Pharmacokinetics and Drug Interactions with Zonisamide

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.

Zonisamide oral suspension as adjunctive therapy for treating partial seizures in adults and in pediatric patients aged 16 years and older with epilepsy

INTRODUCTION

Zonisamide (ZNS), is an antiseizure medication (ASM) approved by the US FDA and the European Medicines Agency (EMA) for focal-onset seizures. An oral suspension formulation has recently been introduced to improve administration for specific patient populations, particularly those with swallowing difficulties.

AREAS COVERED

This article explores the new ZNS oral suspension, evaluating its pharmacokinetic benefits, impact on patient care, and adherence. Bioavailability studies confirm that the oral suspension is bioequivalent to ZNS capsules, though no additional clinical trials in epilepsy patients have been conducted. This review presents and discusses the oral suspension's benefits, such as ease of administration for those with swallowing difficulties and flexible dosing, while also addressing potential drawbacks, including dosing accuracy and stability issues.

EXPERT OPINION

The ZNS oral suspension allows additional flexibility for epilepsy management, particularly for patients unable to swallow capsules. Its bioavailability and specific formulation may improve adherence and seizure control.

The effect of oral zonisamide treatment on serum phenobarbital concentrations in epileptic dogs

Zonisamide is used in dogs for the treatment of epileptic seizures. It is predominantly metabolised by CYP450 hepatic enzymes. When used concurrently with phenobarbital (PB), zonisamide clearance is increased and its elimination half-life decreases. However, the effect that zonisamide may have on serum PB concentrations in dogs has not been previously described. Eight dogs diagnosed with idiopathic epilepsy and two dogs with structural epilepsy commenced zonisamide at 8.0 mg/kg/12 h [7.4-10 mg/kg/12 h] following an increase in the frequency of epileptic seizures. Nine dogs were receiving PB every 12 h (4.2 mg/kg/12 h [3.8-6 mg/kg/12 h]), and one dog was receiving PB every 8 h (6 mg/kg/8 h). Following the addition of zonisamide and despite no increase in PB dosage, an increase in phenobarbital serum PB concentration was observed in 9 out of 10 dogs in subsequent measurements. In five dogs, phenobarbital serum concentrations were raised to concentrations higher than the reported hepatotoxic concentrations (trough>35 mg/L). This required a reduction in daily doses of PB. This case series suggests that zonisamide affects the metabolism of PB and causes an increase in PB serum concentrations over time.

Zonisamide: A Comprehensive, Updated Review for the Clinician

Purpose of Review

Zonisamide (ZNS) was first approved in the United States in 2000 for the adjunctive treatment of patients aged 16 years or older with partial (focal) seizures. Although ZNS has been proven to treat multiple seizure types, it has been largely underutilized in US clinical practice.

Recent Findings

Published literature demonstrated that antiseizure medications (ASMs) acting on Na+ and Ca2+ channels may add beneficial effects in many seizure types by reducing seizure frequency and leading to overall improvements. In addition, effects of ZNS may lead to clinical improvements in Parkinson disease, alcohol and sleep disorders, pain, and migraine. ZNS is available in multiple formulations and is a safe and effective, broad spectrum ASM.

Summary

The purpose of this review was to provide an update to what is known about the efficacy of ZNS and where it shows benefits in the treatment of patients with epilepsy and other CNS disorders through its many unique mechanisms of action.

Bioequivalence of Different Formulations of Zonisamide Oral Suspensions: A Short Review

To satisfy the needs of pediatric and other patients with focal onset seizures who cannot swallow solid dosage forms of zonisamide, an oral liquid form of this drug is necessary in clinical practice. Although there are two oral suspensions of zonisamide with marketing authorization (MA), there are issues of availability and high cost which limit their use and inspire extemporaneous compounding. Extemporaneously compounded oral suspensions of zonisamide are prepared according to different formulas and vary in stability; therefore it is essential to test this characteristic. Bioequivalence of extemporaneously compounded oral suspensions has never been tested, and the efficacy and safety of zonisamide oral suspensions have generally not been demonstrated in clinical trials. As a narrow therapeutic window drug, zonisamide requires precision in dosing, which could be achieved only with dosage forms with established bioavailability, efficacy, and safety. In order to avoid underdosing and toxicity with zonisamide oral suspensions and utilize their full therapeutic potential, it is necessary to perform bioequivalence studies with each variation of extemporaneously compounded oral suspension and also clinical trials with both commercial and extemporaneous oral suspensions of zonisamide.

Optimizing Therapeutic Drug Monitoring in Pregnant Women: A Critical Literature Review

BACKGROUND

More than 90% of pregnant women take at least one drug during pregnancy. Drug dose adjustments during pregnancy are sometimes necessary due to various pregnancy-induced physiological alterations frequently associated with lower plasma concentrations. However, the clinical relevance or benefits of therapeutic drug monitoring (TDM) in pregnant women have not been specifically studied. Clinical pharmacokinetic studies in pregnant women are incredibly challenging for many reasons. Despite this, regulatory agencies have made efforts to encourage the inclusion of this population in clinical trials to achieve more information on the pharmacotherapy of pregnant women. This review aims to provide support for TDM recommendations and dose adjustments in pregnant women.

METHODS

The search was conducted after a predetermined strategy on PubMed and Scopus databases using the MeSH term "pregnancy" alongside other terms such as "Pregnancy and dose adjustment," "Pregnancy and therapeutic drug monitoring," "Pregnancy and PBPK," "Pregnancy and pharmacokinetics," and "Pregnancy and physiological changes."

RESULTS

The main information on TDM in pregnant women is available for antiepileptics, antipsychotics, antidepressants, antibiotics, antimalarials, and oncologic and immunosuppressive drugs.

CONCLUSIONS

More data are needed to support informed benefit-risk decision making for the administration of drugs to pregnant women. TDM and/or pharmacokinetic studies could ensure that pregnant women receive an adequate dosage of an active drug. Mechanistic modeling approaches potentially could increase our knowledge about the pharmacotherapy of this special population, and they could be used to better design dosage regimens.

Management of anti-seizure medications in lactating women with epilepsy

Epilepsy is a common neurological disease. At present, there are about 70 million epilepsy patients in the world, half of them are women, and 30-40% of women with epilepsy are of childbearing potential. Patients with epilepsy who are of childbearing potential face more challenges, such as seizures caused by hormonal fluctuations and the risk of adverse effects on the mother and baby from taking anti-seizure medications (ASMs). Breast milk is one of the best gifts that a mother can give her baby, and breastfeeding can bring more benefits to the baby. Compared with healthy people, people with epilepsy have more concerns about breastfeeding because they are worried that ASMs in their milk will affect the growth and development of the baby, and they are always faced with the dilemma of whether to breastfeed after childbirth. Regarding, whether women with epilepsy can breastfeed while taking ASMs, and whether breastfeeding will adversely affect the baby is still an important topic of concern for patients and doctors. This article reviews the existing research on breastfeeding-related issues in women with epilepsy to guide clinical practice, and improve the breastfeeding compliance of women with epilepsy.

Phytochemicals That Interfere With Drug Metabolism and Transport, Modifying Plasma Concentration in Humans and Animals

Phytochemicals (Pch) present in fruits, vegetables and other foods, are known to inhibit or induce drug metabolism and transport. An exhaustive search was performed in five databases covering from 2000 to 2021. Twenty-one compounds from plants were found to modulate CYP3A and/or P-gp activities and modified the pharmacokinetics and the therapeutic effect of 27 different drugs. Flavonols, flavanones, flavones, stilbenes, diferuloylmethanes, tannins, protoalkaloids, flavans, hyperforin and terpenes, reduce plasma concentration of cyclosporine, simvastatin, celiprolol, midazolam, saquinavir, buspirone, everolimus, nadolol, tamoxifen, alprazolam, verapamil, quazepam, digoxin, fexofenadine, theophylline, indinavir, clopidogrel. Anthocyanins, flavonols, flavones, flavanones, flavonoid glycosides, stilbenes, diferuloylmethanes, catechin, hyperforin, alkaloids, terpenes, tannins and protoalkaloids increase of plasma concentration of buspirone, losartan, diltiazem, felodipine, midazolam, cyclosporine, triazolam, verapamil, carbamazepine, diltiazem, aripiprazole, tamoxifen, doxorubicin, paclitaxel, nicardipine. Interactions between Pchs and drugs affect the gene expression and enzymatic activity of CYP3A and P-gp transporter, which has an impact on their bioavailability; such that co-administration of drugs with food, beverages and food supplements can cause a subtherapeutic effect or overdose. Therefore, it is important for the clinician to consider these interactions to obtain a better therapeutic effect.

Hearing loss drug discovery and medicinal chemistry: Current status, challenges, and opportunities

Hearing loss is a severe high unmet need condition affecting more than 1.5 billion people globally. There are no licensed medicines for the prevention, treatment or restoration of hearing. Prosthetic devices, such as hearing aids and cochlear implants, do not restore natural hearing and users struggle with speech in the presence of background noise. Hearing loss drug discovery is immature, and small molecule approaches include repurposing existing drugs, combination therapeutics, late-stage discovery optimisation of known chemotypes for identified molecular targets of interest, phenotypic tissue screening and high-throughput cell-based screening. Hearing loss drug discovery requires the integration of specialist therapeutic area biology and otology clinical expertise. Small molecule drug discovery projects in the global clinical portfolio for hearing loss are here collated and reviewed. An overview is provided of human hearing, inner ear anatomy, inner ear delivery, types of hearing loss and hearing measurement. Small molecule experimental drugs in clinical development for hearing loss are reviewed, including their underpinning biology, discovery strategy and activities, medicinal chemistry, calculated physicochemical properties, pharmacokinetics and clinical trial status. SwissADME BOILED-Egg permeability modelling is applied to the molecules reviewed, and these results are considered. Non-small molecule hearing loss assets in clinical development are briefly noted in this review. Future opportunities in hearing loss drug discovery for human genomics and targeted protein degradation are highlighted.

Reactive metabolites of the anticonvulsant drugs and approaches to minimize the adverse drug reaction

Several generations of antiepileptic drugs (AEDs) are available in the market for the treatment of seizures, but these are amalgamated with acute to chronic side effects. The most common side effects of AEDs are dose-related, but some are idiosyncratic adverse drug reactions (ADRs) that transpire due to the formation of reactive metabolite (RM) after the bioactivation process. Because of the adverse reactions patients usually discontinue the medication in between the treatment. The AEDs such as valproic acid, lamotrigine, phenytoin etc., can be categorized under such types because they form the RM which may prevail with life-threatening adverse effects or immune-mediated reactions. Hepatotoxicity, teratogenicity, cutaneous hypersensitivity, dizziness, addiction, serum sickness reaction, renal calculi, metabolic acidosis are associated with the metabolites of drugs such as arene oxide, N-desmethyldiazepam, 2-(1-hydroxyethyl)-2-methylsuccinimide, 2-(sulphamoy1acetyl)-phenol, E-2-en-VPA and 4-en-VPA and carbamazepine-10,11-epoxide, etc. The major toxicities are associated with the moieties that are either capable of forming RM or the functional groups may itself be too reactive prior to the metabolism. These functional groups or fragment structures are typically known as structural alerts or toxicophores. Therefore, minimizing the bioactivation potential of lead structures in the early phases of drug discovery by a modification to low-risk drug molecules is a priority for the pharmaceutical companies. Additionally, excellent potency and pharmacokinetic (PK) behaviour help in ensuring that appropriate (low dose) candidate drugs progress into the development phase. The current review discusses about RMs in the anticonvulsant drugs along with their mechanism vis-a-vis research efforts that have been taken to minimize the toxic effects of AEDs therapy.

Ion-Channel Antiepileptic Drugs: An Analytical Perspective on the Therapeutic Drug Monitoring (TDM) of Ezogabine, Lacosamide, and Zonisamide

The term seizures includes a wide array of different disorders with variable etiology, which currently represent one of the most important classes of neurological illnesses. As a consequence, many different antiepileptic drugs (AEDs) are currently available, exploiting different activity mechanisms and providing different levels of performance in terms of selectivity, safety, and efficacy. AEDs are currently among the psychoactive drugs most frequently involved in therapeutic drug monitoring (TDM) practices. Thus, the plasma levels of AEDs and their metabolites are monitored and correlated to administered doses, therapeutic efficacy, side effects, and toxic effects. As for any analytical endeavour, the quality of plasma concentration data is only as good as the analytical method allows. In this review, the main techniques and methods are described, suitable for the TDM of three AEDs belonging to the class of ion channel agents: ezogabine (or retigabine), lacosamide, and zonisamide. In addition to this analytical overview, data are provided, pertaining to two of the most important use cases for the TDM of antiepileptics: drug–drug interactions and neuroprotection activity studies. This review contains 146 references.

Cost-Effectiveness of Zonisamide Versus Levetiracetam in Newly Diagnosed Focal Onset Epilepsy in Serbia

OBJECTIVES

When choosing initial therapy for epilepsy, the decision should be supported by studies that include both treatment outcome and costs. This is especially important for developing countries with restricted budgets because such circumstances are also characterized by higher epilepsy prevalence rates. The aim of this study was to compare cost-utility of zonisamide (ZNS) and levetiracetam (LEV) in patients with newly diagnosed focal-onset epilepsy in the Republic of Serbia.

METHODS

A 5-state, 3-month-cycle Markov model was created to compare ZNS and LEV. The model assumed that patients whose seizures were not controlled by treatment with either ZNS or LEV would be continued on carbamazepine in controlled-release form in the second cycle and would then be treated with a pregabalin add-on if still not adequately controlled. The perspective of the Serbian Republic Health Insurance Fund was chosen, and the time horizon was 15 years. Model results were obtained after Monte Carlo microsimulation of a sample with 1000 virtual patients. Both multiple one-way and probabilistic sensitivity analyses were performed.

RESULTS

After base-case analysis, LEV was dominated by ZNS because the net monetary benefit was positive (16 940.78 ± 22 572.26 Serbian dinars; €144.09 ± €191.99) and the incremental cost-effectiveness ratio was below the willingness-to-pay threshold of 3 Serbian gross domestic products per capita per quality-adjusted life-year gained. Multiple one-way and probabilistic sensitivity analyses confirmed the results of the base-case simulation.

CONCLUSIONS

ZNS has a more beneficial cost-effectiveness ratio than LEV for the treatment of newly diagnosed focal epilepsy in Serbian milieu.

Therapeutic Drug Monitoring of Antiepileptic Drugs in Women with Epilepsy Before, During, and After Pregnancy

During pregnancy, the pharmacokinetics of an antiepileptic drug is altered because of changes in the clearance capacity and volume of distribution. These changes may have consequences for the frequency of seizures during pregnancy and fetal exposure to antiepileptic drugs. In 2009, a review was published providing guidance for the dosing and therapeutic drug monitoring of antiepileptic drugs during pregnancy. Since that review, new drugs have been licensed and new information about existing drugs has been published. With this review, we aim to provide an updated narrative overview of changes in the pharmacokinetics of antiepileptic drugs in women during pregnancy. In addition, we aim to formulate advice for dose modification and therapeutic drug monitoring of antiepileptic drugs. We searched PubMed and the available literature on the pharmacokinetic changes of antiepileptic drugs and seizure frequency during pregnancy published between January 2007 and September 2018. During pregnancy, an increase in clearance and a decrease in the concentrations of lamotrigine, levetiracetam, oxcarbazepine's active metabolite licarbazepine, topiramate, and zonisamide were observed. Carbamazepine clearance remains unchanged during pregnancy. There is inadequate or no evidence for changes in the clearance or concentrations of clobazam and its active metabolite N-desmethylclobazam, gabapentin, lacosamide, perampanel, and valproate. Postpartum elimination rates of lamotrigine, levetiracetam, and licarbazepine resumed to pre-pregnancy values within the first few weeks after pregnancy. We advise monitoring of antiepileptic drug trough concentrations twice before pregnancy. This is the reference concentration. We also advise to consider dose adjustments guided by therapeutic drug monitoring during pregnancy if the antiepileptic drug concentration decreases 15-25% from the pre-pregnancy reference concentration, in the presence of risk factors for convulsions. If the antiepileptic drug concentration changes more than 25% compared with the reference concentration, dose adjustment is advised. Monitoring of levetiracetam, licarbazepine, lamotrigine, and topiramate is recommended during and after pregnancy. Monitoring of clobazam, N-desmethylclobazam, gabapentin, lacosamide, perampanel, and zonisamide during and after pregnancy should be considered. Because of the risk of teratogenic effects, valproate should be avoided during pregnancy. If that is impossible, monitoring of both total and unbound valproate is recommended. More research is needed on the large number of unclear pregnancy-related effects on the pharmacokinetics of antiepileptic drugs.

The role of sex, age and genetic polymorphisms of CYP enzymes on the pharmacokinetics of anticholinergic drugs

There is evidence that use of drugs with anticholinergic properties increases the risk of cognitive impairment, and increased exposure to these drugs potentiates this risk. Anticholinergic drugs are commonly used even with associated risk of adverse events. Aging, sex, and genetic polymorphisms of cytochrome P450 (CYP) enzymes are associated with alterations in pharmacokinetic processes, which increase drug exposure and may further increase the risk of adverse drug events. Due to the increasing burden of cognitive impairment in our aging population and the future of personalized medicine, the objective of this review was to provide a critical clinical perspective on age, sex, and CYP genetic polymorphisms and their role in the metabolism and exposure to anticholinergic drugs. Age-related changes that may increase anticholinergic drug exposure include pseudocapillarization of liver sinusoidal endothelial cells, an approximate 3.5% decline in CYP content for each decade of life, and a reduction in kidney function. Sex-related differences that may be influenced by anticholinergic drug exposure include women having delayed gastric and colonic emptying, higher gastric pH, reduced catechol-O-methyl transferase activity, reduced glucuronidation, and reduced renal clearance and men having larger stomachs which may affect medication absorption. The overlay of poor metabolism phenotypes for CYP2D6 and CYP2C19 may further modify anticholinergic drug exposure in a significant proportion of the population. These factors help explain findings of clinical trials that show older adults and specifically older women achieve higher plasma concentrations of anticholinergic drugs and that poor metabolizers of CYP2D6 experience increased drug exposure. Despite this knowledge neither age, sex nor CYP phenotype are routinely considered when making decisions about the use or dosing of anticholinergic medications. Future study of anticholinergic medication needs to account for age, sex and CYP polymorphisms so that we may better approach personalized medicine for optimal outcomes and avoidance of medication-related cognitive impairment.

Zonisamide for the Treatment of Parkinson Disease: A Current Update

Zonisamide has been used as an add-on treatment in order to overcome the deficiencies of the general therapies currently used to resolve the motor complications and non-motor symptoms of Parkinson disease. Various trials have been designed to investigate the mechanism of action and treatment effects of zonisamide in this condition. Most clinical trials of zonisamide in Parkinson disease were from Japan. The vast majority of studies used changes in the Unified Parkinson’s Disease Rating Scale (UPDRS) scores and daily “OFF” time as primary endpoints. Based on adequate randomized controlled trials, zonisamide is considered a safe and efficacious add-on treatment in Parkinson disease. The most convincing proof is available for a dosage of 25–50 mg, which was shown to lead to a significant reduction in the UPDRS III score and daily “OFF” time, without increasing disabling dyskinesia. Furthermore, zonisamide may play a beneficial role in improving non-motor symptoms in PD, including impulsive–compulsive disorder, rapid eye movement sleep behavior disorder, and dementia. Among the various mechanisms reported, inhibition of monoamine oxidase-B, blocking of T-type calcium channels, modulation of the levodopa–dopamine metabolism, modulation of receptor expression, and neuroprotection are the most often cited. The mechanisms underlying neuroprotection, including modulation of dopamine turnover, induction of neurotrophic factor expression, inhibition of oxidative stress and apoptosis, inhibition of neuroinflammation, modulation of synaptic transmission, and modulation of gene expression, have been most extensively studied. This review focuses on structure, pharmacokinetics, mechanisms, therapeutic effectiveness, and safety and tolerability of zonisamide in patients with Parkinson disease.

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.

Effects of zonisamide monotherapy on bone health in drug-naive epileptic patients

OBJECTIVE

Alteration of bone strength is an adverse effect of antiepileptic drug treatment. We investigated the effects of zonisamide (ZNS) monotherapy on bone mineral density (BMD) and biomarkers of bone metabolism after 13 months of treatment in drug-naive epileptic patients.

METHODS

Fifty-nine patients with new onset drug-naive epilepsy were enrolled (29 women, 30 men; mean age = 31.5 ± 11.5 years). The BMD and T scores were measured at the lumbar spine and femoral neck by using dual-energy X-ray absorptiometry. Biomarkers specific for bone metabolism (bone-specific alkaline phosphatase, parathyroid hormone, osteocalcin, insulinlike growth factor-1, C-telopeptide, and vitamin D3 levels) were measured before and after long-term ZNS monotherapy. Analysis of covariance (ANCOVA) was used to estimate BMD and biomarkers of bone metabolism before and after ZNS therapy. Age, sex, treatment duration, and ZNS dosage were included as covariates for adjustment in the ANCOVA model. Furthermore, subgroup analyses were performed for each sex, and the effect size was calculated.

RESULTS

After 13 months of ZNS treatment, the BMD and T scores at the lumbar spine (L1-L4 level) and femoral neck were not significantly different. Moreover, the biochemical markers showed no significant differences after ZNS monotherapy. Women showed significantly decreased baseline BMD at the femoral neck compared to men (P = .026), although the mean age and body mass index were not significantly different between the sexes. No significant changes in BMD or biomarkers of bone metabolism were seen in either sex after 13 months of ZNS treatment.

SIGNIFICANCE

The results suggest that long-term ZNS monotherapy does not affect bone health in drug-naive patients with epilepsy negatively.

Pre-Clinical Assessment of the Nose-to-Brain Delivery of Zonisamide After Intranasal Administration

PURPOSE

Zonisamide clinical indications are expanding beyond the classic treatment of epileptic seizures to Parkinson's disease and other neurodegenerative diseases. However, the systemic safety profile of zonisamide may compromise its use as a first-line drug in any clinical condition. Since zonisamide is marketed as oral formulations, the present study aimed at exploring the potential of the intranasal route to centrally administer zonisamide, evaluating the systemic bioavailability of zonisamide and comparing its brain, lung and kidney pharmacokinetics after intranasal, oral and intravenous administrations.

METHODS

In vitro cell studies demonstrated that zonisamide and proposed thermoreversible gels did not affect the viability of RPMI 2650 or Calu-3 cells. Thereafter, male CD-1 mice were randomly administered with zonisamide by oral (80 mg/kg), intranasal or intravenous (16.7 mg/kg) route. At predefined time points, animals were sacrificed and plasma and tissues were collected to quantify zonisamide and describe its pharmacokinetics.

RESULTS

Intranasal route revealed a low absolute bioavailability (54.95%) but the highest value of the ratio between the area under the curve (AUC) between brain and plasma, suggesting lower systemic adverse events and non-inferior effects in central nervous system comparatively to intravenous and oral routes. Furthermore, drug targeting efficiency and direct transport percentage into the brain were 149.54% and 33.13%, respectively, corroborating that a significant fraction of zonisamide suffers direct nose-to-brain transport. Lung and kidney exposures obtained after intranasal administration were lower than those observed after intravenous injection.

CONCLUSIONS

This pre-clinical investigation demonstrates a direct nose-to-brain delivery of zonisamide, which may be a promising strategy for the treatment of central diseases.

The number and kind of antiepileptics affect propofol dose requirement for anesthesia: observational study

The propofol dose requirement and the emergence time are affected by antiepileptic use. The effects on anesthesia of the number and kind of antiepileptic agents have not been reported. We investigated the relationship between the kind and number of antiepileptic agents and the propofol dose requirement for anesthesia and emergence time in intravenous general anesthesia for dental treatment for patients with neurological disorders. We studied 247 patients with neurological disorders who underwent dental treatment under intravenous general anesthesia. Patients were categorized according to the number of antiepileptics (none, single agent, two kinds, and three or more kinds of antiepileptics) and the kind of antiepileptic (carbamazepine, valproate, phenobarbital, phenytoin, zonisamide, clobazam, or topiramate) being received. The propofol dose requirement for anesthesia, emergence time, and predicted blood propofol concentration at emergence were evaluated. Patients on three or more kinds of antiepileptics had significantly lower propofol dose requirement (reduction in 25%, compare with no use) and predicted blood propofol concentration at emergence (reduction in 41%) and significantly longer emergence time (extension in 50%) (P < 0.05). Valproate and clobazam reduced the propofol dose (valproate 9% and clobazam 19%) and predicted blood propofol concentration at emergence (valproate 18% and clobazam 33%), while phenobarbital increased these parameters (30% and 125%) (P < 0.05). The number and kind of antiepileptics effects propofol dose requirement. In particular, valproate and clobazam reduce the propofol dose requirement, while phenobarbital increases this.Clinical trial registration UMIN No. UMIN000014179.

Aldehyde oxidase and its role as a drug metabolizing enzyme

Aldehyde oxidase (AO) is a cytosolic enzyme that belongs to the family of structurally related molybdoflavoproteins like xanthine oxidase (XO). The enzyme is characterized by broad substrate specificity and marked species differences. It catalyzes the oxidation of aromatic and aliphatic aldehydes and various heteroaromatic rings as well as reduction of several functional groups. The references to AO and its role in metabolism date back to the 1950s, but the importance of this enzyme in the metabolism of drugs has emerged in the past fifteen years. Several reviews on the role of AO in drug metabolism have been published in the past decade indicative of the growing interest in the enzyme and its influence in drug metabolism. Here, we present a comprehensive monograph of AO as a drug metabolizing enzyme with emphasis on marketed drugs as well as other xenobiotics, as substrates and inhibitors. Although the number of drugs that are primarily metabolized by AO are few, the impact of AO on drug development has been extensive. We also discuss the effect of AO on the systemic exposure and clearance these clinical candidates. The review provides a comprehensive analysis of drug discovery compounds involving AO with the focus on developmental candidates that were reported in the past five years with regards to pharmacokinetics and toxicity. While there is only one known report of AO-mediated clinically relevant drug-drug interaction (DDI), a detailed description of inhibitors and inducers of AO known to date has been presented here and the potential risks associated with DDI. The increasing recognition of the importance of AO has led to significant progress in predicting the site of AO-mediated metabolism using computational methods. Additionally, marked species difference in expression of AO makes it is difficult to predict human clearance with high confidence. The progress made towards developing in vivo, in vitro and in silico approaches for predicting AO metabolism and estimating human clearance of compounds that are metabolized by AO have also been discussed.

Antiepileptic drug therapy in the elderly: a clinical pharmacological review

Seizure disorder is the third most common neurological disorder in the elderly after stroke and dementia. With the increasing geriatric population, the situation of clinicians seeing more and more elderly epilepsy patients is very likely. Not only is the diagnosis of epilepsy tedious in the elderly, its management raises many challenging issues for the treating physicians. Altered physiology, age-related decline in organ function, and plasma protein binding and altered pharmacodynamics make the elderly patients with seizure disorder a difficult group to treat. This is further complicated by the presence of comorbidities and polypharmacy which increase the chances of drug interactions. The adverse effects that might be tolerated well in younger populations may be disastrous for the aged. Although the newer antiepileptic drugs are found to have a favorable safety profile, there is relative scarcity of randomized-controlled trials involving older and newer antiepileptics in the geriatric population. This review tries to compile the available literature on management of epilepsy in the elderly population including evidence of safety and efficacy of newer and older antiepileptics with special reference to the 'geriatric giants'. It also deals with the interactions between antiepileptic medications and other commonly prescribed drugs in the elderly such as anti-hypertensives and antiischemic agents. The recommended guidelines of various international bodies are also analyzed from the perspective of elderly with seizure disorder.

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.

Pharmacometabolomics applied to zonisamide pharmacokinetic parameter prediction

INTRODUCTION

Zonisamide is a new-generation anticonvulsant antiepileptic drug metabolized primarily in the liver, with subsequent elimination via the renal route.

OBJECTIVES

Our objective was to evaluate the utility of pharmacometabolomics in the detection of zonisamide metabolites that could be related to its disposition and therefore, to its efficacy and toxicity.

METHODS

This study was nested to a bioequivalence clinical trial with 28 healthy volunteers. Each participant received a single dose of zonisamide on two separate occasions (period 1 and period 2), with a washout period between them. Blood samples of zonisamide were obtained from all patients at baseline for each period, before volunteers were administered any medication, for metabolomics analysis.

RESULTS

After a Lasso regression was applied, age, height, branched-chain amino acids, steroids, triacylglycerols, diacyl glycerophosphoethanolamine, glycerophospholipids susceptible to methylation, phosphatidylcholines with 20:4 FA (arachidonic acid) and cholesterol ester and lysophosphatidylcholine were obtained in both periods.

CONCLUSION

To our knowledge, this is the only research study to date that has attempted to link basal metabolomic status with pharmacokinetic parameters of zonisamide.

Could Adult European Pharmacoresistant Epilepsy Patients Be Treated With Higher Doses of Zonisamide?

OBJECTIVE

To examine the clinical effect (efficacy and tolerability) of high doses of zonisamide (ZNS) (>500 mg/d) in adult patients with pharmacoresistant epilepsy.

METHODS

Between 2006 and 2013, all epileptic outpatients treated with high doses of ZNS were selected. Safety and efficacy were assessed based on patient and caregiver reports. Serum levels of ZNS and other concomitant antiepileptic drugs were evaluated if available.

RESULTS

Nine patients (5 female): 8 focal/1 generalized pharmacoresistant epilepsy. Mean age: 34 years. Most frequent seizure type: complex partial seizures; other seizure types: generalized tonic-clonic, tonic, myoclonia. Zonisamide in polytherapy in all (100%), administered in tritherapy in 3 (33%) of 9 patients; mean dose: 633 (600-700) mg/d; efficacy (>50% seizure reduction) was observed in 5 (55%) of 9 patients. Five of 9 patients are still taking high doses of ZNS (more than 1 year). Adverse events were observed in 3 (37%) of 8 patients. Good tolerance to high doses of other antiepileptic drugs had been observed in 6 (66%) of 9 patients. Plasma levels of ZNS were only available in 2 patients; both were in the therapeutic range (34.95, 30.91) (10-40 mg/L).

CONCLUSIONS

High doses of ZNS are effective and safe in pharmacoresistant epileptic patients. Therapeutic drug monitoring of ZNS may be considered at therapeutic failure.

Effect of carbamazepine or phenytoin therapy on blood level of intravenously administered midazolam: a prospective cohort study

Dental treatment of intellectually disabled patients is frequently performed under general anesthesia or sedation. Many of these patients have epilepsy and are medicated with antiepileptic drugs (AEDs). Carbamazepine (CBZ) and phenytoin (PHT) are known to promote the metabolism of midazolam, and the blood levels of midazolam in patients medicated with CBZ or PHT may be different from those in healthy individuals. In this study, we clarified the influences of CBZ and PHT on the blood level of intravenously administered midazolam in patients medicated with CBZ or PHT. The subjects were divided into the following groups: not medicated with AEDs (control group), medicated with only CBZ or PHT (mono CBZ/PHT group), and medicated with CBZ or PHT or both and other AEDs (poly CBZ/PHT group). General anesthesia was achieved using midazolam, propofol, and remifentanil, and then the blood midazolam level was measured at 10, 30, and 60 min after intravenous midazolam administration. According to the results, the blood midazolam level was significantly lower in the mono and poly CBZ/PHT groups than in the control group. This finding suggests that intravenously administered midazolam may have a weaker effect in patients medicated with CBZ or PHT.

Zonisamide: Review of Recent Clinical Evidence for Treatment of Epilepsy

Zonisamide is an orally administered antiepileptic drug that was first approved for clinical use in Japan in 1989. Since then, it has been licensed in Korea for a broad spectrum of epilepsies in adults and children, and in the USA for adjunctive therapy of adults with partial seizures, and in Europe for monotherapy of adults with newly diagnosed partial seizures and adjunctive therapy of adults and adolescents and children aged ≥6 years with partial seizures with or without secondary generalization. Zonisamide is a benzisoxazole derivative with a unique chemical structure, predictable dose-dependent pharmacokinetics, and multiple complementary mechanisms of action. Treatment with zonisamide is well tolerated and is not known to be associated with clinically significant drug-drug interactions, including with oral contraceptives or other antiepileptic drugs. There have been >2 million patient-years of experience with zonisamide for treatment of epilepsy, and this drug has International League Against Epilepsy level A evidence for efficacy/effectiveness as initial monotherapy for adults with partial-onset seizures. This review presents the evidence for zonisamide across the spectrum of epilepsy, with emphasis on real-world clinical practice and special populations of patients (children, elderly patients, and women of childbearing age) who are likely to be treated in daily clinical practice.

The safety and long-term efficacy of zonisamide as adjunctive therapy for focal epilepsy

Epilepsy is a chronic disease which affects 1% of the population worldwide. As treatment is required for many years or decades, the long-term efficacy and tolerability of antiepileptic drugs are particularly important. Zonisamide (ZNS) is a second-generation antiepileptic drug with a unique structure and multiple mechanisms of action. Here, recently published long-term outcomes of patient cohorts with focal epilepsy undergoing ZNS treatment are discussed. Whereas ZNS monotherapy maintains similar seizure control efficacy to carbamazepine after 2 years of treatment, seizure-free rates are low in pharmacoresistant patients undergoing late adjunctive therapy. In preselected patient populations derived from double-blind studies, long-term seizure reduction and responder rates support sustained ZNS efficacy, good adherence and long-term retention. Adverse effects include somnolence and weight decrease, but data suggest that long-term treatment with ZNS is safe with only rare newly occurring adverse effects, and good long-term tolerability also regarding mood, behavior, cognition and bone maturation.

Zonisamide in the management of epilepsy in the elderly

Zonisamide (ZNS), a second-generation antiepileptic drug, indicated as add-on treatment of focal epilepsy, has been recently approved as monotherapy for the treatment of partial seizures in adults affected by newly diagnosed epilepsy in Europe. Evidence on the efficacy and tolerability of antiepileptic drugs in the elderly is still lacking as these patients are frequently excluded from clinical trials. Here, a comprehensive overview of available data regarding the use of ZNS in the treatment of epilepsy in elderly people is provided. In a pooled analysis conducted in patients aged ≥65 years, no new/unexpected safety findings have emerged. Few data from uncontrolled investigations suggest that ZNS may be effective and well tolerated when administered as monotherapy or adjunctive antiepileptic treatment in the elderly. However, evidence from these observational studies is less than satisfactory, and randomized controlled trials focused on these patients are still needed.

Use of Antiepileptic Drugs in Patients with Chronic Kidney Disease and End Stage Renal Disease

Epilepsy is a disorder with an approximate worldwide prevalence of 1%. Due to complexities of metabolism, protein-binding, renal elimination, and other pharmacokinetic parameters, the dosing of antiepileptic drugs (AEDs) in patients with chronic kidney disease (CKD) or end stage renal disease (ESRD) deserves special attention. This is a review of the most commonly prescribed AEDs with special focus on their indication, pharmacokinetics, and unique considerations for use in patients with CKD and ESRD. A review of their renal toxicities is also included.

Pharmacokinetic of antiepileptic drugs in patients with hepatic or renal impairment

Many factors influence choice of antiepileptic drugs (AEDs), including efficacy of the drug for the indication (epilepsy, neuropathic pain, affective disorder, migraine), tolerability, and toxicity. The first-generation AEDs and some newer AEDs are predominately eliminated by hepatic metabolism. Other recent AEDs are eliminated by renal excretion of unchanged drug or a combination of hepatic metabolism and renal excretion. The effect of renal and hepatic disease on the dosing will depend on the fraction of the AED eliminated by hepatic and/or renal excretion, the metabolic isozymes involved, as well as the extent of protein binding, if therapeutic drug monitoring is used. For drugs that are eliminated by renal excretion, methods of estimating creatinine clearance can be used to determine dose adjustments. For drugs eliminated by hepatic metabolism, there are no specific markers of liver function that can be used to provide guidance in dosage adjustments. Based on studies with probe drugs, the hepatic metabolic enzymes are differentially affected depending on the cause and severity of hepatic disease, which can aid in predicting dose adjustment when clinical data are not available. Several AEDs are also associated with laboratory markers of mild hepatic dysfunction and, rarely, more severe hepatic injury. In contrast, the risk of renal injury from AEDs is generally low. In general, co-morbid hepatic or renal diseases influence the decision for the selection of an AED. For some patients dosing changes to their existing AEDs may be appropriate. For others, a change to another AED may be a better option.

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.

Update on once-daily zonisamide monotherapy in partial seizures

Zonisamide is an antiepileptic drug that is structurally different from other antiepileptic agents. Its long half-life, once-daily dosing, lack of induction of hepatic enzymes, and broad spectrum of action makes it a suitable candidate for monotherapy. It has been approved as monotherapy for partial onset epilepsy in Japan and South Korea for more than a decade, and was recently approved as monotherapy in Europe. In the USA, it is only approved by the US Food and Drug Administration for adjunctive treatment of partial onset epilepsy. In this paper, we briefly review the literature on zonisamide monotherapy in partial onset epilepsy with regard to its efficacy, safety, tolerability, and long-term side effects, including a recent noninferiority trial in comparison with extended-release carbamazepine. While European regulatory agencies use noninferiority trials for approval of monotherapy, such a trial design does not meet the current regulatory requirements for approval as monotherapy in the USA.

What are the arguments for and against rational therapy for epilepsy?

Although more than a dozen new anti-seizure drugs (ASDs) have entered the market since 1993, a substantial proportion of patients (~30 %) remain refractory to current treatments. Thus, a concerted effort to identify and develop new therapies that will help these patients continues. Until this effort succeeds, it is reasonable to re-assess the use of currently available therapies and to consider how these therapies might be utilized in a more efficacious manner. This applies to the selection of monotherapies in newly-diagnosed epilepsy, but perhaps, more importantly, to the choice of combination treatments in otherwise drug-refractory epilepsy. Rational polytherapy is a concept that is predicated on the combination of drugs with complementary mechanisms of action (MoAs) that work synergistically to maximize efficacy and minimize the potential for adverse events. Furthermore, rational polytherapy requires a detailed understanding of the MoA subclasses amongst available ASDs and an appreciation of the empirical evidence that supports the use of specific combinations. The majority of ASDs can be loosely categorized into those that target neurotransmission and network hyperexcitability, modulate intrinsic neuronal properties through ion channels, or possess broad-spectrum efficacy as a result of multiple mechanisms. Within each of these categories, there are discrete pharmacological profiles that differentiate individual ASDs. This chapter will consider how knowledge of MoA can help guide therapy in a rational manner, both in the selection of monotherapies for specific seizure types and syndromes, but also in the choice of drug combinations for patients whose epilepsy is not optimally controlled with a single ASD.

Impact of pregnancy on zonisamide pharmacokinetics in rabbits

Pregnancy is associated with various physiological changes which may lead to significant alterations in the pharmacokinetics of many drugs. The present study was aimed to investigate the potential effects of pregnancy on the pharmacokinetic profile of zonisamide (ZNM) in the rabbit. Seven female rabbits were used in this study. The pregnant and nonpregnant rabbits received ZNM orally at a dose of 10 mg/kg and blood samples were collected from the animals just before receiving the drug and then serially for up to 24 h. The plasma samples were analyzed using tandem mass spectrometric method. Following a single oral dose of ZNM to the rabbits, the mean values of ZNM plasma concentrations at different times were consistently low in pregnant compared to nonpregnant rabbits. The mean values of ZNM's Cmax and AUC0-∞ were significantly (P < 0.05) decreased, whereas the CL/F exhibited substantial increase (P < 0.05) in pregnant compared to nonpregnant rabbits. Tmax, t1/2abs, t1/2el, MRT, and Vd/F showed no significant differences between the two groups. The present study demonstrates that pregnancy decreased ZNM plasma concentrations in rabbits and that the decrease could be due to decreased extent of gastrointestinal absorption, induced hepatic metabolism, or enhanced renal elimination of the drug.

Safe Treatment of Seizures in the Setting of HIV/AIDS

OPINION STATEMENT

HIV(+) patients are at increased risk for developing seizures due to the vulnerability of the central nervous system to HIV-associated diseases, immune dysfunction, and metabolic disturbances. In patients with acute seizures, standard protocols still apply with urgent seizure cessation being the priority. Management of the person with established epilepsy who contracts HIV is challenging, but the decision to initiate chronic antiepileptic drug (AED) therapy in an HIV(+) patient is also difficult. Chronic treatment guidelines emphasize the interactions between AEDs and antiretroviral (ARV) medications, but provide no explicit advice regarding when to initiate an AED, what medication to select, and/or the duration of treatment. Epidemiologic data regarding seizure recurrence risk in HIV(+) individuals is not available. The risk of further seizures likely depends upon the underlying etiology for the seizure(s) and patients' immune status and may be increased by the use of efavirenz (an ARV). The issues for consideration include AED-ARV interactions, organ dysfunction, seizure type, and drug side effects, which may worsen or be confused with symptoms of HIV and/or epilepsy. Co-administration of enzyme inducing (EI)-AEDs and ARVs can result in virological failure, breakthrough seizure activity, AED toxicity, and/or ARV toxicity. Where available, the AED of choice in HIV(+) patients is levetiracetam due to its broad spectrum activity, ease of use, minimal drug interactions, and favorable side effect profile. Lacosamide, gabapentin, and pregabalin are also favored choices in patients with partial onset seizures and/or those failing levetiracetam. Where newer AEDs are not available, valproic acid may be the treatment of choice in terms of an AED, which will not cause enzyme induction-associated ARV failure, but its side effect profile causes other obvious problems. In resource-limited settings (RLS) where only EI-AEDs are available, there are no good treatment options and further pressure needs to be placed upon policymakers to address this care gap and public health threat.

Profile of once-daily zonisamide as monotherapy for treatment of partial seizures in adults

Epilepsy is one of the most common neurologic disorders, affecting about 50 million people around the world. It is recognized that around 50% of patients with newly diagnosed epilepsy become seizure-free with the first drug treatment, so the choice of first antiepileptic drug is crucial. This paper provides a comprehensive overview of zonisamide as monotherapy for partial seizures, with special attention to the possibility of a once-daily regimen. The available data suggest that zonisamide is an effective and well tolerated option as monotherapy. Once-daily dosing is indicated, considering the long plasma half-life and linear pharmacokinetics of the drug. Zonisamide 300 mg was shown to be noninferior to carbamazepine 600 mg in terms of efficacy and safety, but even lower doses may be effective. Finally, the broad spectrum of efficacy in different seizure types, the low drug interaction potential, and the possibility of weight loss make zonisamide a preferred option in many epilepsy practices. Further data on monotherapy, especially in special populations, such as women of childbearing potential, are needed.

Rapid and sensitive high performance liquid chromatographic determination of zonisamide in human serum application to a pharmacokinetic study

An accurate and very rapid method for determination of zonisamide an antiepileptic drug, in human serum is described. The analytical procedure involves liquid-liquid extraction of the analyte and an internal standard (vanillin) from human serum by ethyl acetate as extracting solvent. Chromatographic separation was achieved using a monolithic C18 analytical column and a mixture of 0.05 M phosphate buffer containing triethylamine (1 ml/l; pH 2.7) and methanol (83:17 v/v) was used as the mobile phase. The detection wavelength was set at 240 nm. The calibration curve was linear over a concentration range of 0.015-6.4 μg/ml of zonisamide in human serum. The total run time of analysis was 3.5 min and the lower limits of detection and quantification were 0.005 and 0.015 μg/ml, respectively. The method validation was carried out in terms of specificity, sensitivity, linearity, precision, accuracy and stability. The validated method was applied in a randomised crossover bioequivalence study of two different zonisamide preparations in 24 healthy volunteers, and the assay was sensitive enough to measure drug levels up to 8 days following a single dose administration of zonisamide.

Second-generation antiepileptic drugs and pregnancy: a guide for clinicians

When treating pregnant women with antiepileptic drugs (AEDs), clinicians have to balance potential fetal adverse effects against the risks of uncontrolled maternal disease. Only recently have emerging scientic data provided a rational basis for treatment decisions considering both aspects. The focus of research is currently moving from the first to the second AED generation. Lamotrigine is relatively well studied, and data on other novel AEDs, such as levetiracetam, oxcarbazepine, topiramate, zonisamide, gabapentin and pregabalin, are in progress. Safety issues appear to be favorable for lamotrigine, and preliminary results are also promising for levetiracetam and oxcarbazepine. Drugs metabolized by uridine-diphospate glucuronosyl transferase or excreted unchanged by the kidneys are particularly susceptible to increased body clearance during pregnancy. Lamotrigine is subject to both mechanisms, and therapeutic serum levels may sometimes be difficult to maintain. The authors review the recommendations and clinical research on modern AED treatment during pregnancy, highlighting current experience with second-generation drugs.

Zonisamide: its pharmacology, efficacy and safety in clinical trials

Zonisamide is a benzisoxazole derivative, chemically unrelated to other antiepileptic drugs, that appears to have multiple mechanisms of action, including inhibition of Na(+) channels and reduction of T-type Ca(2+) currents. It is currently licensed in Europe and the USA for adjunctive treatment of partial seizures in adults, and in Europe as monotherapy for treatment of partial seizures in adults with newly diagnosed epilepsy. Zonisamide displays predictable, dose-dependent pharmacokinetics and has a half-life of ~60 h, allowing once- or twice-daily administration. It has a low potential for interactions with other medications, including oral contraceptives. The clinical efficacy of adjunctive zonisamide therapy has been established in four pivotal, phase III, randomized, double-blind, placebo-controlled trials, which together included approximately 850 patients, aged 12-77 years, with refractory partial epilepsy. In all four trials, zonisamide 300-600 mg/day resulted in significant reductions in median total seizure rates vs placebo, and zonisamide was generally well tolerated; the most frequently reported adverse events being somnolence, dizziness and anorexia/weight loss. Subanalysis of the primary European trial indicated that zonisamide was effective when administered as first-line adjunctive treatment, and a long-term extension to the same trial demonstrated that the efficacy and safety/tolerability of adjunctive zonisamide was sustained for up to 36 months. Once-daily monotherapy with zonisamide (200-500 mg/day) has been shown to be non-inferior to, and as well tolerated as, twice-daily monotherapy with controlled-release carbamazepine (400-1200 mg/day) in adults with newly diagnosed partial epilepsy. Zonisamide has also been shown to have favourable long-term retention rates, an important indication of its overall effectiveness.

Short-term efficacy and safety of zonisamide as adjunctive treatment for refractory partial seizures: a multicenter open-label single-arm trial in Korean patients

OBJECTIVE

To evaluate the efficacy and safety of adjunctive zonisamide (ZNS) therapy in Korean adults with uncontrolled partial epilepsy.

METHODS

Study patients had an average of at least one seizure per 4-week (averaged over a 12-week historical baseline) despite the use of one to three antiepileptic drugs. The starting dose of ZNS was 100mg/day, and was increased to 200mg/day after 2weeks. During the 12-week maintenance period, the dose of ZNS was adjusted to 200-400mg/day based on the physicians' discretion. The global evaluation scale (GES) and quality of life (QOLIE-31) were also evaluated.

RESULTS

A total of 121 patients were enrolled, of which 88 patients completed the study. The median percent reduction in weekly seizure frequency over the treatment period was 59.0%. The ≥50% and ≥75% responder rates were 57.3% and 38.5%, respectively. Seizure freedom over the treatment period was observed in 25 patients, but seizure freedom throughout the 16-week treatment period was attained in only 16 patients. On investigator's GES, 84 patients were considered improved, with 33 patients showing marked improvement. In QOLIE-31 scale, seizure worry improved significantly but emotional well-being deteriorated. Treatment-emergent adverse events (AEs) were reported in 80 patients. The most common AEs were dizziness (28.1%), somnolence (24.0%), anorexia (18.2%), headache (14.0%), nausea (13.2%), and weight loss (10.7%). Twenty-two patients discontinued the trial due to drug-related AEs.

CONCLUSIONS

Our results suggest that adjunctive ZNS therapy for the treatment of refractory partial epilepsy, though efficacious, is associated with significant tolerability problems.