The clinical pharmacokinetics of the newer antiepileptic drugs. Focus on topiramate, zonisamide and tiagabine

A new population pharmacokinetic model for dosing optimization of zonisamide in patients with refractory epilepsy

Zonisamide exhibits significant pharmacokinetic variability, demanding for the development of population pharmacokinetic (PopPK) models to identify key factors influencing drug disposition. This study aimed to develop and validate a PopPK model to optimize zonisamide posology in patients with refractory epilepsy. A total of 114 plasma concentrations of zonisamide, obtained from 64 patients, were used for PopPK model development, employing the nonlinear mixed-effects modelling approach. The final model was evaluated by visually inspecting the goodness-of-fit plots and the visual predictive check plot and by the bootstrap resampling method. A one-compartment model with first-order elimination was the one that best described the pharmacokinetic profile of zonisamide. Between-patient variability (BPV) was included on clearance (CL/F), volume of distribution (Vd/F) and absorption rate constant (ka). The residual error (RE) was modeled as proportional. The final model estimates for CL/F, Vd/F and ka were 0.761 L/h, 48.10 L and 0.671 h⁻¹, respectively. The BPV associated with CL/F, Vd/F, and ka was 43.93%, 52.06%, and 91.27%, respectively, while the proportional RE was 7.18%. The concomitant administration of enzyme-inducing antiseizure drugs (EIASDs), included in the model as inducer drug load (INDDL), significantly accounted for BPV associated with CL/F and led to increased CL/F in patients receiving EIASDs compared to the others. Consequently, patients receiving EIASDs require higher daily doses of zonisamide to achieve therapeutic plasma concentrations compared to those not treated with EIASDs. Model validation, using bootstrap and visual predictive checks, confirmed its stability and robustness, making it a valuable tool for individualized zonisamide dosing in adults with refractory epilepsy.

Development of SV2A Ligands for Epilepsy Treatment: A Review of Levetiracetam, Brivaracetam, and Padsevonil

Epilepsy is a common neurological disorder that is primarily treated with antiseizure medications (ASMs). Although dozens of ASMs are available in the clinic, approximately 30% of epileptic patients have medically refractory seizures; other limitations in most traditional ASMs include poor tolerability and drug-drug interactions. Therefore, there is an urgent need to develop alternative ASMs. Levetiracetam (LEV) is a first-line ASM that is well tolerated, has promising efficacy, and has little drug-drug interaction. Although it is widely accepted that LEV acts through a unique therapeutic target synaptic vesicle protein (SV) 2A, the molecular basis of its action remains unknown. Even so, the next-generation SV2A ligands against epilepsy based on the structure of LEV have achieved clinical success. This review highlights the research and development (R&D) process of LEV and its analogs, brivaracetam and padsevonil, to provide ideas and experience for the R&D of novel ASMs.

Tiagabine and zonisamide differentially regulate the glial properties in an astrocyte-microglia co-culture model of inflammation

Due to the role of astrocytes and microglia in the pathophysiology of epilepsy and limited studies of antiseizure medication (ASM) effects on glial cells, we studied tiagabine (TGB) and zonisamide (ZNS) in an astrocyte-microglia co-culture model of inflammation. Different concentrations of ZNS (10, 20, 40, 100 µg/ml) or TGB (1, 10, 20, 50 µg/ml) were added to primary rat astrocytes co-cultures with 5-10% (M5, physiological conditions) or 30-40% (M30, pathological inflammatory conditions) microglia for 24 h, aiming to study glial viability, microglial activation, connexin 43 (Cx43) expression and gap-junctional coupling. ZNS led to the reduction of glial viability by only 100 µg/ml under physiological conditions. By contrast, TGB revealed toxic effects with a significant, concentration-dependent reduction of glial viability under physiological and pathological conditions. After the incubation of M30 co-cultures with 20 µg/ml TGB, the microglial activation was significantly decreased and resting microglia slightly increased, suggesting possible anti-inflammatory features of TGB under inflammatory conditions. Otherwise, ZNS caused no significant changes of microglial phenotypes. The gap-junctional coupling was significantly decreased after the incubation of M5 co-cultures with 20 and 50 µg/ml TGB, which can be related to its anti-epileptic activity under noninflammatory conditions. A significant decrease of Cx43 expression and cell-cell coupling was found after the incubation of M30 co-cultures with 10 µg/ml ZNS, suggesting additional anti-seizure effects of ZNS with the disruption of glial gap-junctional communication under inflammatory conditions. TGB and ZNS differentially regulated the glial properties. Developing novel ASMs targeting glial cells may have future potential as an "add-on" therapy to classical ASMs targeting neurons.

Development and Validation of a Simple HPLC-UV Assay Method for Determination of Levetiracetam Concentrations in Human Plasma

Levetiracetam (LEV) is a broad spectrum antiseizure medication that is used in various seizure types. There is evidence that therapeutic drug monitoring (TDM) of LEV is of value in selected patient populations, therefore determination of LEV plasma concentrations is essential. Herein we developed and validated a simple, reproducible, and practical method for the quantification of LEV concentrations in human plasma samples using high performance liquid chromatography (HPLC). Plasma samples (0.3 mL) deproteinization was done using acetonitrile. HPLC chromatographic separation of plasma samples was accomplished by reversed phase C18 column. The mobile phase constituted water and acetonitrile (90:10, v/v) ran at flow rate of 1 mL/min. Signal acquisition was conducted at a wavelength of 192 nm. Calibration curves showed excellent linearity (Correlation coefficient r2 > 0.99) over a concentration range of 3–80 μg/mL. Both inter and intraday assay accuracy and precision were less than 8% (except for the lowest limit of quantification was within 20%). Elution time was 15 min. The developed method excluded the use of buffers and utilized small volumes of plasma samples with simple mobile phase composition. Therefore, our method could be practically applied to routine TDM.

Off-label and investigational drugs in the treatment of alcohol use disorder: A critical review

Compounds known to be successful in the treatment of alcohol use disorder include the aversive agent, Disulfiram, the glutamatergic NMDA receptor antagonist, Acamprosate, and the opioid receptor antagonists, Naltrexone and Nalmefene. Although all four are effective in maintaining abstinence or reduction of alcohol consumption, only a small percentage of patients receive pharmacological treatment. In addition, many other medications have been investigated for their therapeutic potential in the treatment of alcohol use disorder. In this review we summarize and compare Baclofen, Gabapentin, Topiramate, Ondansetron, Varenicline, Aripiprazole, Quetiapine, Clozapine, Antidepressants, Lithium, Neuropeptide Y, Neuropeptide S, Corticotropin-releasing factor antagonists, Oxytocin, PF-05190457, Memantine, Ifenprodil, Samidorphan, Ondelopran, ABT-436, SSR149415, Mifepristone, Ibudilast, Citicoline, Rimonabant, Surinabant, AM4113 and Gamma-hydroxybutyrate While some have shown promising results in the treatment of alcohol use disorder, others have disappointed and should be excluded from further investigation. Here we discuss the most promising results and highlight medications that deserve further preclinical or clinical study. Effective, patient-tailored treatment will require greater understanding provided by many more preclinical and clinical studies.

Topiramate intoxications & hemodialysis - Literature review and the first case report of a massive suicidal intoxication treated with hemodialysis

BACKGROUND

Topiramate is an anticonvulsant from sulfamate-substituted monosaccharides that is increasingly used to treat migraines. Serious topiramate intoxications have been described. Unfortunately, indications for and the effect of interventions, including hemodialysis, in severe intoxications seem expert-based and lack empirical evidence. We aim to review the literature on topiramate intoxication cases and to describe the first topiramate intoxication with toxicokinetic data following treatment with hemodialysis.

METHODS

A literature review was conducted using the PubMed database. Included articles were reviewed for symptoms; management, including acute hemodialysis; toxicokinetic data; and outcomes.

RESULTS

We found 61 hits in the PubMed database and checked 392 references in the snowball search; 22 were included for data extraction, reporting 29 cases. The majority of the patients were female (n = 23/29, 79%), ranging in age from 2 to 44 years (median 21). The ingested topiramate amount ranged from 175 to 40,000 mg (usual maintenance dose of 50 mg BID and a general maximum of 500 mg BID). Topiramate concentrations were reported in eight cases, ranging from 3.7 to 356.6 mg/L (for reference, the therapeutic range is 2-30 mg/L). Serious topiramate intoxications can result in seizures, coma, hemodynamic instability and severe metabolic acidosis. In no single case was hemodialysis used.

CONCLUSION

Serious symptoms of topiramate intoxications exist, and hemodialysis is used infrequently. If symptoms are refractory to symptomatic treatment, hemodialysis can reduce topiramate concentrations and symptomatology.

Treatment and care of women with epilepsy before, during, and after pregnancy: a practical guide

Women with epilepsy (WWE) wishing for a child represent a highly relevant subgroup of epilepsy patients. The treating epileptologist needs to delineate the epilepsy syndrome and choose the appropriate anti-seizure medication (ASM) considering the main goal of seizure freedom, teratogenic risks, changes in drug metabolism during pregnancy and postpartum, demanding for up-titration during and down-titration after pregnancy. Folic acid or vitamin K supplements and breastfeeding are also discussed in this review. Lamotrigine and levetiracetam have the lowest teratogenic potential. Data on teratogenic risks are also favorable for oxcarbazepine, whereas topiramate tends to have an unfavorable profile. Valproate needs special emphasis. It is most effective in generalized seizures but should be avoided whenever possible due to its teratogenic effects and the negative impact on neuropsychological development of in utero-exposed children. Valproate still has its justification in patients not achieving seizure freedom with other ASMs or if a woman decides to or cannot become pregnant for any reason. When valproate is the most appropriate treatment option, the patient and caregiver must be fully informed of the risks associated with its use during pregnancies. Folate supplementation is recommended to reduce the risk of major congenital malformations. However, there is insufficient information to address the optimal dose and it is unclear whether higher doses offer greater protection. There is currently no general recommendation for a peripartum vitamin K prophylaxis. During pregnancy most ASMs (e.g. lamotrigine, oxcarbazepine, and levetiracetam) need to be increased to compensate for the decline in serum levels; exceptions are valproate and carbamazepine. Postpartum, baseline levels are reached relatively fast, and down-titration is performed empirically. Many ASMs in monotherapy are (moderately) safe for breastfeeding and women should be encouraged to do so. This review provides a practically oriented overview of the complex management of WWE before, during, and after pregnancy.

Determination of levetiracetam by GC-MS and effects of storage conditions and gastric digestive systems on drug samples

Background: Epilepsy is a neurologic condition that is occurs globally and is associated with various degrees of seizures. Levetiracetam is an approved drug that is commonly used to treat seizures in juvenile epileptic patients. Accurate quantification of the drug's active compound and determining its stability in the stomach after oral administration are important tasks that must be performed. Results & methodology: Levetiracetam was extracted from drug samples and quantified by gas chromatography mass spectrometry using calibration standards. Stability of levetiracetam was studied under various storage conditions and in simulated gastric conditions. The calibration plot determined for levetiracetam showed good linearity with a coefficient of determination value of 0.9991. The limits of detection and quantification were found to be 0.004 and 0.014 μg·ml^-1, respectively. The structural integrity of levetiracetam did not change within a 4-h period under the simulated gastric conditions, and no significant degradation was observed for the different storage temperatures tested. Discussion & conclusion: An accurate and sensitive quantitative method was developed for the determination of levetiracetam in drug samples. The stability of the drug active compound was monitored under various storage and gastric conditions. The levetiracetam content determined in the drug samples were within ±10% of the value stated on the drug labels.

Voltage gated sodium channel inhibitors as anticonvulsant drugs: A systematic review on recent developments and structure activity relationship studies

Voltage-gated sodium channel blockers are one of the vital targets for the management of several central nervous system diseases, including epilepsy, chronic pain, psychiatric disorders, and spasticity. The voltage-gated sodium channels play a key role in controlling cellular excitability. This reduction in excitotoxicity is also applied to improve the symptoms of epileptic conditions. The effectiveness of antiepileptic drugs as sodium channel depends upon the reversible blocking of the spontaneous discharge without blocking its propagation. There are number of antiepileptic drug(s) which are in pipeline to flour the market to conquer abnormal neuronal excitability. They inhibit the seizures through the inhibition of complex voltage- and frequency-dependent ionic currents through sodium channels. Over the past decade, the sodium channel is one of the most explored targets to control or treat the seizure, but there has not been any game-changing discovery yet. Although there are large numbers of drugs approved for the treatment of epilepsy, however they are associated with several acute to chronic side effects. Many research groups have tirelessly worked for better therapeutic medication on this popular target to treat epileptic seizures. The review quotes briefly the developments of the approved examples of sodium channel blockers as anticonvulsant drugs. Medicinal chemists have tried the design and development of some more potent anticonvulsant drugs to minimize the toxicity that are discussed here, and an emphasis is given for their possible mechanism and the structure-activity relationship (SAR).

Use of Topiramate in the Spectrum of Addictive and Eating Disorders: A Systematic Review Comparing Treatment Schemes, Efficacy, and Safety Features

BACKGROUND AND OBJECTIVE

Topiramate has been approved by the US Food and Drug Administration for the treatment of epilepsy since the 1990s, and it has also been used off-label in the treatment of many types of addictive disorders. To date, no systematic review has embraced the entire field of addiction, both substance use and behavioral addictions, including eating disorders, to compare topiramate-based protocols and the related level of evidence in each addictive disorder. Our objective is to fill this gap.

METHODS

A systematic search was conducted using the MEDLINE, PsycINFO, and Cochrane databases without a date or language limit. All trials and meta-analyses assessing the efficacy of topiramate in alcohol use disorder; cocaine use disorder; methamphetamine, nicotine, cannabis, opiate, and benzodiazepine use disorders; binge eating disorder; bulimia; and pathological gambling were analyzed. The quality of the studies was rated using the Cochrane Risk-of-Bias tool for randomized trials (ROB-2), the Risk of Bias In Nonrandomized Studies (ROBINS-I), or the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist, depending on the study design. Safety features were assessed based on a wider non-systematic review.

RESULTS

Sixty-two articles were reviewed. Treatment protocols were relatively homogenous across addictive disorders, with slow dose titration schemes and a maximum dose range of 200-400 mg per day. The most supportive evidence for topiramate efficacy was found in alcohol use disorder for drinking reduction parameters only. To a lesser extent, topiramate could be a promising therapeutic option for binge eating disorder and cocaine use disorder. Evidence was weak for other addictive disorders. No major tolerability issues were found, provided that basic safety rules were followed. Adverse drug reactions could lead to early treatment discontinuation.

DISCUSSION

Though off-label, addiction specialists should consider topiramate as a second-line option for drinking reduction in alcohol use disorder, as well as for binge eating disorder or cocaine use disorder.

Pharmacological management of dementia with Lewy bodies with a focus on zonisamide for treating parkinsonism

INTRODUCTION

Dementia with Lewy bodies (DLB) has no approved symptomatic or disease-modifying treatments in the US and Europe, despite being the second most common cause of neurodegenerative dementia.

AREAS COVERED

Herein, the authors briefly review the DLB drug development pipeline, providing a summary of the current pharmacological intervention studies. They then focus on the anticonvulsant zonisamide, a benzisoxazole derivative with a sulfonamide group and look at its value for treating parkinsonism in DLB.

EXPERT OPINION

Several new compounds are being tested in DLB, the most innovative being those aimed at decreasing brain accumulation of α-synuclein. Unfortunately, new drug testing is challenging in terms of consistent diagnostic criteria and lack of reliable biomarkers. Few randomized controlled trials (RCTs) are well-designed, with enough power to detect significant drug effects. Levodopa monotherapy can treat the parkinsonism in DLB, but it can cause agitation or visual hallucination worsening. Two Phase II/III RCTs of DLB patients recently reported a statistically significant improvement in motor function in those receiving zonisamide as an adjunctive treatment to levodopa. New biomarker strategies and validated outcome measures for DLB or prodromal DLB may enhance clinical trial design for the development of specific disease-modifying treatments.

Determination of levetiracetam in human plasma by online heart-cutting liquid chromatography: Application to therapeutic drug monitoring

Levetiracetam is an antiepileptic drug for the treatment of psychiatric patients. In this study, a selective, straightforward, and rapid online heart-cutting liquid chromatography method was developed for the therapeutic drug monitoring of levetiracetam. This method allows for the determination of levetiracetam in human plasma without complex sample preparation. The mobile phases consisted of 30 mM aq. orthophosphoric acid solution/methanol (70:30) at a flow rate of 1 mL/min for the first system and 10 mM aq. orthophosphoric acid solution/methanol (55:45) at a flow rate of 1 mL/min for the second system. The first separation was carried out on a GL Sciences Intersil ODS-3 column (4.6 mm × 150 mm, 3 µm) and the second separation was carried out on a Restek Ultra PFPP column (4.6 mm × 150 mm, 5 µm). The detection was carried out at 205 nm for both systems. The method was validated for selectivity and linearity, which were in the 6-60 µg/mL range. Intra- and interassay accuracies were <112.6%, and the intra- and interassay precisions were <6.4% for all quality control samples. The lower limit of quantitation was 6 µg/mL. The developed method was successfully applied for therapeutic drug monitoring of plasma samples from patients.

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.

Comparison of performance characteristics between high-performance liquid chromatography and latex agglutination turbidimetric immunoassay for therapeutic drug monitoring of zonisamide

Background

Recently, the Nanopia^® TDM Zonisamide reagent using the latex particle‐enhanced turbidimetric immunoassay (LTIA) method was developed. The aim of this study was to compare the differences in serum zonisamide (ZNS) concentrations quantified by the high‐performance liquid chromatography (HPLC) method and the LTIA method using a TBA‐25FR analyzer.

Methods

A total of 78 samples from 33 patients were quantified by both HPLC and LTIA methods. Deproteinization was used as pretreatment for the HPLC method. The ZNS concentrations quantified by two methods were compared.

Results

The HPLC method had intra‐ and inter‐day precision lower than 1.86% and 9.00%, and accuracy better than 2.44% and 6.33%, respectively. The LTIA method showed intra‐ and inter‐day precision lower than 2.50% and 5.20%, and accuracy better than 15.80% and 10.60%, respectively. The lower limits of quantification for the HPLC and LTIA methods were 1.0 and 5.0 µg/mL, respectively. The ZNS concentration quantified by the HPLC method correlated strongly with that by the LTIA method (r = 0.953, P < 0.001). A Bland‐Altman plot suggested no systematic error between ZNS concentrations quantified by HPLC and LTIA methods.

Conclusion

This study confirmed no differences between the concentrations quantified by the HPLC and LTIA methods at both high and low concentrations, demonstrating the confidence of measurement by the LTIA method.

Topiramate: Comprehensive profile

Topiramate, 2,3:4,5-di-O-isopropylidene-β-d-fructopyranose sulfamate, is a potent antiepileptic drug with a broad spectrum of activity. It is effective in both partial and generalized seizures. Topiramate was also found to have significant efficacy in migraine prevention with considerable reductions in the frequency of migraine headaches. The most common adverse events, which may accompany the use of topiramate, are paresthesia, fatigue, decreased appetite, nausea, diarrhea, weight decrease and taste perversion. The weight loss observed with the use of topiramate in obese, epileptic patients, afforded the approval of this drug as an anti-obesity medication. This action is thought to be based on the selective inhibition of mitochondrial carbonic anhydrase isoforms. This profile is prepared to discuss and explain physical characteristics, proprietary and nonproprietary names of topiramate. It also includes methods of preparation, thermal and spectral behavior and methods of analysis. Pharmacokinetics, metabolism, excretion and pharmacology together with its uses and applications are also discussed.

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.

Computer-aided design of magnetic molecularly imprinted polymer nanoparticles for solid-phase extraction and determination of levetiracetam in human plasma

Analytical methods should be accurate and specific to measure plasma drug concentration. Nevertheless, current sample preparation techniques suffer from limitations, including matrix interference and intensive sample preparation. In this study, a novel technique was proposed for the synthesis of a molecularly imprinted polymer (MIP) on magnetic Fe₃O₄ nanoparticles (NPs) with uniform core–shell structure. The Fe₃O₄@MIPs NPs were then applied to separate and enrich an antiepileptic drug, levetiracetam, from human plasma. A computational approach was developed to screen the functional monomers and polymerization solvents to provide a suitable design for the synthesized MIP. Different analysis techniques and re-binding experiments were performed to characterize the Fe₃O₄@MIP NPs, as well as to identify optimal conditions for the extraction process. Adsorption isotherms were best fitted to the Langmuir model and adsorption kinetics were modeled with pseudo-second-order kinetics. The Fe₃O₄@MIP NPs showed reasonable adsorption capacity and improved imprinting efficiency. A validated colorimetric assay was introduced as a comparable method to a validated HPLC assay for the quantitation of levetiracetam in plasma in the range of 10–80 μg mL⁻¹ after extraction. The results from the HPLC and colorimetric assays showed good precision (between 1.08% and 9.87%) and recoveries (between 94% and 106%) using the Fe₃O₄@MIP NPs. The limit of detection and limit of quantification were estimated to be 2.58 μg mL⁻¹ and 7.81 μg mL⁻¹, respectively for HPLC assay and 2.32 μg mL⁻¹ and 7.02 μg mL⁻¹, respectively for colorimetric assay. It is believed that synthesized Fe₃O₄@MIP NPs as a sample clean-up technique combined with the proposed assays can be used for determination of levetiracetam in plasma.

A novel molecularly imprinted polymer on Fe₃O₄ nanoparticles was applied to extract antiepileptic drug; levetiracetam from plasma for TDM purposes.

Levetiracetam Monotherapy in Children with Epilepsy: A Systematic Review

BACKGROUND

Levetiracetam, a second-generation anti-epileptic drug (AED) with a good efficacy and safety profile, is licensed as monotherapy for adults and children older than 16 years with focal seizures with or without secondary generalization. However, it is increasingly being used off-label in younger children.

OBJECTIVES

We critically reviewed the available evidence and discuss the present status of levetiracetam monotherapy in children 0-16 years old.

DATA SOURCES

We systematically searched the literature using PubMed, Web of Science and Embase up to August 2014 for articles on levetiracetam monotherapy in children. Keywords were levetiracetam, monotherapy and child*. The titles and abstracts of 532 articles were evaluated by AW, of which 480 were excluded. The full texts of the other 52 articles were assessed for relevance.

RESULTS

We covered one review, one opinion statement and 32 studies in this review, including four randomized controlled trials, ten open-label prospective studies, eight retrospective studies, and ten case reports. The formal evidence for levetiracetam monotherapy in children is minimal: it is potentially efficacious or effective as initial monotherapy in children with benign epilepsy with centrotemporal spikes. In all of the published studies, however, efficacy and tolerability of levetiracetam seemed to be good and comparable to other AEDs.

CONCLUSION

The data of 32 studies on levetiracetam monotherapy in children were insufficient to confirm that levetiracetam is effective as initial monotherapy for different types of seizures and/or epilepsy syndromes. There is still an urgent need for well designed trials to justify the widespread use of levetiracetam monotherapy in children of all ages.

A simple and accurate liquid chromatography-tandem mass spectrometry method for quantification of zonisamide in plasma and its application to a pharmacokinetic study

Zonisamide (ZNM) is an antiepileptic drug that is used as an adjunctive therapy in the treatment of adults with partial seizures. An LC-MS/MS method for quantification of ZNM in human and rabbit plasma using (2)H4,(15)N-Zonisamide as an internal standard (IS) has been developed and validated. The drug and IS were extracted by ether and analyzed on Symmetry(®) C18 column. Quantitation was achieved using ESI-interface employing MRM mode. The method was validated over the concentration range of 0.5-50μg/mL and 0.5-30μg/mL (r(2)>0.99) in human and rabbit plasma samples, respectively. Intra- and inter-run precision of ZNM assay in human and rabbit plasma samples ranged from 0.8 to 8.5% with accuracy (bias) varied from -11.3 to 14.4% indicating good precision and accuracy. Stability of ZNM in human and rabbit plasma samples at various conditions showed that the drug was stable under the studied conditions. Analytical recoveries of ZNM and IS from spiked human and rabbit plasma samples were in the range of 70.8-77.3% and 85.6-110.4%, respectively. Matrix effect study showed a lack of matrix effect on mass ions of ZNM and IS. The developed method was successfully applied for a pharmacokinetic study by measuring ZNM in rabbit plasma samples. Moreover, the method is routinely utilized for TDM of ZNM.

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.

Zonisamide: newer antiepileptic agent with multiple mechanisms of action

Zonisamide (Zonegran, Eisai, Inc.) is a broad spectrum antiepileptic drug indicated for use as adjunctive therapy in the treatment of partial seizures. Zonisamide has multiple mechanisms of action, which may explain widespread reports of its utility in focal epilepsy and generalized epilepsy, and for nonseizure disorders such as headache and neuropathic pain. Zonisamide has been available in Japan since 1989 and became available in the USA in 2002. The rights to this drug in North America and Europe were recently acquired by Eisai Co. A review of the chemical properties, pharmacokinetics, metabolism, potential mechanisms of action, efficacy in seizure and nonseizure disorders, and tolerability was therefore thought to be timely.

A simple assay for determination of levetiracetam in rat dried blood spots by LC-MS/MS

BACKGROUND

A simple LC-MS/MS method was developed and validated for the quantification of levetiracetam (LEV, Keppra®), a broad-spectrum antiepileptic drug (AED) in rat dried blood spots (DBS). LEV was simply extracted with methanol spiked with adenosine (ADE) as IS before LC-MS/MS analysis. The correlation between the DBS and plasma concentrations of LEV was also determined.

RESULTS

Linearity was from 0.067-60 µg/ml for LEV in DBS samples. The intra- and inter-day accuracy and precision of the assay met validation acceptance criteria. The developed assay was applied to monitor levetiracetam DBS levels in Sprague-Dawley rats after intravenous administration. DBS concentrations were well correlated to the plasma concentrations (R² = 0.9399), as fraction of LEV bound to blood cells remains very constant (0.466 ± 0.041) over a wide concentration range.

CONCLUSION

The study illustrated that DBS could be used as alternative matrix for monitoring LEV in preclinical studies.

Levetiracetam: Relative Bioavailability and Bioequivalence of a 10% Oral Solution (750 mg) and 750-mg Tablets

Levetiracetam, an antiepileptic drug, is used worldwide as an adjunctive treatment for partial-onset seizures. The availability of a new oral solution formulation would provide an additional treatment option for patients who have difficulty swallowing tablets. A phase I single-center, randomized, open-label, two-way crossover, single-dose study was conducted to confirm that a 10% oral solution of levetiracetam was bioequivalent to the 750-mg oral tablet and to characterize its pharmacokinetics. Each of 24 healthy subjects received a single oral 750-mg dose of the randomized levetiracetam formulation (7.5 mL of 10% solution or 750-mg tablet) on day 1 and a single oral dose of the alternate formulation on day 8. Serial blood samples were collected from 0 to 36 hours after each dose administration for determination of plasma levetiracetam concentrations. Pharmacokinetic parameters were calculated, and bioequivalence of the two formulations was evaluated. The mean levetiracetam plasma concentration-time curves and pharmacokinetic parameters essentially were identical for the oral 10% solution and tablet and consistent with previously reported levetiracetam pharmacokinetics. The 90% confidence limits of the geometric mean ratio of the two formulations for area under the plasma concentration-time curve from time 0 to infinity, area under the plasma concentration-time curve from time 0 to last measurable time point, and maximum plasma concentration were within the 80% to 125% range, demonstrating bioequivalence of the two formulations. Both levetiracetam formulations were well tolerated. The levetiracetam 10% oral solution is a bioequivalent, well-tolerated alternative to the tablet formulation in patients who have difficulty swallowing.

New developments in the treatment of partial-onset epilepsy

Although most people presenting with partial-onset seizures will achieve control with antiepileptic medication, a considerable minority will have difficult-to-treat epilepsy that is resistant to existing medication. Over the last few years, a large number of new antiepileptic drugs have been developed. Some of these have a novel mode of action. Many of the older antiepileptic drugs act through sodium channels or by enhancement of gamma amino butyric acid (GABA). Lamotrigine has sodium-channel blocking properties but also has other important modes of action, indicated by efficacy in treating not only partial-onset but also generalized seizures. Vigabatrin and tiagabine both increase GABA activity, by inhibiting GABA transaminase and limiting GABA reuptake, respectively. The main mode of action of gabapentin and pregabalin is not via GABA but through a selective inhibitory effect on voltage-gated calcium channels containing the α(2)δ-1 subunit. Levetiracetam inhibits the recycling of SV2A (synaptic vesicle protein 2A) neurotransmitter vesicles but also has other effects, including inhibition of voltage-dependent calcium channels. Some drugs, eg, felbamate, zonisamide, and topiramate, have multiple modes of action. In many cases, although the main mode of action may have been identified, other modes of action also play a role. Two recently developed antiepileptic drugs appear to have completely novel primary modes of action; retigabine (ezogabine) and perampanel act on the potassium channel and on AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptors, respectively. The hope is that antiepileptic drugs with a novel mode of action will be effective where previous drugs have failed and will not have unacceptable adverse effects. However, experience with these medications is too limited to allow any conclusions to be drawn at present.

Clinical pharmacology of topiramate in migraine prevention

INTRODUCTION

Migraine is a widespread disorder. Migraine patients experience worse health-related quality of life than the general population. The availability of effective and tolerable treatments for this disorder is an important medical need. This narrative review focuses on the clinical pharmacology of topiramate, an antiepileptic drug that was approved for the prophylaxis of migraine where it should act as a neuromodulator.

AREAS COVERED

A PubMed database search (from 2000 to 24 January 2011) and a review of the human studies published on topiramate and migraine was conducted.

EXPERT OPINION

Topiramate is an important option for the prophylaxis of migraine and is of proven efficacy and tolerability. It has also been studied in chronic migraine with encouraging results, even in patients with medication overuse. However, in migraine prevention its efficacy is comparable to the other first-line drugs and there are no published trials with a superiority design which can establish topiramate's role in the available therapeutic armamentarium.

A simple, rapid and specific method for measurement of topiramate in human plasma by LC-MS/MS employing automated solid-phase extraction techniques: Application for bioequivalence study

A rapid liquid chromatography coupled with ESI tandem mass spectrometry (LC-MS/MS) method was developed and validated for the quantification of topiramate in heparinized human plasma. The plasma samples were prepared by solid-phase extraction (SPE) method without drying and then reconstitution. Topiramate and the topiramate d-12 internal standard (IS) were chromatographed on a Betasil C18 column at a flow rate of 0.5 mL/min. The total run time was 1.80 min. An ESI interface with negative ion mode was selected for ionization of analyte and IS. The mass transition [M-H] ions used for detection were m/z 338.10→78.20 for topiramate, m/z 350.40→90.10 for IS. The method was linear in the concentration range of 10-4200 ng/mL with r≥0.9992. Recovery of topiramate and IS ranged from 78.20 to 87.74%. The validated method has been successfully used to analyze human plasma samples for application in 100 mg fasted and fed pharmacokinetic studies.

Topiramate-induced confusion following a single ingestion of 400 mg

BACKGROUND

Topiramate is an anticonvulsant medication commonly used for a variety of neurological disorders including migraine prophylaxis. Broadened use of topiramate has brought an increased awareness of toxicity from this medication, particularly central nervous system side effects and metabolic acidosis.

OBJECTIVE

We describe a case of topiramate toxicity occurring in a 22-year-old female following the ingestion of two 200 mg tablets, which she was prescribed for the treatment of migraines.

RESULTS

During her outpatient cardiology evaluation for suspected postural orthostatic tachycardia syndrome (POTS), the patient experienced flushing and anxiety. Upon transfer to our hospital she was tachycardic, hypertensive, and confused. Her autonomic symptoms were consistent with her prior episodes of autonomic instability, while the confusion was new. Admission laboratory values revealed a metabolic acidosis with a mildly elevated anion gap. A blood topiramate level returned a value of 8.4 mg/L 15 h after the ingestion. Her symptoms cleared within 24 h following admission.

CONCLUSION

Clinicians should consider topiramate toxicity in their differential diagnosis for patients with neurological diseases presenting with acute-onset confusion and metabolic acidosis.

Topiramate in the new generation of drugs: efficacy in the treatment of alcoholic patients

Predicated upon a neuropharmacological conceptual model, there is now solid clinical evidence to support the efficacy of topiramate for the treatment of alcohol dependence. Topiramate treatment can be initiated whilst the alcohol-dependent individual is still drinking - just when crisis intervention is most likely to be needed by a patient with or without his or her family asking the health practitioner for assistance. Because topiramate can be paired with a brief intervention, there is now the exciting possibility of treating most alcohol- dependent individuals in office-based practice or generic treatment settings. Topiramate's additional effects on other impulsedyscontrol disorders make it a particularly interesting compound for the treatment of other comorbid drug or psychiatric disorders. Additionally, future studies should explore whether topiramate can be combined with other putative therapeutic agents to increase its efficacy. One notable clinical challenge in the development of topiramate as a pharmacotherapy to treat alcohol dependence is the determination of the smallest dose that can result in efficacy, thereby achieving the optimum balance between therapeutic benefit and adverse event profile. Animal data do provide support for topiramate's general anti-drinking effects but also indicate that its mechanisms of action might rely on several complex pharmacobehavioral changes. Additional preclinical studies are needed to elucidate more clearly the basic mechanistic processes that underlie topiramate's efficacy as a treatment for alcohol dependence. Preclinical information that topiramate may have differential effects based on genetic vulnerability opens up the possibility of future methods to optimize treatment.

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.

The challenge of pain management in patients with myasthenia gravis

Myasthenia gravis (MG) is an autoimmune disorder of the neuromuscular junction. The complexity of the disease and its treatments make MG patients particularly susceptible to adverse effects of drugs. MG is not a painful condition; however, as pain management armamentarium includes drugs from diverse pharmacological groups and with potential for drug-drug interactions, managing pain in patients with MG can be challenging. The underlying disease and the concomitant medications of each patient must be considered and the analgesic treatment individualized. This review presents an update on the various aspects of pain pharmacotherapy in patients with MG, focusing primarily on medications used to treat chronic pain. Drugs discussed are opioids, nonsteroidal anti-inflammatory drugs, antidepressants, anticonvulsants, muscle relaxants, benzodiazepines, intravenous magnesium, and local anesthetics. Drug interactions with agents used for MG treatment (acethylcholinesterase inhibitors, corticosteroids, immunosuppressants) and plasmapheresis are discussed. The clinical usefulness and limitations of each of the drug classes and agents are described.

Possible removal of topiramate by continuous renal replacement therapy

BACKGROUND

Topiramate is primarily renally eliminated and requires dosage adjustment based upon renal function. While there is data to suggest drug removal during intermittent hemodialysis (IHD), little is known regarding its clearance and dosing during continuous renal replacement therapy (CRRT).

CASE DESCRIPTION

We describe a 59-year-old man with refractory status epilepticus who was started on continuous venovenous hemodiafiltration (CVVHDF) for acute renal failure while receiving topiramate with a series of serum concentrations to assess for removal during CVVHDF.

CONCLUSION

Our data suggest clinically important amounts of topiramate are removed by CRRT, and higher topiramate dosage may be needed for these patients instead of the current recommended 50% of normal dosage. Unfortunately, there is no antiepileptic drug dosing recommendation when used during CRRT due to the paucity of data. This case highlights a need for research evaluating the effect of CRRT on AED elimination in order to optimize therapy for seizure control.

[Current clinical evidence on topiramate pharmacokinetics]

Topiramate is biochemically classified as a fructopyranose sulphamate. Discovered as early as 1979, during middle 1980's it was approved in many countries for the treatment of epilepsies and migraine prevention. More recently, in the experimental stage, possible new indications have been disclosed: treatment of obesity, bipolar disorder, also cessation of smoking, neuropathic pain, cerebral pseudotumour, bulimia, periventricular leucomalatia in preterm infants and alcohol addiction. Most epileptologists consider it to be the first choice antiepileptic drug in severe pharmacoresistant epilepsies. A substantial corpus of evidence in paediatric population has been accumulated that confirms its efficiency in the treatment of generalised tonic-clonic seizures, Lenox-Gestaut syndrome, partial, absence and combined seizures. Having a unique monosaccharide chemical structure among other anticonvulsant drugs, characterizes it with special pharmacokinetic features. This substance exhibits a low interindividual variability in plasma levels and hence it features predictable pharmacokinetics. A steady state plasma concentration of topiramate increases linearly with higher dosages. Serum protein binding is approximately 15%, and biologic half-life in healthy volunteers is considered to range from 20 to 30 hours. Mean expected distribution volume rates from 0.55-0.8 l/kg, and accordingly, the drug shows a low and saturable binding capacity toward erythrocytes. It has not been present at the market for a sufficiently long time that would enable us to speak about a significant accumulation of data on its metabolism based on post-registration 4th stage clinical trials. For this purpose, we have done a literature review in order to summarise so far reported experience on topiramate pharmacokinetics in patients and healthy adults. Deeper understanding of its pharmacokinetic profile could enable a better technological design of the produced drug and the choice of the adequate route of its administration, and accordingly a more rational treatment of severe epilepsies resistant to other drugs.

Topiramate concentrations in neonates treated with prolonged whole body hypothermia for hypoxic ischemic encephalopathy

PURPOSE

Therapeutic hypothermia reduces mortality and neurologic impairment in neonates with hypoxic-ischemic encephalopathy. Topiramate exerts a neuroprotective effect in asphyxiated neonatal animal models. However, no studies have investigated the association of hypothermia and topiramate, because topiramate pharmacokinetics during hypothermia and the optimal administration schedule are unknown. The influence of hypothermia on topiramate pharmacokinetics was evaluated in asphyxiated neonates treated with prolonged whole-body hypothermia and topiramate.

METHODS

Thirteen term newborns were treated with mild or deep whole body hypothermia for 72 h; all received oral topiramate, 5 mg/kg once a day for the first 3 days of life, and seven had concomitant phenobarbital treatment. Topiramate concentrations were measured on serial dried blood spots.

RESULTS

Topiramate concentrations were within the reference range in 11 of 13 newborns, whereas concentrations exceeded the upper limit in 2 of 13, both newborns on deep hypothermia. Topiramate concentrations reached a virtual steady state in nine newborns, for whom pharmacokinetic parameters were calculated. Values of topiramate maximal and minimal concentration, half-life, average concentration, and area under the time-concentration curve resulted in considerably higher values than those reported in normothermic infants. With respect to normothermic infants, time of maximal concentration was mildly delayed and apparent total body clearance was lower, suggesting slower absorption and elimination. Pharmacokinetic parameters did not differ significantly between infants on deep versus mild hypothermia and in those on topiramate monotherapy versus add-on phenobarbital.

CONCLUSION

Most neonates on prolonged hypothermia treated with topiramate 5 mg/kg once a day exhibited drug concentrations within the reference range for the entire treatment duration.

Pharmacokinetics of topiramate during pregnancy

PURPOSE

To study the effects of pregnancy on plasma concentrations of topiramate (TPM).

METHODS

An established routine fluorescence polarization immunoassay (FPIA) method was used to determine TPM concentrations in 15 women with epilepsy treated with TPM during altogether 17 pregnancies.

RESULTS

In 10 pregnancies, where samples were available from all three trimesters, the mean TPM dose/concentration ratio (D/C-ratio) was significantly higher than outside pregnancy baseline value 37.3 L/day (+/-15.9), during the 2nd, 67.5L/day (+/-23.4), and the 3rd trimester, 65.1L/day (+/-30.4), but not during the 1st, 49.4 L/day (+/-29.4). Including seven additional pregnancies enrolled late with data only from the 3rd trimester, the mean D/C-ratio during the 3rd trimester was 67.4 L/day (+/-27.5) compared to baseline, 38.8L/day (+/-18.0), an average increase by 71.8%. There was a pronounced intra-individual variability in alterations in D/C-ratios during pregnancies.

CONCLUSIONS

Our data show a significant pregnancy-related increase in D/C-ratios of TPM suggesting that therapeutic drug monitoring might be of value.

Topiramate reduces excitability in the basolateral amygdala by selectively inhibiting GluK1 (GluR5) kainate receptors on interneurons and positively modulating GABAA receptors on principal neurons

Topiramate [2,3:4,5-bis-O-(1-methylethylidene)-beta-D-fructopyranose sulfamate] is a structurally novel antiepileptic drug that has broad efficacy in epilepsy, but the mechanisms underlying its therapeutic activity are not fully understood. We have found that topiramate selectively inhibits GluK1 (GluR5) kainate receptor-mediated excitatory postsynaptic responses in rat basolateral amygdala (BLA) principal neurons and protects against seizures induced by the GluK1 kainate receptor agonist (R,S)-2-amino-3-(3-hydroxy-5-tert-butylisoxazol-4-yl)propanoic acid (ATPA). Here, we demonstrate that topiramate also modulates inhibitory function in the BLA. Using whole-cell recordings in rat amygdala slices, we found that 0.3 to 10 microM topiramate 1) inhibited ATPA-evoked postsynaptic currents recorded from BLA interneurons; 2) suppressed ATPA-induced enhancement of spontaneous inhibitory postsynaptic currents (IPSCs) recorded from BLA pyramidal cells; and 3) blocked ATPA-induced suppression of evoked IPSCs, which is mediated by presynaptic GluK1 kainate receptors present on BLA interneurons. Topiramate (10 microM) had no effect on the AMPA [(R,S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid]-induced enhancement of spontaneous activity of BLA neurons. Thus, although topiramate inhibits GluK1 kainate receptor-mediated enhancement of interneuron firing, it promotes evoked GABA release, leading to a net inhibition of circuit excitability. In addition, we found that topiramate (0.3-10 microM) increased the amplitude of evoked, spontaneous, and miniature IPSCs in BLA pyramidal neurons, indicating an enhancement of postsynaptic GABA(A) receptor responses. Taken together with our previous findings, we conclude that topiramate protects against hyperexcitability in the BLA by suppressing the GluK1 kainate receptor-mediated excitation of principal neurons by glutamatergic afferents, blocking the suppression of GABA release from interneurons mediated by presynaptic GluK1 kainate receptors and directly enhancing GABA(A) receptor-mediated inhibitory currents.