Clinical pharmacokinetics of new antiepileptic drugs

Levetiracetam dosing in continuous renal replacement therapy: A systematic review and development of a novel pharmacokinetic model to optimise dosing in critically ill patients. Do recommended doses achieve therapeutic drug concentrations?

Aim

Levetiracetam is a widely used anti-epileptic in the critical care setting that is almost exclusively (>90%) renally excreted. The altered pharmacokinetics of levetiracetam have been widely studied in intermittent haemodialysis but the evidence and guidance on dosage in continuous renal replacement therapy is varied and poorly defined. Understanding this is critical as a significant number of critically unwell patients develop renal failure requiring continuous renal replacement therapy. The aim of this systematic review is to investigate the pharmacokinetics of levetiracetam in such patients and to understand the implications on dosing strategies.

Methods

A systematic review of the available literature from 2000 to November 2022 was conducted. Seven articles were identified for inclusion from 54 records. A novel hybrid model was developed to evaluate the quality of pharmacokinetic and haemofiltration data. This data was used to develop a one-compartment model that simulated dosing strategies in 10,000 patients based on an assumed steady state of 72 hr and target trough concentrations of 12-46 mcg/mL.

Results

From the seven articles included, pharmacokinetic data was retrieved for 24 individual patients. Total clearance was 3.49-4.63 L/hr (mean 3.55, S.D. 0.52). Elimination half-life was 5.66-12.88 hr (mean 9.41, S.D. 2.86). Volume of distribution was 0.45-0.73 L/kg. The proportion of total clearance attributable to continuous renal replacement therapy was 52%-73% (mean 54.7%, S.D. 13.5). Our simulations demonstrate that more than half of patients who received twice daily doses of 750 mg or greater without a loading dose achieved therapeutic drug concentrations. The time to achievement of therapeutic drug concentrations was greatly reduced by the addition of a 60 mg/kg loading dose (up to a maximum of 4.5 g). The use of a reduced loading dose or twice daily doses of 500 mg or less without loading were more likely to result in prolonged sub-therapeutic drug concentrations.

Conclusion

Levetiracetam clearance in haemofiltration is similar to healthy adults with normal renal function (GFR > 90 mL/min). The use of reduced doses due to renal failure in critically ill patients may result in sub-therapeutic drug concentrations in a high number of patients. A twice daily dosing of 750-1000 mg with an initial loading dose of 60 mg/kg should be considered in such patients alongside therapeutic drug monitoring.

Research Status, Synthesis and Clinical Application of Antiepileptic Drugs

According to the 2017 ILAE's official definition, epilepsy is a slow brain disease state characterized by recurrent episodes. Due to information released by ILAE in 2017, it can be divided into four types, including focal epilepsy, generalized epilepsy, combined generalized, and focal epilepsy, and unknown epilepsy. Since 1989, 24 new antiepileptic drugs have been approved to treat different types of epilepsy. Besides, there are a variety of antiepileptic medications under clinical monitoring. These novel antiepileptic drugs have plenty of advantages. Over the past 33 years, there have been many antiepileptic drugs on the mearket, but no one has been found that can completely cure epilepsy. In this paper, the mentioned drugs were classified according to their targets, and the essential information, and clinical studies of each drug were described. The structure-activity relationship of different chemical structures was summarized. This paper provides help for the follow-up research on epilepsy drugs.

A review of the pharmacology and clinical applications of levetiracetam in dogs and cats

OBJECTIVE

To review and summarize the pharmacology of the antiepileptic drug (AED), levetiracetam (LEV), and to discuss its clinical utility in dogs and cats.

DATA SOURCES

Veterinary and human peer-reviewed medical literature and the authors' clinical experience.

SUMMARY

LEV is an AED with mechanisms of action distinct from those of other AEDs. In people and small animals, LEV exhibits linear kinetics, excellent oral bioavailability, and minimal drug-drug interactions. Serious side effects are rarely reported in any species. LEV use is gaining favor for treating epilepsy in small animals and may have wider clinical applications in patients with portosystemic shunts, neuroglycopenia, and traumatic brain injury. In people, LEV may improve cognitive function in patients with dementia.

CONCLUSION

LEV is a well-tolerated AED with well-documented efficacy in human patients. Although its use is becoming more common in veterinary medicine, its role as a first-line monotherapy in small animal epileptics remains to be determined. This review of the human and animal literature regarding LEV describes its role in epileptic people and animals as well as in other disease states and provides recommendations for clinical usage.

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.

Bioequivalence and Safety of Levetiracetam Granules and Oral Solution: A Randomized, Single-Dose, 2-Period Crossover Study in Healthy Chinese Volunteers Under a Fasting Condition

The bioequivalence and safety of levetiracetam granules (test formulation) and oral solution (reference formulation) were evaluated in Chinese healthy volunteers under a fasting condition. A total of 24 subjects randomly received the test or reference formulation at the rate of 1:1. The alternative formulation was administered after a 7-day washout period. The blood samples were collected at designated time points. Liquid chromatography-tandem mass spectrometry was applied to determine the plasma concentrations of levetiracetam. Adverse events were monitored and recorded. The 90% CIs for the geometric mean ratios of maximum plasma concentration, area under the plasma concentration-time curve from time 0 to the last quantifiable concentration, and area under the plasma concentration-time curve from time 0 to infinity between test preparation and reference preparation were 95.5% to 110.7%, 100.2% to 105.3%, and 100.3% to 105.7%, respectively, all within an acceptable bioequivalence range of 80.00% 125.00%. Both test and reference preparations were well tolerated. The trial confirmed that a single dose of 500-mg levetiracetam granules was bioequivalent to oral solution under a fasting condition, and may serve as a new dosage form of levetiracetam for clinical practice.

Role of memantine in the prophylactic treatment of episodic migraine: A systematic review

OBJECTIVE

The purpose of this systematic review is to assess the efficacy and safety of memantine for the prophylactic treatment of episodic migraine.

BACKGROUND

Migraine is a prevalent chronic disease with significant costs to the health care system. Although various prophylactic treatment options are available, these medications have limitations based on efficacy, potential side effects, and patient preference. Memantine is an N-methyl-d-aspartate receptor antagonist used in dementia treatment that may have potential benefit for migraine prophylaxis.

METHODS

A systematic search of PubMed, Embase, and CENTRAL databases was conducted to identify relevant published studies through December 2020 using the search terms: migraine disorders, migraine, headache disorders, or headache and memantine. Studies selected for the systematic review included prospective, interventional designs and evaluated memantine for prophylaxis of migraine. Animal studies, case reports, abstracts, review articles, protocols without results, and studies not written in English were excluded. Data were extracted using a standardized systematic process and included author, publication date, study design, sample size, patient characteristics, treatment regimen, clinical efficacy outcomes, and adverse drug effects.

RESULTS

Four articles were identified for inclusion representing two prospective open-label studies and two randomized, double-blind trials, evaluating 183 patients on memantine overall. A reduction in number of migraine days and headache severity were shown in all four studies in the participants treated with memantine. The most common adverse effects included somnolence, sedation, and nausea, none of which were severe.

CONCLUSION

The studies in this review establish that memantine has the potential for use as a treatment option for episodic migraine. Additional long-term studies using an active comparator would be useful to further elucidate its role.

[Efficacy and safety of levetiracetam versus phenytoin as second-line drugs for the treatment of children with convulsive status epilepticus: a Meta analysis]

OBJECTIVE

To systematically evaluate the efficacy and safety of levetiracetam (LEV) versus phenytoin (PHT) as second-line drugs for the treatment of convulsive status epilepticus (CSE) in children.

METHODS

English and Chinese electronic databases were searched for the randomized controlled trials comparing the efficacy and safety of LEV and PHT as second-line drugs for the treatment of childhood CSE. RevMan 5.3 software was used for data analysis.

RESULTS

Seven studies with 1 434 children were included. The Meta analysis showed that compared with the PHT group, the LEV group achieved a significantly higher control rate of CSE (RR=1.12, 95%CI:1.00-1.24, P=0.05), but there was no significant difference between the two groups in the recurrence rate of epilepsy within 24 hours (RR=0.82, 95%CI:0.22-3.11, P=0.77) and the rate of further antiepileptic drug therapy (RR=0.97, 95%CI:0.64-1.45, P=0.87). There was no significant difference in the incidence rate of adverse events between the two groups (RR=0.77, 95%CI:0.55-1.09, P=0.15).

CONCLUSIONS

LEV has a better clinical effect than PHT in the treatment of children with CSE and does not increase the incidence rate of adverse events.

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.

LC-MS/MS Quantification of Tramadol and Gabapentin Utilizing Solid Phase Extraction

An accurate, highly sensitive, and precise method for quantitative analysis of tramadol (TMD) and gabapentin (GBP) by high performance liquid chromatography and tandem mass spectrometry in human plasma was proposed and validated successfully using venlafaxine and pregabalin as internal standards (ISTDs), respectively. An aliquot of 200 μL of plasma was mixed with internal standard dilution and extraction was performed by using solid phase extraction (SPE) technique. Peak resolution was achieved on Phenomenex PFP column (50×4.6 mm, 2.6 μm). The total analytical run time was 3.8 min. Both analytes were monitored using multiple reaction monitoring (MRM) scan and the mass spectrometer was operated in positive polarity mode. The method was validated for specificity, sensitivity, precision, accuracy, and other analytical parameters. The results found were satisfactory over the linear calibration range of 1-500 ng/mL and 10-6000 ng/mL for TMD and GBP, respectively. The developed method can be ready to use by scientific community for quantification of analytes in plasma samples from various clinical studies of different dose strengths.

Pharmacokinetics and Drug Interaction of Antiepileptic Drugs in Children and Adolescents

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

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Levetiracetam Pharmacokinetics in a Patient with Intracranial Hemorrhage Undergoing Continuous Veno-Venous Hemofiltration

Patient: Male, 78

Final Diagnosis: Right thalamic intraparenchymal hemorrhage with intraventricular extension

Symptoms: Altered mental status • left sided weakness

Medication: Levetiracetam

Clinical Procedure: Continuous renal replacement therapy

Specialty: Critical Care Medicine

Potential problems and recommendations regarding substitution of generic antiepileptic drugs: a systematic review of literature

Despite the availability of generic antiepileptic drugs (AEDs), still patients and neurologists hesitate to make a switch due to assorted reasons. The objectives of this review were to evaluate the risks associated with the generic substitution of AEDs. In this context, we also summarized the recommendations of various international societies to treat epileptic patients. We used a number of electronic databases to identify the relevant published studies which demonstrated the potential problems and recommendations regarding generic substitution of AEDs. Of 204 articles found initially, 153 were selected for additional review. Subsequently, 68 articles were finally selected. This review concluded that potential problems linked with the generic substitution of AEDs could be bioequivalence issues, failure of drug therapy, emergence of adverse events and increase in the frequency of seizures. The reasons could be the pharmacokinetics properties of AEDs and unique characteristics of some epilepsy patients. Consequently, the generic substitution of AEDs affects the successful treatment and quality of life of the patients. Various guidelines recommend the well-controlled epileptic patients to avoid switching from brand-to-generic products, generic-to-brand products or generic to some other generic products.

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.

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.

[Therapeutic drug monitoring of stiripentol]

Stiripentol is a third generation antiepileptic, marketed since 2007 under the name of Diacomit(®). It is indicated, always in combination, in the treatment of severe myoclonic epilepsy in infancy or Dravet syndrome. Its pharmacokinetics is not linear. It is a potent inhibitor of CYP3A4, 1A2 and 2C19 and increases the plasma concentrations of many other antiepileptic drugs. Without this being considered as a validated therapeutic range, the trough plasma concentrations at steady-state, corresponding to the usual doses are between 10 and 15 mg/L. The concentration-efficacy relationship is not established, but there is some evidence for a concentration-related toxicity. However, because of its non-linear kinetics, stiripentol should be a good candidate for therapeutic drug monitoring (TDM). Nonetheless, the current level of evidence for the advantage of TDM is "remains to be estimated".

Cyclic Voltammetric Investigation of Dopamine at Poly-(Gabapentin) Modified Carbon Paste Electrode

The poly (gabapentin) film was prepared on the surface of carbon paste electrode by electrochemical method using cyclic voltammetric technique. The poly (gabapentin) film-modified carbon paste electrode was calibrated with standard potassium ferrocyanide solution in 1 M KCl as a supporting electrolyte. The prepared poly (gabapentin) film-coated electrode exhibits excellent electrocatalytic activity towards the detection of dopamine at physiological pH. The scan rate effect was found to be diffusion-controlled electrode process. The concentration effect of dopamine was studied, and the redox peak potentials of dopamine were dependant on pH.

Zonisamide: review of pharmacology, clinical efficacy, tolerability, and safety

BACKGROUND

Zonisamide (ZNS), a sulphonamide derivative, is a new-generation anticonvulsant with multiple potential mechanisms that contribute to its antiepileptic efficacy and may also explain its as yet incompletely assessed utility for non-seizure disorders such as headaches, neuropathic pain, and weight loss.

OBJECTIVE

A review of the pharmacokinetics, pharmacodynamics, evidence for efficacy in different seizure types and non-seizure conditions, adverse effects, and tolerability of ZNS is presented.

METHODS

A review of all manuscripts published in the English literature on ZNS was performed in preparing this manuscript.

RESULTS/CONCLUSIONS

ZNS has a broad label for use in Japan, while the regulatory bodies in the USA and Europe have approved it for use only as an adjunctive therapy for partial seizures in adults. It has favorable pharmacokinetic characteristics, proven efficacy in seizure disorders, and is well tolerated in long-term use.

Development and application of a validated HPLC method for the determination of gabapentin and its major degradation impurity in drug products

A simple isocratic reversed-phase HPLC method for the determination of gabapentin and its major degradation impurity, 3,3-pentamethylene-4-butyrolactam, was developed and validated for use in the analysis of pharmaceutical tablets and capsules. Separation was achieved on a Brownlee Spheri-5 Cyano column using an acetonitrile-10 mM KH2PO4/10 mM K2HPO4 (pH 6.2) (8:92, v/v) mobile phase. The compounds were eluted isocratically at a flow rate of 1 mL/min. Both compounds were analyzed with UV detection at 210 nm. The method was validated according to USP Category I requirements for gabapentin and USP Category II for 3,3-pentamethylene-4-butyrolactam. The validation characteristics included accuracy, precision, linearity, range, specificity, limit of quantitation and robustness. Validation acceptance criteria were met in all cases. This method was used successfully for the quality assessment of four gabapentin drug products.

Pharmacokinetics and Drug Interactions with Zonisamide

Polypharmacy is a widely employed treatment strategy in epilepsy, particularly for individuals with poorly controlled seizures. Drug combinations should be carefully considered to minimize the potential for unfavorable interactions. Older-generation antiepileptic drugs (AEDs) are well known for their pharmacokinetic interaction potential, which generally results from alterations in the metabolism of concomitant drugs due to effects on the cytochrome P450 (CYP) and uridine glucuronyl transferase enzyme systems. Newer agents, such as zonisamide, are less likely to cause adverse drug interactions. A series of interaction studies has revealed zonisamide to be without effect on the steady-state pharmacokinetics of carbamazepine, phenytoin, sodium valproate, or lamotrigine. However, zonisamide is principally inactivate by CY3A4-dependent reduction. Consequently, carbamazepine, phenytoin, and phenobarbital all increase its clearance, an interaction that may necessitate a dosage increase, but which will also permit more rapid attainment of steady-state zonisamide concentrations. Otherwise, zonisamide is essentially devoid of clinically significant interactions with other AEDs, oral contraceptives and, indeed, all other classes of therapeutic agents investigated to date. As a result, it is reasonable to conclude that zonisamide has a favorable pharmacokinetic profile and that it may be a useful and uncomplicated agent when employed as adjunctive therapy in refractory epilepsy.

Validated LC-MS/MS method for quantification of gabapentin in human plasma: application to pharmacokinetic and bioequivalence studies in Korean volunteers

A sensitive validated liquid chromatography-tandem mass spectrometric method (LC-MS/MS) for gabapentin (GB) in human plasma has been developed and applied to pharmacokinetic (PK) and bioequivalence (BE) studies in human. In a randomized crossover design with a 1-week period, each subject received a 300 mg GB capsule. The procedure involves a simple protein precipitation with acetonitrile and separated by LC with a Gemini C(18) column using acetonitrile-10 mm ammonium acetate (20:80, v/v, pH 3.2) as mobile phase. The GB and internal standard [(S)-(+)-alpha-aminocyclohexanepropionic acid hydrate] were analyzed using an LC-API 2000 MS/MS in multiple reaction monitoring mode. The ionization was optimized using ESI(+) and selectivity was achieved using MS/MS analysis, m/z 172.0 --> 154.0 and m/z 172.0 --> 126.0 for GB and IS, respectively. The assay exhibited good linearity over a working range of 20-5000 ng/mL for GB in human plasma with a lower limit of quantitation of 20 ng/mL. No endogenous compounds were found to interfere with the analysis. The accuracy and precision were shown for concentrations over the standard ranges. This method was successfully applied for the PK and BE studies by analysis of blood samples taken up to 36 h after an oral dose of 300 mg of GB in 24 healthy volunteers.

Rapid quantification of gabapentin in human plasma by liquid chromatography/tandem mass spectrometry

A simple, sensitive and rapid liquid chromatography/tandem mass spectrometry (LC-MS/MS) method was developed and validated for the quantification of gabapentin, a new antiepileptic drug, in human plasma using its structural analogue, 1,1-cyclohexane diacetic acid monoamide (CAM) as internal standard. The method involved a simple protein precipitation by means of acetonitrile followed by a rapid isocratic elution with 10mM ammonium formate buffer/acetonitrile (20/80, v/v, pH 3.0) on Waters Symmetry C(18 reversed phase chromatographic column and analyzed by mass spectrometry in the multiple reaction monitoring mode. The precursor to product ion transitions of m/z 172-->154 and m/z 200-->182 were used to measure the analyte and the IS, respectively. The assay exhibited a linear dynamic range of 40-10000 ng/mL for gabapentin in human plasma. The limit of detection and lower limit of quantification in human plasma were 10 and 40 ng/mL, respectively. Acceptable precision and accuracy were obtained for concentrations over the standard curve ranges. A run time of 2 min for each sample made it possible to analyze a throughput of more than 400 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies.

Antiepileptic drugs and liver disease

Antiepileptic drugs (AEDs) are no longer restricted to the treatment of epilepsy. These are widely used in a broad spectrum of psychiatric and neurological disorders. Liver plays a major role in the metabolism of a majority of these drugs. Hepatotoxicity is rare, but a real concern when initiating therapy. Likewise, liver disease can adversely affect the biotransformation of some of these drugs. This manuscript addresses the significance of elevated liver enzymes associated with AED use, the role of therapeutic drug monitoring, pharmacokinetics during liver disease and potential risk of hepatotoxicity.

Challenges and opportunities in the application of pharmacogenetics to antiepileptic drug therapy

The recent surge of interest in pharmacogenetics has provoked considerable thought regarding its relevance to antiepileptic drug (AED) therapy. Initial studies have focused on genes whose products play a putatively important role in AED pharmacology, particularly drug transporter proteins, drug metabolizing enzymes and ion channel subunits. However, there is a lack of good correspondence between results from different laboratories, and more recent findings are awaiting attempts at confirmation. Thus, there are currently no AED treatment guidelines that are informed by pharmacogenetic data. In order to begin to have clinical impact, standards specific to the conduct of future AED studies must be established. Of particular importance are the need for accurate epilepsy classification, appropriate AED selection and clear and objective assessment outcome measures. In addition, general standards for analysis and interpretation of genetic association data must be better codified and applied consistently across studies. Finally, extensive clinical research networks must be formulated and large numbers of well characterized patients must be recruited. Further development of these critical factors will optimize chances for overcoming current challenges posed by AED pharmacogenetic research and ultimately allow the realization of improved, more rational therapeutic strategies.

Levetiracetam in the Treatment of Idiopathic Generalized Epilepsies

Since its introduction into clinical practice in 1999, levetiracetam, the S enantiomer of piracetam, has rapidly found a secure place, initially in the therapy of partial onset seizures and subsequently in the treatment of idiopathic generalized epilepsies (IGE). It has many of the properties of an "ideal" antiepileptic drug, including rapid absorption, linear pharmokinetics, and sparse drug interactions. Tolerabiliy is generally excellent in both adults and children, although tiredness is a common dose-limiting adverse effect. Occasionally the drug can precipitate behavioral abnormalities, especially in patients with learning disability. There is a wide safety margin in overdose. In common with most antiepileptic drugs its mode of action remains uncertain. Levetiracetam binds to a specific site in the brain, influences intracellular calcium currents and reverses negative allosteric modulators of GABA- and glycine-gated currents in vitro. Its effectiveness has been demonstrated in animal models of epilepsy and in clinical trials of partial onset and IGE. Treatment of IGEs may be straightforward, with many patients demonstrating an excellent and robust response to valproate monotherapy. However, there remains a significant minority of patients for whom valproate is unsuitable, including those who experience unacceptable adverse effects (e.g., weight gain or hair loss) and women of childbearing age in whom the teratogenic potential of valproate is unacceptable. Therapeutic response to lamotrigine in this group is often disappointing, and many clinicians now are turning to the choice of levetiracetam. Efficacy in generalized tonic-clonic seizures and myoclonus is usually apparent and some patients experience improvement in typical absences. Experience of combinations of levetiracetam with other antiepileptic drugs is limited in IGE and the responses are largely anecdotal. In our hands, patients with refractory IGEs may respond to combinations of levetiracetam with valproate, lamotrigine, and phenobarbital, and adverse effects when they occur are usually limited to tiredness. Levetiracetam does not interact with the oral contraceptive pill, simplifying treatment in women of childbearing age. Although animal data look encouraging, questions over levetiracetam's teratogenic potential and overall safety in pregnancy will remain for many years to come.

Development of capillary zone electrophoresis-electrospray ionization-mass spectrometry for the determination of lamotrigine in human plasma

A method of coupling capillary zone electrophoresis (CZE) with electrospray ionization-mass spectrometry (ESI-MS) detection has been developed for monitoring an antiepileptic drug, lamotrigine (LTG) in human plasma. The CZE-MS was developed in three stages: (i) CZE separation and ESI-MS detection of LTG and tyramine (TRM, internal standard) were simultaneously optimized by studying the influence of CZE background electrolyte (BGE) pH, BGE ionic strength, and nebulizer pressure of the MS sprayer; (ii) sheath liquid parameters, such as pH, ionic strength, organic modifier content, and flow rate of the sheath liquid, were systematically varied under optimum CZE-MS conditions developed in the first stage; (iii) MS sprayer chamber parameters (drying gas temperature and drying gas flow rate) were varied for the best MS detection of LTG. The developed assay was finally applied for the determination of LTG in plasma samples. The linear range of LTG in plasma sample assay was between 0.1-5.0 microg/mL with a limit of detection as low as 0.05 microg/mL and run time less than 6 min. Finally, the concentration-time profile of LTG in human plasma sample was found to correlate well when CZE-ESI-MS was compared to a more established method of high-performance liquid chromatography with ultraviolet detection.