Development of new antiepileptic drugs: challenges, incentives, and recent advances

Utilization of antiepileptic drugs in Hong Kong children

This study investigated the prescribing patterns of antiepileptic drugs, especially the uptake of newer drugs, among children and adolescents in Hong Kong. Data were retrieved from the Clinical Data Analysis and Reporting System. Children aged 0-19 years who received at least one prescription of anticonvulsants were selected. The study period extended from April 1, 2005 to March 31, 2009. The overall prevalence of anticonvulsants prescribing was 2.23/1000 children in 2005. A slight but steady decline in anticonvulsants prevalence was observed throughout the study period. Valproic acid was the most frequently prescribed drug, followed by carbamazepine and benzodiazepine derivatives. The use of newer anticonvulsants rose significantly, by 26.9%. The use of valproic acid remained unchanged, whereas the use of carbamazepine declined by 20%. Among newer drugs, the use of levetiracetam increased fourfold, and that of oxcarbazepine increased 15-fold. In the youngest age group, phenobarbital was the second most frequently used drug. A significant increase in lamotrigine prescriptions was not observed among adolescents. The persistent increase in using newer antiepileptic drugs implies not only an increase in drug expenditure. It also reflects the need to assess cost-effectiveness in terms of long-term outcomes, quality of life, and health economic outcomes.

Synthesis and anticonvulsant activity of 1-(2-(8-(benzyloxy)quinolin-2-yl)-1-butyrylcyclopropyl)-3-substituted urea derivatives

In the present study on the development of new anticonvulsants, 16 new1-(2-(8-(benzyloxy)quinolin-2-yl)-1-butyrylcyclopropyl)-3-substituted urea derivatives were synthesized and tested for anticonvulsant activity using the maximal electroshock seizure, subcutaneous pentylenetetrazole screens, which are the most widely employed seizure models for early identification of candidate anticonvulsants. Their neurotoxicity was determined by applying the rotorod test. Three compounds 7a, 7e, and 7m showed promising anticonvulsant activities in both models employed for anticonvulsant evaluation. The most active compound 7e showed the maximal electroshock seizure-induced seizures with ED(50) value of 14.3 mg/kg and TD(50) value of 434 mg/kg after intraperitoneal injection to mice, which provided compound 7e with a protective index (TD(50) /ED(50) ) of 30.3 in the maximal electroshock seizure test.

Identification of new epilepsy treatments: issues in preclinical methodology

Preclinical research has facilitated the discovery of valuable drugs for the symptomatic treatment of epilepsy. Yet, despite these therapies, seizures are not adequately controlled in a third of all affected individuals, and comorbidities still impose a major burden on quality of life. The introduction of multiple new therapies into clinical use over the past two decades has done little to change this. There is an urgent demand to address the unmet clinical needs for: (1) new symptomatic antiseizure treatments for drug-resistant seizures with improved efficacy/tolerability profiles, (2) disease-modifying treatments that prevent or ameliorate the process of epileptogenesis, and (3) treatments for the common comorbidities that contribute to disability in people with epilepsy. New therapies also need to address the special needs of certain subpopulations, that is, age- or gender-specific treatments. Preclinical development in these treatment areas is complex due to heterogeneity in presentation and etiology, and may need to be formulated with a specific seizure, epilepsy syndrome, or comorbidity in mind. The aim of this report is to provide a framework that will help define future guidelines that improve and standardize the design, reporting, and validation of data across preclinical antiepilepsy therapy development studies targeting drug-resistant seizures, epileptogenesis, and comorbidities.

Synthesis and anticonvulsant activity of 1-(8-(benzyloxy)quinolin-2-yl)-6-substituted-4,6-diazaspiro[2,4]heptane-5,7-diones

In the present study on the development of new anticonvulsants, 16 new1-(8-(benzyloxy)quinolin-2-yl-6-substituted-4,6-diazaspiro[2,4]heptane-5,7-diones were synthesized and tested for anticonvulsant activity using the maximal electroshock (MES), subcutaneous pentylenetetrazole (scPTZ) screens, which are the most widely employed seizure models for early identification of candidate anticonvulsants. Their neurotoxicity was determined applying the rotorod test. Two compounds 8e and 8j showed promising anticonvulsant activities in both models employed for anticonvulsant evaluation. The most active compound 8e showed the MES-induced seizures with ED(50) value of 8.6 mg/kg and TD(50) value of 365.3 mg/kg after intraperitoneally injection to mice, which provided compound 8e with a protective index (TD(50)/ED(50)) of 26.8 in the MES test.

New and emerging treatments for epilepsy: review of clinical studies of lacosamide, eslicarbazepine acetate, ezogabine, rufinamide, perampanel, and electrical stimulation therapy

Although many different medical and surgical treatment options for epilepsy exist, approximately 30% of epilepsy patients remain poorly controlled. For those patients who are refractory to medical treatment, epilepsy surgery often provides meaningful improvement. However, when surgical resection of epileptic foci cannot be offered or failed, combined administration of AEDs or the application of novel AEDs is the most appropriate therapeutic options. The most recent AEDs tend to offer new mechanisms of action and more favorable safety profiles than the first generation of AEDs. More recently, alternative options of thalamic or cortical stimulation emerged as potentiall effective treatment for epilepsy. The purpose of this article is to compare and review clinical information for the new and emerging medications such as lacosamide, eslicarbazepine acetate, ezogabine (retigabine), rufinamide, perampanel, as well as deep brain stimulation and responsive neurostimulation devices.

Response to first antiepileptic drug trial predicts health outcome in epilepsy

PURPOSE

Failure to respond to the initial antiepileptic drug (AED) is a predictor of increased risk of pharmacoresistant epilepsy. Whether response to the first AED also predicts adverse health outcomes is unknown.

METHODS

This longitudinal study compared rates of major adverse health outcomes (loss of driving privileges, unemployment, divorce/separation, injury, emergency room admission, hospitalization, and death) in 33 patients who failed the first AED (cases) and 30 patients who became seizure-free with the first AED (controls). Patient data were obtained by chart review and confirmed through a structured interview with each subject at 5-7 years after starting AED treatment. We also assessed between-group differences in quality of life, depression, and adverse AED effects by using standardized instruments completed by each subject at the end of follow-up.

KEY FINDINGS

The number of major adverse health outcomes was similarly high during the first year of AED treatment [mean ± standard deviation (SD) 2.64 ± 0.99 for cases and 2.50 ± 1.14 for controls], but thereafter decreased to a greater extent in controls than in cases (p < 0.001). Controls had a higher cumulative probability of experiencing ≥1 year free from major adverse health outcomes compared to cases (p = 0.002). Two cases died during the follow-up, both of sudden unexpected death. Cases had worse quality of life ratings than controls, whereas no significant between-group differences were found for measures of depression and adverse AED effects. In a post hoc analysis limited to cases, patients who became seizure-free with subsequent AED treatments showed for the first 4 years major adverse health outcome rates similar to those recorded in patients with persisting seizures. After 4 years, however, cases who achieved late seizure freedom tended to show a more favorable outcome.

SIGNIFICANCE

Patients with epilepsy failing the initial AED trial are at increased risk of experiencing adverse health outcomes, at least for the first 4 years after diagnosis. Incorporating these findings into clinical decision making may aid in reducing delays in surgical referrals for pharmacoresistant epilepsy.

Interleukin-1 type 1 receptor/Toll-like receptor signalling in epilepsy: the importance of IL-1beta and high-mobility group box 1

Inflammatory processes in brain tissue have been described in human epilepsy of various aetiologies and in experimental models of seizures. This, together with the anticonvulsant properties of anti-inflammatory therapies both in clinical and in experimental settings, highlights the important role of brain inflammation in the aetiopathogenesis of seizures. Preclinical investigations in experimental models using pharmacological and genetic tools have identified a significant contribution of interleukin-1 (IL-1) type 1 receptor/Toll-like receptor (IL-1R/TLR) signalling to seizure activity. This signalling can be activated by ligands associated with infections (pathogen-associated molecular patterns) or by endogenous molecules, such as proinflammatory cytokines (e.g. IL-1beta) or danger signals [damage-associated molecular patterns, e.g. high-mobility group box 1 (HMGB1)]. IL-1beta and HMGB1 are synthesized and released by astrocytes and microglia in the rodent brain during seizures. Notably, a rapid release of HMGB1 from neurons appears to be triggered by proconvulsant drugs even before seizure occurrence and is involved in their precipitation of seizures. The activation of IL-1R/TLR signalling mediates rapid post-translational changes in N-methyl-d-aspartate-gated ion channels in neurons. A long-term decrease in seizure threshold has also been observed, possibly mediated by transcriptional activation of genes contributing to molecular and cellular plasticity. This emerging evidence identifies specific targets with potential anticonvulsant effects in drug-resistant forms of epilepsy.

Clinical comparability of the new antiepileptic drugs in refractory partial epilepsy: a systematic review and meta-analysis

PURPOSE

Evaluate the clinical comparability of new antiepileptic drugs (AEDs) in partial refractory epilepsy.

METHODS

Systematic review of randomized trials (RCTs) comparing a new AED (add-on treatment) with placebo or another AED.

PRIMARY OUTCOMES

responder (≥50% seizure reduction) and withdrawal (tolerability) rates. Pooled estimates of odds ratios (ORs) and number needed treat/harm (NNT/NNH) taking into account baseline risk were derived by random-effects meta-analysis. Adjusted frequentist indirect comparisons between AEDs were estimated.

KEY FINDINGS

Sixty-two placebo-controlled (12,902 patients) and eight head-to-head RCTs (1,370 patients) were included. Pooled ORs for responder and withdrawal rates (vs. placebo) were 3.00 [95% confidence interval (CI) 2.63-3.41] and 1.48 (1.30-1.68), respectively. Indirect comparisons of responder rate based on relative measurements of treatment effect (ORs) favored topiramate (1.52; 1.06-2.20) in comparison to all other AEDs, whereas gabapentin (0.67; 0.46-0.97) and lacosamide (0.66; 0.48-0.92) were less efficacious, without significant heterogeneity. When analyses were based on absolute estimates (NNTs), topiramate and levetiracetam were more efficacious, whereas gabapentin and tiagabine were less efficacious. Withdrawal rate was higher with oxcarbazepine (OR 1.60; 1.12-2.29) and topiramate (OR 1.68; 1.07-2.63), and lower with gabapentin (OR 0.65; 0.42-1.00) and levetiracetam (OR 0.62; 0.43-0.89).

SIGNIFICANCE

The differences found are of relatively small magnitude to allow a definitive conclusion about which new AED(s) has superior effectiveness. This uncertainty probably reflects the limitations of conclusions based on indirect evidence. The process of pharmacologic clinical decision making in partial refractory epilepsy probably depends more on other aspects, such as individual patient characteristics and pharmacoeconomics, than on available controlled randomized evidence.

Critical review of current animal models of seizures and epilepsy used in the discovery and development of new antiepileptic drugs

Animal models for seizures and epilepsy have played a fundamental role in advancing our understanding of basic mechanisms underlying ictogenesis and epileptogenesis and have been instrumental in the discovery and preclinical development of novel antiepileptic drugs (AEDs). However, there is growing concern that the efficacy of drug treatment of epilepsy has not substantially improved with the introduction of new AEDs, which, at least in part, may be due to the fact that the same simple screening models, i.e., the maximal electroshock seizure (MES) and s.c. pentylenetetrazole (PTZ) seizure tests, have been used as gatekeepers in AED discovery for >6 decades. It has been argued that these old models may identify only drugs that share characteristics with existing drugs, and are unlikely to have an effect on refractory epilepsies. Indeed, accumulating evidence with several novel AEDs, including levetiracetan, has shown that the MES and PTZ models do not identify all potential AEDs but instead may fail to discover compounds that have great potential efficacy but work through mechanisms not tested by these models. Awareness of the limitations of acute seizure models comes at a critical crossroad. Clearly, preclinical strategies of AED discovery and development need a conceptual shift that is moving away from using models that identify therapies for the symptomatic treatment of epilepsy to those that may be useful for identifying therapies that are more effective in the refractory population and that may ultimately lead to an effective cure in susceptible individuals by interfering with the processes underlying epilepsy. To realize this goal, the molecular mechanisms of the next generation of therapies must necessarily evolve to include targets that contribute to epileptogenesis and pharmacoresistance in relevant epilepsy models.

Factors determining response to antiepileptic drugs in randomized controlled trials. A systematic review and meta-analysis

PURPOSE

Because of the lack of head-to-head adjunctive-therapy trials of antiepileptic drugs (AEDs) in refractory partial epilepsy, meta-analyses of placebo-controlled randomized controlled trials (RCTs) represent a potentially important source of evidence to guide treatment decisions. However, such indirect comparisons raise various methodologic issues that may hamper their relevance.

METHODS

All RCTs in adult refractory partial epilepsy were analyzed to assess whether efficacy outcomes are influenced by: characteristics of patients and trials ; use of last observation carried forward (LOCF) analysis; evaluation period (entire period versus maintenance period); and year of publication. A meta-analysis of these AEDs was then performed taking these factors into consideration.

KEY FINDINGS

Sixty-three RCTs evaluating 20 AEDs were included. The following variables influenced efficacy estimates: (1) responder rates correlated positively with duration of the entire treatment period (p = 0.038); (2) response to placebo was significantly greater in the maintenance period than in the entire treatment period (p = 0.005); (3) responder rates increased over the years both for AEDs (p < 0.001) and for placebo (p = 0.001); (4) LOCF analysis overestimated responder rates for AEDs (p < 0.001) and for placebo (p = 0.001) compared with completer-based analysis, and the overestimation correlated positively with withdrawal rates (p < 0.001). A meta-analysis of available data showed large differences in efficacy ranking in relation to dose selection and type of analysis, but these were mostly nonsignificant due to statistical power limitations.

SIGNIFICANCE

Several methodologic issues hamper the relevance of indirect comparisons of AEDs in the adjunctive-therapy of refractory partial epilepsy. Some of these issues could be overcome by improved standardization in the reporting of efficacy outcomes.

Orphenadrine induces secondarily generalized convulsive status epilepticus in rats

The current study was aimed to assess the convulsant potency of orphenadrine (ORPH) in rats together with a screen of different conventional antiepileptic drugs (AEDs) on their efficacy to suppress it. ORPH was administered intraperitoneally (i.p.) in doses of 50-80 mg/kg in male Wistar rats. The latency to first seizure, the number of seizure episodes and the duration of overt status epilepticus (SE) as well as the incidence of deaths was scored with simultaneous electroencephalographic (EEG) recordings. Subsequently, the effects of conventional AEDs on ORPH-evoked (80 mg/kg) seizure incidence were studied. ORPH dose-dependently induced seizures in increasing number of animals, reaching 100% at a dose of 80 mg/kg, associated with low mortality and no drug-related neurotoxicity. Epileptic attacks started as complex partial fits consisting of stereotyped behavior, limb movements, head shaking and myoclonic twitches of the body. Subsequently, an overt generalized convulsive SE appeared, lasting for approximately 2h. Among conventional AEDs: carbamazepine, ethosuximide and phenytoin had no effect while valproate (p<0.001), diazepam (p<0.01), and phenobarbital (p<0.001) dose-dependently suppressed seizure activity. All the above characteristics make the new model, a useful, easy to perform experimental tool to study the pathophysiology of SE as well as the effects of new AEDs.

Synthesis and anticonvulsant activity of 8-alkoxy-5,6-dihydro-4H-[1,2,4]triazolo[4,3-a][1]benzazepin-1-one derivatives

A series of novel 8-alkoxy-5,6-dihydro-4H-[1,2,4]triazolo[4,3-a][1]benzazepin-1-one derivatives were synthesized and screened for their anticonvulsant activities by the maximal electroshock (MES) test, subcutaneous pentylenetetrazol (scPTZ) test, and their neurotoxicity was evaluated by the rotarod neurotoxicity test (Tox). The results of these tests demonstrated that 8-heptyloxy-5,6-dihydro-4H-[1,2,4]triazolo[4,3-a][1]benzazepin-1-one (3f) and 8-hexyloxy -5,6-dihydro-4H-[1,2,4]triazolo[4,3-a][1]benzazepin-1-one (3e) were the most promising compounds, with median effective dose (ED(50)) of 17.6 and 17.9 mg/kg, and protective index (PI) of greater than 63.4 and 62.4 in the MES test, respectively. These PI values were higher than the PI value of the prototype antiepileptic drug carbamazepine. The scPTZ test showed that 8-pentyloxy-5,6-dihydro-4H-[1,2,4]triazolo[4,3-a][1]benzazepin-1-one (3d) was the most potent with ED(50) value of 38.0 mg/kg and PI value of greater than 29.4, which is much safer than marketed drug carbamazepine. The possible structure-activity relationship was discussed.

The role of inflammation in epilepsy

Epilepsy is the third most common chronic brain disorder, and is characterized by an enduring predisposition to generate seizures. Despite progress in pharmacological and surgical treatments of epilepsy, relatively little is known about the processes leading to the generation of individual seizures, and about the mechanisms whereby a healthy brain is rendered epileptic. These gaps in our knowledge hamper the development of better preventive treatments and cures for the approximately 30% of epilepsy cases that prove resistant to current therapies. Here, we focus on the rapidly growing body of evidence that supports the involvement of inflammatory mediators-released by brain cells and peripheral immune cells-in both the origin of individual seizures and the epileptogenic process. We first describe aspects of brain inflammation and immunity, before exploring the evidence from clinical and experimental studies for a relationship between inflammation and epilepsy. Subsequently, we discuss how seizures cause inflammation, and whether such inflammation, in turn, influences the occurrence and severity of seizures, and seizure-related neuronal death. Further insight into the complex role of inflammation in the generation and exacerbation of epilepsy should yield new molecular targets for the design of antiepileptic drugs, which might not only inhibit the symptoms of this disorder, but also prevent or abrogate disease pathogenesis.

Enantioselective assay for therapeutic drug monitoring of eslicarbazepine acetate: no interference with carbamazepine and its metabolites

As add-on therapy, phase III clinical trials of eslicarbazepine acetate (ESL) conducted in patients with refractory partial-onset seizures have shown good efficacy, safety, and tolerability, even in patients taking carbamazepine (CBZ) at baseline (approximately 60% of the enrolled patients). Thus, considering the pharmacological disadvantages of CBZ and the similar efficacy spectrum of CBZ and ESL, switching to ESL may be successful in many patients. As ESL is a prodrug almost instantaneously converted to S-licarbazepine (S-Lic; approximately 95%), an interest in therapeutic drug monitoring (TDM) of S-Lic is likely to develop in the future. This study investigated the plasma concentrations of S-Lic and R-licarbazepine (R-Lic) enantiomers in patients under CBZ long-term treatment to assess the potential interference of CBZ or its metabolites in the enantioselective TDM of ESL (using S-Lic concentrations). A chiral high-performance liquid chromatography assay with ultraviolet detection (HPLC-UV) previously developed and validated by our research group was used. Twenty-four patients admitted to the Coimbra University Hospital and supposedly receiving CBZ long-term treatment were identified. Blood samples were collected from patients and serum CBZ concentrations were measured by the usual TDM protocol. Aliquots of plasma from such patients were also submitted to a chiral HPLC-UV analysis. The bioanalytical data indicated that S-Lic and R-Lic were not present at detectable concentrations in plasma samples of the CBZ-treated patients. The chromatograms generated by the analysis of patient plasma samples, when compared with those obtained from blank plasma samples spiked with S-Lic and R-Lic, clearly showed the absence of interferences at the retention times of both Lic enantiomers. These data support the usefulness of the chiral HPLC-UV method used for the enantioselective TDM of ESL (using S-Lic) for programs in which switching from CBZ to ESL is implemented.

A randomized, double-blind, placebo-controlled, parallel-group study of rufinamide as adjunctive therapy for refractory partial-onset seizures

PURPOSE

Efficacy and safety of adjunctive rufinamide (3,200 mg/day) was assessed in adolescents and adults with inadequately controlled partial-onset seizures receiving maintenance therapy with up to three antiepileptic drugs (AEDs).

METHODS

This randomized, double-blind, placebo-controlled, parallel-group, multicenter study comprised a 56-day baseline phase (BP), 12-day titration phase, and 84-day maintenance phase (MP). The primary efficacy variable was percentage change in total partial seizure frequency per 28 days (MP vs. BP). Secondary efficacy outcome measures included ≥50% responder rate and reduction in mean total partial seizure frequency during the MP. Safety and tolerability evaluation included adverse events (AEs), physical and neurologic examinations, and laboratory values. Pharmacokinetic and pharmacodynamic assessments were conducted.

RESULTS

Three hundred fifty-seven patients were randomized: 176 to rufinamide and 181 to placebo. Patients had a median of 13.3 seizures per 28 days during BP; 86% were receiving ≥2 AEDs. For the intent-to-treat population, the median percentage reduction in total partial seizure frequency per 28 days was 23.25 for rufinamide versus 9.80 for placebo (p = 0.007). Rufinamide-treated patients were more than twice as likely to have had a ≥50% reduction in partial seizure frequency (32.5% vs. 14.3%; p < 0.001) and had a greater reduction in median total partial seizure rate per 28 days during the MP (13.2 vs. 5.2; p < 0.001). Treatment-emergent AEs occurring at ≥5% higher incidence in the rufinamide group compared with placebo were dizziness, fatigue, nausea, somnolence, and diplopia.

CONCLUSIONS

Adjunctive treatment with rufinamide reduced total partial seizures in refractory patients. AEs reported were consistent with the known tolerability profile of rufinamide.

Lacosamide for the prevention of partial onset seizures in epileptic adults

Lacosamide is a newly registered antiepileptic drug with dual mechanisms of action. It selectively enhances slow inactivation of voltage-gated sodium channels, resulting in stabilization of hyperexcitable neuronal membranes and inhibition of repetitive neuronal firing. It also binds to a collapsing-response mediator protein-2, CRMP2. Lacosamide has a favorable pharmacokinetic profile; is rapidly and completely absorbed, has a relatively long elimination half-life of 13 hours which allows twice-daily administration, linear pharmacokinetics, and has low potential for drug interactions and renal elimination. Both oral and intravenous formulations of lacosamide are being developed. In placebo-controlled clinical trials, lacosamide was effective in seizure reduction as adjunctive therapy in patients with uncontrolled partial-onset seizures. Lacosamide was generally well tolerated. The most frequently reported adverse events in placebo-controlled trials were dizziness, headache, nausea, and diplopia. Intravenous lacosamide has a comparably good safety profile.

Lacosamide: new adjunctive treatment option for partial-onset seizures

IMPORTANCE OF THE FIELD

Epilepsy is one of the most common neurological disorders, affecting up to 2% of the population worldwide. Studies show that patients with refractory seizures have higher morbidity and mortality rates, as well as a poorer quality of life, than those with controlled seizures. Therefore, treatment that reduces the frequency of seizures may improve patients' quality of life. Lacosamide (LCM) is a recently approved anticonvulsant in Europe and the USA which offers new mechanisms of action and favorable safety profiles. Efficacy data have shown fast onset of anticonvulsant effects and significant reduction of partial-onset seizures as adjunctive therapy at LCM 200 and 400 mg/day, even in a severely refractory population.

AREAS COVERED IN THIS REVIEW

This article reviews three pivotal clinical trials of LCM, including its efficacy and tolerability over 7 years. In addition, LCM's key pharmacodynamics and pharmacokinetics from a search of the literature are reviewed in detail. This article also includes recent publications on the safety and use of intravenous LCM solution for patients with epilepsy.

WHAT THE READER WILL GAIN

This article provides comprehensive review of efficacy and safety information of LCM along with comprehensive pharmacokinetic information, which includes absolute bioavailability, low protein binding, lack of hepatic enzyme induction or inhibition, and low potential for drug-drug interactions.

TAKE HOME MESSAGE

Considering the fact that more than 30% of epilepsy patients remain refractory despite various antiepileptic drugs, LCM may provide added benefit to patients with refractory seizures.

Difficulties in Treatment and Management of Epilepsy and Challenges in New Drug Development

Epilepsy is a serious neurological disorder that affects around 50 million people worldwide. Almost 30% of epileptic patients suffer from pharmacoresistance, which is associated with social isolation, dependent behaviour, low marriage rates, unemployment, psychological issues and reduced quality of life. Currently available antiepileptic drugs have a limited efficacy, and their negative properties limit their use and cause difficulties in patient management. Antiepileptic drugs can provide only symptomatic relief as these drugs suppress seizures but do not have ability to cure epileptogenesis. The long term use of antiepileptic drugs is limited due to their adverse effects, withdrawal symptoms, deleterious interactions with other drugs and economic burden, especially in developing countries. Furthermore, some of the available antiepileptic drugs may even potentiate certain type of seizures. Several in vivo and in vitro animal models have been proposed and many new antiepileptic drugs have been marketed recently, but large numbers of patients are still pharmacoresistant. This review will highlight the difficulties in treatment and management of epilepsy and the limitations of available antiepileptic drugs and animal seizure models.

Toll-like receptor 4 and high-mobility group box-1 are involved in ictogenesis and can be targeted to reduce seizures

Brain inflammation is a major factor in epilepsy, but the impact of specific inflammatory mediators on neuronal excitability is incompletely understood. Using models of acute and chronic seizures in C57BL/6 mice, we discovered a proconvulsant pathway involving high-mobility group box-1 (HMGB1) release from neurons and glia and its interaction with Toll-like receptor 4 (TLR4), a key receptor of innate immunity. Antagonists of HMGB1 and TLR4 retard seizure precipitation and decrease acute and chronic seizure recurrence. TLR4-defective C3H/HeJ mice are resistant to kainate-induced seizures. The proconvulsant effects of HMGB1, like those of interleukin-1beta (IL-1beta), are partly mediated by ifenprodil-sensitive N-methyl-d-aspartate (NMDA) receptors. Increased expression of HMGB1 and TLR4 in human epileptogenic tissue, like that observed in the mouse model of chronic seizures, suggests a role for the HMGB1-TLR4 axis in human epilepsy. Thus, HMGB1-TLR4 signaling may contribute to generating and perpetuating seizures in humans and might be targeted to attain anticonvulsant effects in epilepsies that are currently resistant to drugs.

New treatment option for partial-onset seizures: efficacy and safety of lacosamide

More than 30% of epilepsy patients remain refractory despite the advent of new antiepileptic drugs (AEDs) over two decades. Although a small percentage of these refractory patients may become seizure free when a new AED is added, combined administration of AEDs or the application of novel AEDs is the most common therapeutic option when surgical treatment cannot be offered. The most recently approved AED in Europe and the USA is lacosamide (LCM), which offers new mechanisms of action and favorable safety profiles. This article reviews LCM's molecular mechanisms of action, pharmacokinetic profiles as well as efficacy and safety from phase II and III clinical trials. In addition, comparison between LCM and other existing AEDs is discussed.

New and investigational antiepileptic drugs

In the last fifteen years, new antiepileptic medications have been offered for the treatment of patients with epilepsy. Nevertheless, despite optimal medical treatment, up to 30% of patients still experience recurrent seizures and the challenge for new, more efficacious and better-tolerated drugs continues. New antiepileptic drugs include the evolution of pre-existing drugs and new compounds identified through the investigation of additional molecular targets, such as SV2A synaptic vesicle protein, voltage-gated potassium channels, ionotropic and metabotropic glutamate receptors, and gap junctions. This paper reviews the available information on various classes of molecules that are in the pipeline as well as on the innovative approaches to the treatment of epilepsy.

Key factors in the discovery and development of new antiepileptic drugs

Since the early 1990s, many new antiepileptic drugs (AEDs) that offer appreciable advantages in terms of their favourable pharmacokinetics, improved tolerability and lower potential for drug-drug interactions have entered the market. However, despite the therapeutic arsenal of old and new AEDs, approximately 30% of patients with epilepsy still suffer from seizures. Thus, there remains a substantial need for the development of more efficacious AEDs for patients with refractory seizures. Here, we briefly review the emerging knowledge on the pathological basis of epilepsy and how it might best be used in the design of new therapeutics. We also discuss the current approach to AED discovery and highlight some of the unique features of newer models of pharmacoresistance and epileptogenesis that have emerged in recent years.

Comparative study of five antiepileptic drugs on a translational cognitive measure in the rat: relationship to antiepileptic property

RATIONALE

Antiepileptic drugs (AEDs) have been available for many years; yet, new members of this class continue to be identified and developed due to the limitations of existing drugs, which include a propensity for cognitive impairment. However, there is little preclinical information about the cognitive effects they produce, which clinically include deficits in attention and slowing of reaction time.

OBJECTIVES

The purpose of this study was to profile two first-generation AEDs, phenytoin and valproate, and three second-generation AEDs, levetiracetam, pregabalin and lacosamide. Initially, each drug was examined across a range of well characterised preclinical seizure tests, and then each drug was evaluated in the five-choice serial reaction time test (5-CSRTT) based on efficacious doses from the seizure tests.

MATERIALS AND METHODS

Each AED was tested for anti-seizure efficacy in either (1) the maximal electroshock seizure test, (2) s.c. PTZ seizure test, (3) amygdala-kindled seizures and (4) the genetic absence epilepsy rat of Strasbourg model of absence seizures. On completion of these studies, each drug was tested in rats trained to asymptotic performance in the 5-CSRTT (0.5 s SD, 5 s ITI, 100 trials). Male rats were used in all studies.

RESULTS

Each AED was active in at least one of the seizure tests, although only valproate was active in each test. In the 5-CSRT test, all drugs with the exception of levetiracetam, significantly slowed reaction time and increased omissions. Variable effects were seen on accuracy. The effect on omissions was reversed by increasing stimulus duration from 0.5 to 5 s, supporting a drug-induced attention deficit. Levetiracetam had no negative effect on performance; indeed, reaction time was slightly increased (i.e. faster).

CONCLUSIONS

These results highlight somewhat similar effects of phenytoin, valproate, pregabalin and lacosamide on attention and reaction time, and comparison to efficacious doses from the seizure tests support the view that there may be a better separation with the newer AEDs. Levetiracetam had no detrimental effect in the 5-CSRTT, which may be consistent with clinical experience where the drug is considered to be well tolerated amongst the AED class.

Eslicarbazepine acetate: a new option for the treatment of focal epilepsy

BACKGROUND

Epilepsy is a neurological condition with an increased probability of seizure occurrence through time. Although many anti-epileptic drugs (AEDs) exist, they fail to treat seizures in 30% of patients with epilepsy. For these patients, new AEDs potentially more efficacious and safe are developed.

OBJECTIVE

To evaluate the effectiveness of eslicarbazepine acetate (ESL) in the treatment of patients with refractory epilepsy.

METHODS

A review of the literature was carried out using PubMed central. A direct contact with the drug manufacturer and developer was made.

RESULTS/CONCLUSION

ESL is an AED that acts by inhibiting voltage-gated sodium channels. It has proved efficacious in the treatment of patients with refractory focal-onset epilepsy with a good safety profile. Evaluation of its use for treating other epileptic syndromes and its role as an initial treatment option for patients with epilepsy is warranted.

Designing clinical trials to assess antiepileptic drugs as monotherapy : difficulties and solutions

Designing monotherapy trials in epilepsy is fraught with many hurdles, including diagnostic and classification difficulties, sparse information regarding the natural history of the disorder, and ethical objections to the use of placebo or a suboptimal comparator in a condition where the consequences of therapeutic failure can be serious. These issues are further complicated by regulatory differences between the US and the EU.In the US, the FDA considers that evidence of efficacy requires demonstration of superiority to a comparator. Because available antiepileptic drugs possess relatively high efficacy, in most settings it is unrealistic to expect that a new treatment will be superior to a standard treatment used at optimized dosages. To circumvent this problem, trial designs have been developed whereby patients in the control group are assigned to receive a suboptimal comparator and are required to exit from the trial if seizure deterioration occurs. This allows demonstration of a between-group difference in efficacy endpoints, such as time to exit or time to first seizure. Although these trials have come under increasing criticism because of ethical concerns, extensive information is now available on the outcome of patients with chronic epilepsy randomized to suboptimal treatment in similarly designed conversion to monotherapy trials. This has allowed the construction of a dataset of historical controls against which response to a fully active treatment can be compared. A number of studies using this novel approach are now in progress.In the EU, in addition to requiring data on conversion to monotherapy in refractory patients, the European Medicines Agency stipulates that a monotherapy indication in newly diagnosed epilepsy can only be granted if a candidate drug has shown at least a similar benefit/risk balance compared with an acknowledged standard at its optimal use during an assessment period of no less than 1 year. This has led to the implementation of noninferiority trials, one of which has been completed and which led to approval of the monotherapy indication for levetiracetam in the EU. Noninferiority trials provide valuable data in a setting that most closely resembles routine clinical practice, but their interpretation can be complicated by uncertainties on assay sensitivity.Major evidence gaps in the treatment of epilepsy still remain and it is hoped that these will be addressed in the near future. High quality monotherapy trials are particularly needed to assess the comparative efficacy of older and newer drugs in less common epilepsy syndromes, including most generalized epilepsies, and to investigate the different treatment options in populations homogeneous not only in terms of syndromic classification, but also in terms of underlying aetiology and associated phenotypes.

Lacosamide: a new approach to target voltage-gated sodium currents in epileptic disorders

The mechanism of action of several antiepileptic drugs (AEDs) rests on their ability to modulate the activity of voltage-gated sodium currents that are responsible for fast action potential generation. Recent data indicate that lacosamide (a compound with analgesic and anticonvulsant effects in animal models) shares a similar mechanism. When compared with other AEDs, lacosamide has the unique ability to interact with sodium channel slow inactivation without affecting fast inactivation. This article reviews these findings and discusses their relevance within the context of neuronal activity seen during epileptiform discharges generated by limbic neuronal networks in the presence of chemical convulsants. These seizure-like events are characterized by sustained discharges of sodium-dependent action potentials supported by robust depolarizations, thus providing synchronization within neuronal networks. Generally, AEDs such as phenytoin, carbamazepine and lamotrigine block sodium channels when activated. In contrast, lacosamide facilitates slow inactivation of sodium channels both in terms of kinetics and voltage dependency. This effect may be relatively selective for repeatedly depolarized neurons, such as those participating in seizure activity in which the persistence of sodium currents is more pronounced and promotes neuronal excitation. The clinical effectiveness of lacosamide has been demonstrated in randomized, double-blind, parallel-group, placebo-controlled, adjunctive-therapy trials in patients with refractory partial seizures. Further studies should determine whether the effects of lacosamide in animal models and in clinical settings are fully explained by its selective action on sodium current slow inactivation or whether other effects (e.g. interactions with the collapsin-response mediator protein-2) play a contributory role.

Treatment of Lennox-Gastaut syndrome: overview and recent findings

Lennox-Gastaut syndrome (LGS) is a rare, age-related syndrome, characterized by multiple seizure types, a specific electro-encephalographic pattern, and mental regression. However, published data on the etiology, evolution, and therapeutic approach of LGS are contradictory, partly because the precise definition of LGS used in the literature varies. In the most recent classification, LGS belongs to the epileptic encephalopathies and is highly refractory to all antiepileptic drugs. Numerous treatments, medical and non-medical, have been proposed and results mostly from open studies or case series have been published. Sometimes, patients with LGS are included in a more global group of patients with refractory epilepsy. Only 6 randomized double-blind controlled trials of medical treatments, which included patients with LGS, have been published. Overall, treatment is rarely effective and the final prognosis remains poor in spite of new therapeutic strategies. Co-morbidities need specific treatment. This paper summarizes the definition, diagnosis and therapeutic approach to LGS, including not only recognized antiepileptic drugs, but also "off label" medications, immune therapy, diet, surgery and some perspectives for the future.

Anticonvulsant profile and teratogenicity of 3,3-dimethylbutanoylurea: a potential for a second generation drug to valproic acid

PURPOSE

The purpose of this study was to evaluate the anticonvulsant activity and teratogenic potential of branched aliphatic acylureas represented by isovaleroylurea (IVU), pivaloylurea (PVU) and 3,3-dimethylbutanoylurea (DBU), as potential second-generation drugs to valproic acid (VPA).

METHODS

The anticonvulsant activity of IVU, PVU, and DBU was determined in mice and rats utilizing the maximal electroshock seizure (MES) and the pentylenetetrazole (scMet) tests. The ability of DBU to block electrical-, or chemical-induced seizures was further examined in three acute seizure models: the psychomotor 6 Hz model, the bicuculline and picrotoxin models and one model of chronic epilepsy (i.e., the hippocampal kindled rat model). The induction of neural tube defects (NTDs) by IVU, PVU, and DBU was evaluated after i.p. administration at day 8.5 of gestation to a mouse strain highly susceptible to VPA-induced teratogenicity. The pharmacokinetics of DBU was studied following i.v. administration to rats.

RESULTS

DBU emerged as the most potent compound having an MES-ED(50)of 186 mg/kg (mice) and 64 mg/kg (rats) and an scMet-ED(50)of 66 mg/kg (mice) and 26 mg/kg (rats). DBU underwent further evaluation in the hippocampal kindled rat (ED(50)= 35 mg/kg), the psychomotor 6 Hz mouse model (ED(50)= 80 mg/kg at 32 mA and ED(50)= 133 mg/kg at 44 mA), the bicuculline- and picrotoxin-induced seizure mouse model (ED(50)= 205 mg/kg and 167 mg/kg, respectively). In contrast to VPA, DBU, IVU, and PVU did not induce a significant increase in NTDs as compared to control. DBU was eliminated by metabolism with a half-life of 4.5 h.

CONCLUSIONS

DBU's broad spectrum and potent anticonvulsant activity, along with its high safety margin and favorable pharmacokinetic profile, make it an attractive candidate to become a new, potent, and safe AED.

Intractable epilepsy: management and therapeutic alternatives

More than half of patients with newly diagnosed epilepsy achieve complete seizure control without major side-effects. Patients who continue to have seizures after initial medical therapy should have an early and detailed assessment to confirm the diagnosis, to determine the underlying cause and epilepsy syndrome, and to choose an adequate treatment strategy. The risks and potential benefits of surgical procedures or experimental therapy have to be weighed against the chance of improvement and the potential side-effects of additional medical therapy. Surgery for temporal lobe epilepsy, the most common cause of focal epilepsy, can control seizures and improve quality of life in appropriately selected patients. However, around 20-30% of patients do not respond to medical or surgical treatment. The management of chronic intractable epilepsy requires comprehensive care to address the adverse events of medical treatment, quality of life issues, and comorbid disorders. Much research focuses on the experimental treatment options that offer hope of seizure reduction or cure.