in several guidelines. Among the newer AEDs, lamotrigine, gabapentin, topiramate and oxcarbazepine have obtained monotherapy indication in many countries. The higher costs of the newer AEDs may inhibit their wider use, especially in poorer countries.

Unusual presentation of iatrogenic phenytoin toxicity in a newborn

BACKGROUND

Medication errors may produce severe toxicity resulting in hospitalization. This can be compounded if the physician obtains the wrong concentration from a reference manual and a pharmacy miscalculates the conversion. We report a child presenting with ileus, hypothermia and lethargy after receiving supratherapeutic dosing of phenytoin after a concentration miscalculation.

CASE REPORT

A one-month-old infant presented to the Emergency Department with progressive worsening of abdominal distension, diminished activity, and a one day history of difficulty feeding secondary to a decreased level of consciousness. The past medical history was significant for neonatal Group B Strep meningitis with seizures. Among the child's discharge medications was a prescription for phenytoin (30 mg/5 mL) 2.5 cc by mouth three times daily. On exam, the child was hypothermic with pink mottled skin, poor responsiveness, prolonged capillary refill, abdominal distension with hypoactive bowel sounds, and a dysconjugate gaze. The Initial phenytoin serum concentration was 91.8 mcg/mL. She was admitted to the PICU and was started on ampicillin and cefotaxime for R/O sepsis. Phenytoin was withheld and subsequent serum concentrations revealed an extremely slow elimination (mcg/mL vs. time pair coordinates were 78.2/13.3h; 74.3/62.3h; 43.7/109.6h; 10.8/160.9h) reflecting zero-order kinetics. Post discontinuing antibiotics, phenytoin levels decreased at rates expected. She was discharged after resolution of symptoms. The MD who had written the phenytoin prescription had based it on the Harriet Lane Handbook, 2000 Ed. The 30 mg/5 mL formulation has been unavailable in the US for several years. A community pharmacy substituted the 125 mg/5 mL formulation, but miscalculated the dosage to be 1.6 cc (40 mg) tid.

CONCLUSIONS

Abdominal distension and ileus may be presenting symptoms in children at toxic phenytoin levels. Ampicillin and cefotaxime may effect the elimination rate of phenytoin at such levels. We report one of the highest phenytoin levels recorded after therapeutic misadventure. Physicians must be aware of inaccuracies in reference manuals that may result in dosing errors.

HLA-B genotyping to detect carbamazepine-induced Stevens-Johnson syndrome: implications for personalizing medicine

Preventing severe adverse drug reactions by identifying people at risk with a simple genetic test is the goal of many pharmacogenomic studies. Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are related, life-threatening cutaneous adverse reactions, most often caused by medication. The overall incidence and the commonly offending drugs vary among different ethnic populations. Susceptibility to such idiosyncratic reactions is thought to be genetically determined and immune mediated. Finding a strong genetic association between a particular human leukocyte antigen (HLA)-B allele and the reaction to a specific drug provides evidence that the pathogenesis of the severe cutaneous adverse drug reactions involves major histocompatibility complex-restricted presentation of a drug or its metabolites for T-cell activation. In the case of carbamazepine-induced SJS/TEN, the tight association of the HLA-B*1502 allele (sensitivity 100%, specificity 97% and odds ratio 2504) provides a plausible basis for further development of such a test to identify individuals at risk of developing this life-threatening condition.

Pharmacological and behavioral characteristics of interactions between vigabatrin and conventional antiepileptic drugs in pentylenetetrazole-induced seizures in mice: an isobolographic analysis

To characterize the anticonvulsant effects and types of interactions exerted by mixtures of vigabatrin (VGB) and conventional antiepileptic drugs (valproate (VPA), ethosuximide (ESM), phenobarbital (PB), and clonazepam (CZP)) in pentylenetetrazole (PTZ)-induced seizures in mice, the isobolographic analysis for three fixed-ratio combinations of 1 : 3, 1 : 1, and 3 : 1 was used. The adverse-effect profile of the combinations tested, at the doses corresponding to their median effective doses (ED(50)) at the fixed-ratio of 1 : 1 against PTZ-induced seizures, was determined by the chimney (motor performance), step-through passive avoidance (long-term memory), pain threshold (pain sensitivity), and Y-maze (general explorative locomotor activity) tests in mice. Additionally, the observed isobolographic interactions were verified in terms of a pharmacokinetic interaction existence. VGB combined with PB or ESM exerted supra-additive (synergistic) interactions against the clonic phase of PTZ-induced seizures, which was associated with the increment of PB or ESM concentrations in the brains of examined animals. The remaining combinations tested (ie VGB+VPA and VGB+CZP) occurred additive in the PTZ test, which was associated with no significant changes in the brain concentrations of VPA and CZP. None of the examined combinations exerted motor impairment in the chimney test in mice. In the standard variant of passive avoidance task (current of 0.6 mA; 2 s of stimulus duration), the combinations of VGB+CZP and VGB+VPA significantly affected long-term memory in mice. Moreover, VGB in a dose-dependent manner lengthened the latency to the first pain reaction in the pain threshold test in mice. The modified variant of step-through passive avoidance task (current of 0.6 mA; stimulus duration based on the latency from the pain threshold test) revealed no significant changes in the long-term memory of animals for the combinations of VGB+VPA and VGB+CZP; so the observed effects in the standard variant of passive avoidance task were a result of the antinociceptive effects produced by VGB. In the Y-maze test, VGB also, in a dose-dependent manner, increased the general explorative locomotor activity of the animals tested. Similarly, the total number of arm entries in the Y-maze was significantly increased for the combinations of VGB+CZP and VGB+ESM, but not for VGB+PB and VGB+VPA. The application of VGB in combination with PB, ESM, CZP, and VPA suppressed the clonic phase of PTZ-induced seizures, having no harmful or deleterious effects on behavioral functioning of the animals tested, which might be advantageous in further clinical practice.

Pharmacokinetic considerations in the treatment of childhood epilepsy

Organogenesis throughout childhood affects almost every aspect of pediatric pharmacotherapy. The antiepileptic drugs (AEDs) are particularly impacted since most elimination rates are diminished for the first 6 months of infancy, but quickly attain and supersede adult values. When children enter a hypermetabolic stage, large doses of AEDs may be necessary to maintain effective serum concentrations. Medication noncompliance is frequently confused as hypermetabolism, since both present with low serum drug concentrations. Amazingly, noncompliance among children with chronic illness approaches a similar incidence to that reported in the adult population. It is obviously important to include this in the differential diagnosis of the etiology of subtherapeutic serum AED concentrations. Maturational differences also affect gastrointestinal drug absorption. Intestinal transit time and absorptive surface area are both diminished in young children. Drug delivery systems suitable in adults may not deliver the total dosage in children. Differences in the composition of body compartments and protein binding can alter the volume of drug distribution and, consequently, serum concentrations. In addition to pathophysiologic changes, there is evidence to suggest differences between a mature and immature brain. These differences include quantitative and qualitative responses to neurotransmitters. Hence, it is understandable why seizure semiology is different in children compared with adults. This constellation of factors contributes to the challenges of caring for children with epilepsy.

Contribution of functional voltage-gated Na+ channel expression to cell behaviors involved in the metastatic cascade in rat prostate cancer: I. Lateral motility

Previous work suggested that functional voltage-gated Na(+) channels (VGSCs) are expressed specifically in strongly metastatic cells of rat and human prostate cancer (PCa), thereby raising the possibility that VGSC activity could be involved in cellular behavior(s) related to the metastatic cascade. In the present study, the possible role of VGSCs in the lateral motility of rat PCa cells was investigated in vitro by testing the effect of modulators that either block or enhance VGSC activity. Two rat PCa cell lines of markedly different metastatic ability were used in a comparative approach: the strongly metastatic MAT-LyLu and the weakly metastatic AT-2 cell line, only the former being known to express functional VGSCs. Using both electrophysiological recording and a motility assay, the effects of two VGSC blockers (tetrodotoxin and phenytoin) and four potential openers (veratridine, aconitine, ATX II, and brevetoxin) were monitored on (a) Na(+) channel activity and (b) cell motility over 48 h. Tetrodotoxin (at 1 microM) and phenytoin (at 50 microM) both decreased the motility index of the MAT-LyLu cell line by 47 and 11%, respectively. Veratridine (at 20 microM) and brevetoxin (at 10 nM) had no effect on the motility of either cell line, whilst aconitine (at 100 microM) and ATX II (at 25 pM) significantly increased the motility of the MAT-LyLu cell line by 15 and 9%, respectively. Importantly, at the concentrations used, none of these drugs had effects on the proliferation or viability of either cell line. The results, taken together, would suggest strongly that functional VGSC expression enhances cellular motility of PCa cells. The relevance of these findings to the metastatic process in PCa is discussed.

Therapeutic drug monitoring of the newer antiepileptic drugs

The aim of the present review is to discuss the potential value of therapeutic drug monitoring (TDM) of the newer antiepileptic drugs (AEDs) felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine, topiramate, vigabatrin, and zonisamide. Studies of the relationship between serum concentrations and clinical efficacy of these drugs are reviewed, and the potential value of TDM of the drugs is discussed based on their pharmacokinetic properties and mode of action. Analytical methods for the determination of the serum concentrations of these drugs are also briefly described. There are only some prospective data on the serum concentration-effect relationships, and few studies have been designed primarily to study these relationships. As TDM is not widely practiced for the newer AEDs, there are no generally accepted target ranges for any of these drugs, and for most a wide range in serum concentration is associated with clinical efficacy. Furthermore, a considerable overlap in drug concentrations related to toxicity and nonresponse is reported. Nevertheless, the current tentative target ranges for felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine (10-hydroxy-carbazepine metabolite), tiagabine, topiramate, vigabatrin, and zonisamide are 125 to 250 micromol/L, 70 to 120 micromol/L, 10 to 60 micromol/L, 35 to 120 micromol/L, 50 to 140 micomol/L, 50 to 250 nmol/L, 15 to 60 micromol/L, 6 to 278 micromol/L, and 45 to 180 micromol/L, respectively. Further systematic studies designed specifically to evaluate concentration-effect relationships of the new AEDs are urgently needed. Although routine monitoring in general cannot be recommended at present, measurements of some of the drugs is undoubtedly of help with individualization of treatment in selected cases in a particular clinical setting.

Children versus adults: pharmacokinetic and adverse-effect differences

Pharmacokinetic differences may play a part in the age-related differences in the incidence of adverse effects. The most common idiosyncratic reaction to lamotrigine (LTG) is rash, affecting 10-20% of patients. Risk factors are young age, concurrent valproate (VPA), high starting dose, and rapid escalation. In children, cytochrome P450 (CYP)-catalyzed metabolism is increased, and uridine diphosphate (UDP)-glucuronosyltransferase (UGT)-catalyzed metabolism is not significantly different from that in adults. A CYP-catalyzed arene oxide intermediate of LTG has been identified. The increase CYP metabolism of LTG in children could result in increased formation of the reactive metabolite and a higher incident of rash. Children often received higher milligram per kilogram doses compared with adults. The higher dose would cause an increased amount of LTG metabolized to the reactive arene oxide intermediate. VPA therapy is associated with a transient elevation in liver-function tests in 15-30% of patients and a rare, fatal hepatotoxicity. Most cases of VPA hepatotoxicity occurred in children younger than 2 years who had preexisting neurologic or other physical defects. Hypotheses regarding the pathogenesis of the hepatotoxicity include preexisting mitochondrial disease or inborn errors of metabolism, VPA inhibition of beta-oxidation, and toxicity from VPA metabolites VPA, 4-ene-VPA, and 2,4-diene-VPA. Infants and children have higher concentration ratios of 4-ene-VPA to VPA. Polytherapy with enzyme inducers increases the formation of the hepatotoxic metabolites. The role of underlying metabolic disorders associated with hepatodegeneration and intractable seizures without VPA is a major confounder in identifying risk factors and demonstrates the difficulty in separating underlying disease factors in rare idiosyncratic reactions.

Time course of lamotrigine de-induction: impact of step-wise withdrawal of carbamazepine or phenytoin

OBJECTIVE

The objective of the present analysis is to examine lamotrigine (LTG) pharmacokinetics both during polytherapy with enzyme inducing antiepileptic drugs and to evaluate the time course of de-induction following the step-wise withdrawal of enzyme inducers.

BACKGROUND

LTG pharmacokinetics can be significantly influenced by concomitant AEDs, and the addition of enzyme inducers can markedly increase LTG clearance, thereby reducing serum concentrations. A clinically relevant question is how will LTG clearance and resulting plasma concentrations be altered during concomitant enzyme inducer withdrawal/conversion process.

DESIGN/METHOD

As part of a previously published, active-control, LTG monotherapy trial, dose and plasma concentration data for LTG, carbamazepine (CBZ) or phenytoin (PHT) were obtained. Following the attainment of a LTG target dose of 500 mg/day, CZB or PHT were withdrawn in weekly 20% decrements. Following inducer withdrawal, LTG was then continued as monotherapy for an additional 12 weeks. Plasma concentrations and daily doses of LTG, CBZ, or PHT were obtained at regularly scheduled study visits during inducer withdrawal and during LTG monotherapy. Pharmacokinetic analysis of the plasma concentration data was done to determine the time-course and effect of inducer plasma concentration on LTG oral clearance (Cl(o)), where LTG Cl(o) was estimated as the dose/concentration ratio.

RESULTS

Of the 156 patients enrolled in this trial, 76 were assigned to LTG arm, 43 completed the withdrawal to monotherapy phase with 28 successfully completing the study. In a subset analysis of completers, LTG Cl(o) determined prior to withdrawal of the inducers was significantly greater in patients (n=28) on LTG+PHT (160% increase) than in those (n=48) receiving LTG+CBZ (62% increase): 1.77+/-0.77 vs. 1.06+/-0.41 ml/min/kg, respectively, p=0.017. The significant reduction in LTG Cl(o) occurred only when CBZ plasma concentrations reached approximately 2 microg/ml or PHT plasma concentrations reached zero.

CONCLUSIONS

Mean LTG plasma concentrations will approximately double following the withdrawal PHT; however increases of only 60% may occur following the withdrawal of CBZ. Importantly, these data suggest that LTG concentrations would not be expected to increase until the concomitant inducer is almost completely removed.

Incidence of epilepsies and epileptic syndromes in children and adolescents: a population-based prospective study in Germany

PURPOSE

To estimate the incidence rate of epilepsies and epileptic syndromes in German children and adolescents aged 1 month to <15 years, and to provide data on their classification.

METHODS

A population-based prospective study was performed between July 1, 1999, and June 30, 2000. All children aged 1 month to <15 years with a newly diagnosed epilepsy or epileptic syndrome were recorded by private pediatricians, EEG laboratories, and the two University Children's Hospitals in the neighboring cities of Heidelberg and Mannheim. The diagnoses were classified according to the International Classification of Epilepsies and Epileptic Syndromes of the International League Against Epilepsy (ILAE).

RESULTS

The total age-adjusted annual incidence rate was 60/100,000 (95% confidence interval, 42-84), with the highest incidence in the first year of life (146/100,000). Focal epilepsies or epileptic syndromes (58%; incidence rate, 35/100,000) were more common than were generalized ones (39%; incidence rate, 24/100,000), and 3% (incidence rate, 2/100,000) of the epilepsies or epileptic syndromes were undetermined. The rate of idiopathic (47%; incidence rate, 29/100,000) and symptomatic or cryptogenic epilepsies (50%; incidence rate, 30/100,000) was equal. No significant difference in incidence between boys and girls was found.

CONCLUSIONS

Incidence rates for epilepsy in German children aged 1 month to <15 years are about equal to those of other countries in Europe and North America. In accordance with studies from the United States and from many European countries, incidence was highest in the first year of life, and no difference in the incidence between girls and boys was found. In Germany as throughout Europe, idiopathic generalized epileptic syndromes are more often diagnosed than in the United States.

Oxcarbazepine in the treatment of epilepsy

Oxcarbazepine is a new antiepileptic drug (AED) that has been registered in more than 50 countries worldwide since 1990 and recently received approval in the United States and the European Union. Oxcarbazepine is a keto analog of carbamazepine and has a more favorable pharmacokinetic profile. It is rapidly absorbed after oral administration and undergoes rapid and almost complete reductive metabolism to form the pharmacologically active 10-monohydroxy derivative. Oxcarbazepine exhibits linear pharmacokinetics, no autoinduction, and minimal interaction with other AEDs. Ten controlled trials demonstrated that oxcarbazepine is safe and efficacious in the treatment of partial seizures across a wide range of ages (children to adults), situations (recent onset to treatment-resistant epilepsy), and uses (monotherapy and adjunctive therapy). The most common treatment-emergent adverse events are related to the central nervous system. Treatment-emergent hyponatremia (defined as serum sodium level < 125 mEq/L) occurred in 3% of patients treated with oxcarbazepine in clinical trials. According to the efficacy and safety profile established in the controlled trials, oxcarbazepine represents an important new treatment option indicated for monotherapy and adjunctive therapy in adults with partial seizures and as adjunctive therapy in children aged 4 years or older with partial seizures. Although structurally similar to carbamazepine, significant differences exist in the pharmacokinetics, drug interaction potential, adverse-effect profile, and dosage and titration between these two agents, and they should be considered distinct therapeutic agents.

Comparison of the effect of fish oil and corn oil on chemical-induced hepatic enzyme-altered foci in rats

The effects of fish oil and corn oil diets on diethylnitrosamine initiation/phenobarbital promotion of hepatic enzyme-altered foci in female Sprague-Dawley rats were investigated. Groups of 12 rats were initiated with diethylnitrosamine (15 mg/kg) at 24 h of age. After weaning, they received diets containing either 13.5% fish oil plus 1. 5% corn oil or 15% corn oil for 24 weeks. Rats fed fish oil had significantly greater liver weight, relative liver weight, spleen weight, and relative spleen weight than rats fed corn oil (p < 0.05). Hepatic phospholipid fatty-acid profile was significantly affected by the type of dietary lipid. The rats fed fish oil had significantly greater hepatic phospholipid 20:5 and 22:6 than rats fed corn oil; in contrast, the rats fed corn oil had significantly greater hepatic phospholipid 18:2 and 20:4 than rats fed fish oil (p < 0.05). Rats fed fish oil had significantly lower hepatic vitamin E and PGE(2) content but significantly greater hepatic lipid peroxidation than rats fed corn oil (p < 0.05). The hepatic levels of antioxidant enzymes (GSH reductase and GST) were significantly greater in rats fed fish oil than in rats fed corn oil (p < 0.05). Except for PGST-positive foci (foci area/tissue area), all the other foci parameters (GGT-positive foci area/tissue area, GGT-positive foci no./cm(2), GGT-positive foci no./cm(3), PGST-positive foci no. /cm(2), and PGST-positive foci no./cm(3)) measured in the fish oil group were 10-30% of those in the corn oil group (p < 0.05). Analyses of Pearson correlation coefficient revealed a positive correlation between hepatic GGT- or PGST-positive foci number (no. /cm(2)) and PGE(2) content (r = 0.66, P = 0.01; r = 0.56, P = 0.02, respectively) but a negative correlation between GGT- and PGST-positive foci (no./cm(2)) and lipid peroxidation (r = -0.8, P = 0.0006; r = -0.58, P = 0.01, respectively), GSH/(GSH + GSSG) ratio (r = -0.61, P = 0.05; r = -0.4, P = 0.14, respectively), GSH reductase (r = -0.75, P = 0.002; r = -0.53, P = 0.02, respectively), and GST activities (r = -0.65, P = 0.01; r = -0.44, P = 0.07, respectively). Similar correlation between foci number (no./cm(3)) and PGE(2), lipid peroxidation, GSH/(GSH + GSSG) ratio, GSH reductase, and GST activities were obtained. The results of this study show that dietary fish oil significantly inhibited hepatic enzyme-altered foci formation compared with corn oil in rats. These results suggest that the possible mechanisms involved in this process are the stimulation of hepatic detoxification system, changes in membrane composition, inhibition of PGE(2) synthesis, the enhancement of GSH-related antioxidant capacity, and the enhancement of lipid peroxidation by fish oil.