Carisbamate as adjunctive treatment of partial onset seizures in adults in two randomized, placebo-controlled trials

Cenobamate Plasma Levels in Patients with Epilepsy: Correlation with Efficacy and Tolerability?

Objective: Cenobamate is approved by the European Medicine Agency for the treatment of adult patients with epilepsy (PWEs) with ongoing focal-onset seizures despite appropriate treatment with at least two established antiseizure medications. Pivotal trials and post-marketing real-world observational studies suggest high efficacy with unusually high seizure-free rates. The authors sought to investigate the plasma levels of cenobamate under steady-state conditions in seizure-free versus non-responding PWEs, and in PWEs who experienced adverse events versus those who did not. Methods: Blood samples were collected from adult PWEs who were treated with adjunct cenobamate under steady-state conditions. Daily doses, concomitant medications, efficacy, and tolerability were assessed. The plasma cenobamate levels of seizure-free versus non-responding PWEs and between PWEs with and those without clinical adverse events were compared. Results: Samples from 101 PWEs were included. Thirty-six PWEs were seizure-free and 65 were non-responders. In 31 PWEs, adverse events were apparent, whereas in the remaining 70, no tolerability issues were reported. A linear correlation was found between the daily doses (range: 100 mg-400 mg) and the plasma levels (3.8 mg/L-54.6 mg/L). Neither the daily doses nor the plasma levels differed significantly between the investigated subgroups. The main reason for this result was that the individual therapeutic ranges varied widely: seizure freedom and adverse effects were observed alongside low doses and plasma levels in some PWEs. Conversely, there were examples of PWEs who did not respond or who reported no tolerability issues at high doses or plasma levels. Conclusions: To evaluate the individual therapeutic range and to better understand the influence of other drugs in cases where concomitant medications are used, the therapeutic drug monitoring of cenobamate may be useful. A general therapeutic range cannot be defined.

Lennox-Gastaut Syndrome: Current Treatments, Novel Therapeutics, and Future Directions

Lennox-Gastaut syndrome is a severe drug-resistant developmental and epileptic encephalopathy with slow spike and wave on EEG (DEE-SSW) composing about 1-2% of epilepsy patients. Seizures in DEE-SSW are caused by a variety of etiologies, and there is a large unmet treatment need as seizures are usually treatment-resistant and individuals are often unable to function independently. The updated definition by the International League Against Epilepsy has established formal diagnostic criteria allowing for more uniform diagnosis. This article provides a review of typical medication management and treatment strategies, including new and developing surgical approaches. Future directions in treatment include expanding genetic testing with the potential for gene therapy and continuously improving surgical options with the goal to prevent progression to DEE-SSW.

Cenobamate (YKP3089) and Drug-Resistant Epilepsy: A Review of the Literature

Cenobamate (CNB), ([(R)-1-(2-chlorophenyl)-2-(2H-tetrazol-2-yl)ethyl], is a novel tetrazole alkyl carbamate derivative. In November 2019, the Food and Drug Administration approved Xcopri®, marketed by SK Life Science Inc., (Paramus, NJ, USA) for adult focal seizures. The European Medicines Agency approved Ontozry® by Arvelle Therapeutics Netherlands B.V.(Amsterdam, The Neatherlands) in March 2021. Cenobamate is a medication that could potentially change the perspectives regarding the management and prognosis of refractory epilepsy. In this way, this study aims to review the literature on CNB's pharmacological properties, pharmacokinetics, efficacy, and safety. CNB is a highly effective drug in managing focal onset seizures, with more than twenty percent of individuals with drug-resistant epilepsy achieving seizure freedom. This finding is remarkable in the antiseizure medication literature. The mechanism of action of CNB is still poorly understood, but it is associated with transient and persistent sodium currents and GABAergic neurotransmission. In animal studies, CNB showed sustained efficacy and potency in the 6 Hz test regardless of the stimulus intensity. CNB was revealed to be the most cost-effective drug among different third-generation antiseizure medications. Also, CNB could have neuroprotective effects. However, there are still concerns regarding its potential for abuse and suicidality risk, which future studies should clearly assess, after which protocols should be changed. The major drawback of CNB therapy is the slow and complex titration and maintenance phases preventing the wide use of this new agent in clinical practice.

Concerted suppressive effects of carisbamate, an anti-epileptic alkyl-carbamate drug, on voltage-gated Na+ and hyperpolarization-activated cation currents

Carisbamate (CRS, RWJ-333369) is a new anti-seizure medication. It remains unclear whether and how CRS can perturb the magnitude and/or gating kinetics of membrane ionic currents, despite a few reports demonstrating its ability to suppress voltage-gated Na+ currents. In this study, we observed a set of whole-cell current recordings and found that CRS effectively suppressed the voltage-gated Na+ (INa) and hyperpolarization-activated cation currents (Ih) intrinsically in electrically excitable cells (GH3 cells). The effective IC50 values of CRS for the differential suppression of transient (INa(T)) and late INa (INa(L)) were 56.4 and 11.4 μM, respectively. However, CRS strongly decreased the strength (i.e., Δarea) of the nonlinear window component of INa (INa(W)), which was activated by a short ascending ramp voltage (Vramp); the subsequent addition of deltamethrin (DLT, 10 μM) counteracted the ability of CRS (100 μM, continuous exposure) to suppress INa(W). CRS strikingly decreased the decay time constant of INa(T) evoked during pulse train stimulation; however, the addition of telmisartan (10 μM) effectively attenuated the CRS (30 μM, continuous exposure)-mediated decrease in the decay time constant of the current. During continued exposure to deltamethrin (10 μM), known to be a pyrethroid insecticide, the addition of CRS resulted in differential suppression of the amplitudes of INa(T) and INa(L). The amplitude of Ih activated by a 2-s membrane hyperpolarization was diminished by CRS in a concentration-dependent manner, with an IC50 value of 38 μM. For Ih, CRS altered the steady-state I-V relationship and attenuated the strength of voltage-dependent hysteresis (Hys(V)) activated by an inverted isosceles-triangular Vramp. Moreover, the addition of oxaliplatin effectively reversed the CRS-mediated suppression of Hys(V). The predicted docking interaction between CRS and with a model of the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel or between CRS and the hNaV1.7 channel reflects the ability of CRS to bind to amino acid residues in HCN or hNaV1.7 channel via hydrogen bonds and hydrophobic interactions. These findings reveal the propensity of CRS to modify INa(T) and INa(L) differentially and to effectively suppress the magnitude of Ih. INa and Ih are thus potential targets of the actions of CRS in terms of modulating cellular excitability.

Carisbamate add-on therapy for drug-resistant focal epilepsy

BACKGROUND

Epilepsy is one of the most common neurological disorders. Many people with epilepsy are drug-resistant and require add-on therapy, meaning that they concomitantly take multiple antiepileptic drugs. Carisbamate is a drug which is taken orally and inhibits voltage-gated sodium channels. Carisbamate may be useful for drug-resistant focal epilepsy.

OBJECTIVES

To evaluate the efficacy and tolerability of carisbamate when used as an add-on therapy for drug-resistant focal epilepsy.

SEARCH METHODS

We searched the following databases on 8 April 2021: Cochrane Register of Studies (CRS Web) and MEDLINE (Ovid) 1946 to April 07, 2021. CRS Web includes randomised or quasi-randomised controlled trials from PubMed, Embase, ClinicalTrials.gov, WHO ICTRP, the Cochrane Central Register of Controlled Trials (CENTRAL), and the specialised registers of Cochrane review groups including Epilepsy. We also searched ongoing trials registers, checked reference lists, and contacted authors of the included trials.

SELECTION CRITERIA

Double-blind randomised controlled trials (RCTs) comparing carisbamate versus placebo or another antiepileptic drug, as add-on therapy for drug-resistant focal epilepsy. Trials could have a parallel-group or cross-over design.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected the trials for inclusion, assessed trial quality, and extracted data. The primary outcome was 50% or greater reduction in seizure frequency (responder rate). The secondary outcomes were: seizure freedom, treatment withdrawal (for any reason and due to adverse events); adverse events, and quality of life. We analysed data using the Mantel-Haenszel statistical method and according to the intention-to-treat population. We presented results as risk ratios (RRs) with 95% confidence intervals (CIs).

MAIN RESULTS

We included four RCTs involving a total of 2211 participants. All four trials compared carisbamate with placebo for drug-resistant focal epilepsy. Participants in all trials were over 16 years of age and received at least one other antiepileptic drug concomitantly. We detected substantial risk of bias across the included trials. All four trials were at high risk of attrition bias due to the incomplete reporting of attrition and the high treatment withdrawal rates noted, especially with higher doses. All four trials also had unclear risk of detection bias, as they did not specify whether outcome assessors were blinded. Meta-analysis suggested that carisbamate produced a higher responder rate compared to placebo (RR 1.36, 95% CI 1.14 to 1.62; 4 studies; moderate-certainty evidence). More participants in the carsibamate group achieved seizure freedom (RR 2.43, 95% CI 0.84 to 7.03; 1 study); withdrew from treatment for any reason (RR 1.32, 95% CI 0.82 to 2.12; 4 studies); and withdrew from treatment due to adverse events (RR 1.80, 95% CI 0.78 to 4.17; 4 studies) than in the placebo group. However, the evidence for the three outcomes was very low-certainty. There was no difference between treatment groups for the proportion of participants experiencing at least one adverse event (RR 1.10, 95% CI 0.93 to 1.30; 2 studies; low-certainty evidence). More participants in the carisbamate group than in the placebo group developed dizziness (RR 2.06, 95% CI 1.23 to 3.44; 4 studies; very low-certainty evidence) and somnolence (RR 1.82, 95% CI 1.28 to 2.58; 4 studies; low-certainty evidence), but not fatigue (RR 1.11, 95% CI 0.73 to 1.68; 3 studies); headache (RR 1.13, 95% CI 0.92 to 1.38; 4 studies); or nausea (RR 1.19, 95% CI 0.81 to 1.75; 3 studies). None of the included trials reported quality of life.

AUTHORS' CONCLUSIONS

The results suggest that carisbamate may demonstrate efficacy and tolerability as an add-on therapy for drug-resistant focal epilepsy. Importantly, the evidence for all outcomes except responder rate was of low to very low certainty, therefore we are uncertain of the accuracy of the reported effects. The certainty of the evidence is limited by the significant risk of bias associated with the included studies, as well as the statistical heterogeneity detected for some outcomes. Consequently, it is difficult for these findings to inform clinical practice. The studies were all of short duration and only included adult study populations. There is a need for further RCTs with more clear methodology, long-term follow-up, more clinical outcomes, more seizure types, and a broader range of participants.

Cenobamate tablets as a treatment for focal-onset seizures in adults

Introduction: Despite the introduction of numerous new antiseizure medications (ASMs) still about one-third of epilepsies remain drug-resistant. Therefore, new compounds with advanced efficacy are urgently needed. Cenobamate (CNB) is a new ASM that has been recently introduced in the United States for the treatment of adults with focal-onset seizures. The approval in Europe is under way.Areas covered: This review covers the pharmacological profile of CNB, the proof-of-concept trial, the two double-blind, placebo-controlled phase 2 trials investigating adjunct CNB in adults with focal-onset seizures, one open-label safety trial, and a variety of published abstract material that provided additional post hoc data.Expert opinion: In two placebo-controlled randomized multicenter phase 2 trials adjunct CNB showed unusually high efficacy with rates of seizure-free people with epilepsy (PWE) partially beyond 20%. However, during the clinical program cases of drug-related reactions with eosinophilia and systemic symptoms (DRESS syndrome) occurred. Therefore, an open-label safety study was performed in more than 1300 PWE with particularly slower titration schedules which did not add more cases with similar reactions. Taking into consideration the promising efficacy and the safety experience from the open-label trial, CNB applied according to the meanwhile recommended titration strategy, might offer a new prospect.

Qualification and application of liquid chromatography-quadrupole time-of-flight mass spectrometric method for the determination of carisbamate in rat plasma and prediction of its human pharmacokinetics using physiologically based pharmacokinetic modeling

Carisbamate is an antiepileptic drug and it also has broad neuroprotective activity and anticonvulsant reaction. In this study, a liquid chromatography-quadrupole time-of-flight mass spectrometric (LC-qTOF-MS) method was developed and applied for the determination of carisbamate in rat plasma to support in vitro and in vivo studies. A quadratic regression (weighted 1/concentration²), with an equation y = ax² + bx + c, was used to fit calibration curves over the concentration range from 9.05 to 6,600 ng/mL for carisbamate in rat plasma. Preclinical in vitro and in vivo studies of carisbamate have been studied through the developed bioanalytical method. Based on these study results, human pharmacokinetic (PK) profile has been predicted using physiologically based pharmacokinetic (PBPK) modeling. The PBPK model was optimized and validated by using the in vitro and in vivo data. The human PK of carisbamate after oral dosing of 750 mg was simulated by using this validated PBPK model. The human PK parameters and profiles predicted from the validated PBPK model were similar to the clinical data. This PBPK model developed from the preclinical data for carisbamate would be useful for predicting the PK of carisbamate in various clinical settings.

[Cenobamate-a new perspective for epilepsy treatment]

In spite of the introduction of numerous new antiseizure drugs (ASD) over the last decades, the percentage of drug-resistant epilepsies has remained almost stable. To achieve seizure freedom in such patients with any modified ASD regimen is an exception. Cenobamate (CNB) is a new ASD that showed unusually high efficacy in the pivotal placebo controlled, randomized trials. In both studies (C013 and C017), the rate of seizure-free patients was sometimes more than 20% and thus in a range never reached over the last decades in comparable trials with other new ASDs. This suggests that CNB which is already approved in the USA might actually offer a new and encouraging perspective for epilepsy treatment concerning efficacy. In this review the pharmacological profile, the currently known mode of action, and the results of the clinical trials are summarized.

Modeling epileptic spasms during infancy: Are we heading for the treatment yet?

Infantile spasms (IS or epileptic spasms during infancy) were first described by Dr. William James West (aka West syndrome) in his own son in 1841. While rare by definition (occurring in 1 per 3200-3400 live births), IS represent a major social and treatment burden. The etiology of IS varies - there are many (>200) different known pathologies resulting in IS and still in about one third of cases there is no obvious reason. With the advancement of genetic analysis, role of certain genes (such as ARX or CDKL5 and others) in IS appears to be important. Current treatment strategies with incomplete efficacy and serious potential adverse effects include adrenocorticotropin (ACTH), corticosteroids (prednisone, prednisolone) and vigabatrin, more recently also a combination of hormones and vigabatrin. Second line treatments include pyridoxine (vitamin B6) and ketogenic diet. Additional treatment approaches use rapamycin, cannabidiol, valproic acid and other anti-seizure medications. Efficacy of these second line medications is variable but usually inferior to hormonal treatments and vigabatrin. Thus, new and effective models of this devastating condition are required for the search of additional treatment options as well as for better understanding the mechanisms of IS. Currently, eight models of IS are reviewed along with the ideas and mechanisms behind these models, drugs tested using the models and their efficacy and usefulness. Etiological variety of IS is somewhat reflected in the variety of the models. However, it seems that for finding precise personalized approaches, this variety is necessary as there is no "one-size-fits-all" approach possible for both IS in particular and epilepsy in general.

The safety of medications used to treat peripheral neuropathic pain, part 1 (antidepressants and antiepileptics): review of double-blind, placebo-controlled, randomized clinical trials

INTRODUCTION

Peripheral neuropathic pain is a highly disabling condition for patients and a challenge for neurologists and pain physicians. Although many drugs have been assessed in scientific studies, few have demonstrated a clear clinical efficacy against neuropathic pain. Moreover, the paucity of data regarding their safety raised the question on the benefit-risk ratio when used in patients experiencing peripheral neuropathies.

AREAS COVERED

The authors conducted a review of double-blind, placebo-controlled, randomized clinical trials to assess the safety of medications used to treat neuropathic pain. This first review was focused on antidepressant and antiepileptic medications. The aim was to provide an overview of the treatment-emergent adverse events (≥10%) and the serious adverse effects described in clinical trials.

EXPERT OPINION

Among antiepileptics and antidepressants, duloxetine appeared to have the most detailed safety for the treatment of peripheral neuropathic pain. Over all studies, the most commonly reported adverse effects were dizziness, drowsiness, nausea, and constipation. Only 20.0% of the included studies (N = 90) presented a good description of adverse effects that included a statistical comparison vers usa placebo group. Important methodological improvements must be made to improve the assessment of medication safety in future clinical trials.

Do neurologists around the world agree when diagnosing epilepsy? - Results of an international EpiNet study

OBJECTIVE

Previous studies have shown moderate agreement between physicians when diagnosing epilepsy, but have included small numbers. The EpiNet study group was established to undertake multicentre clinical trials in epilepsy. Before commencing trials, we wanted to determine levels of agreement between physicians from different countries and different health systems when diagnosing epilepsy, specific seizure types and etiologies.

METHODS

30 Case scenarios describing six children and 24 adults with paroxysmal events (21 epileptic seizures, nine non-epileptic attacks) were presented to physicians with an interest in epilepsy. Physicians were asked how likely was a diagnosis of epilepsy; if seizures were generalised or focal; and the likely etiology. For 23 cases, clinical information was presented in Step 1, and investigations in Step 2.

RESULTS

189 Participants from 36 countries completed the 30 cases. Levels of agreement were determined for 154 participants who provided details regarding their clinical experience. There was substantial agreement for diagnosis of epilepsy (kappa=0.61); agreement was fair to moderate for seizure type(s) (kappa=0.40) and etiology (kappa=0.41). For 23 cases with two steps, agreement increased from step 1 to step 2 for diagnosis of epilepsy (kappa 0.56-0.70), seizure type(s) (kappa 0.38-0.52), and etiology (kappa 0.38-0.47). Agreement was better for 53 epileptologists (diagnosis of epilepsy, kappa=0.66) than 56 neurologists with a special interest in epilepsy (kappa=0.58). Levels of agreement differed slightly between physicians practicing in different parts of the world, between child and adult neurologists, and according to one's experience with epilepsy.

CONCLUSION

Although there is substantial agreement when epileptologists diagnose epilepsy, there is less agreement for diagnoses of seizure types and etiology. Further education of physicians regarding semiology of different seizure types is required. Differences in approach to diagnosis, both between physicians and between countries, could impact negatively on clinical trials of anti-epileptic drugs.

Carisbamate blockade of T-type voltage-gated calcium channels

OBJECTIVES

Carisbamate (CRS) is a novel monocarbamate compound that possesses antiseizure and neuroprotective properties. However, the mechanisms underlying these actions remain unclear. Here, we tested both direct and indirect effects of CRS on several cellular systems that regulate intracellular calcium concentration [Ca²⁺ ]_i .

METHODS

We used a combination of cellular electrophysiologic techniques, as well as cell viability, Store Overload-Induced Calcium Release (SOICR), and mitochondrial functional assays to determine whether CRS might affect [Ca²⁺ ]_i levels through actions on the endoplasmic reticulum (ER), mitochondria, and/or T-type voltage-gated Ca²⁺ channels.

RESULTS

In CA3 pyramidal neurons, kainic acid induced significant elevations in [Ca²⁺ ]_i and long-lasting neuronal hyperexcitability, both of which were reversed in a dose-dependent manner by CRS. Similarly, CRS suppressed spontaneous rhythmic epileptiform activity in hippocampal slices exposed to zero-Mg²⁺ or 4-aminopyridine. Treatment with CRS also protected murine hippocampal HT-22 cells against excitotoxic injury with glutamate, and this was accompanied by a reduction in [Ca²⁺ ]_i . Neither kainic acid nor CRS alone altered the mitochondrial membrane potential (ΔΨ) in intact, acutely isolated mitochondria. In addition, CRS did not affect mitochondrial respiratory chain activity, Ca²⁺ -induced mitochondrial permeability transition, and Ca²⁺ release from the ER. However, CRS significantly decreased Ca²⁺ flux in human embryonic kidney tsA-201 cells transfected with Ca_v 3.1 (voltage-dependent T-type Ca²⁺ ) channels.

SIGNIFICANCE

Our data indicate that the neuroprotective and antiseizure activity of CRS likely results in part from decreased [Ca²⁺ ]_i accumulation through blockade of T-type Ca²⁺ channels.

Antiepileptic drugs in development pipeline: A recent update

Epilepsy is the most common neurological disorder which significantly affects the quality of life and poses a health as well as economic burden on society. Epilepsy affects approximately 70 million people in the world. The present article reviews the scientific rationale, brief pathophysiology of epilepsy and newer antiepileptic drugs which are presently under clinical development. We have searched the investigational drugs using the key words ‘antiepileptic drugs,’ ‘epilepsy,’ ‘Phase I,’ ‘Phase II’ and ‘Phase III’ in American clinical trial registers (clinicaltrials.gov), the relevant published articles using National Library of Medicine's PubMed database, company websites and supplemented results with a manual search of cross-references and conference abstracts. This review provides a brief description about the antiepileptic drugs which are targeting different mechanisms and the clinical development status of these drugs. Besides the presence of old as well as new AEDs, still there is a need of new drugs or the modified version of old drugs in order to make affected people free of seizures. An optimistic approach should be used to translate the success of preclinical testing to clinical practice. There is an urgent need to improve animal models and to explore new targets with better understanding in order to develop the novel drugs with more efficacy and safety.

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This review primarily focused on antiepileptic drugs under clinical development.

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The more realistic approach is needed to discover and develop the novel antiepileptic drugs.

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Modification of conventional drugs or search of newer targets can lead to development of promising antiepileptic drugs.

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To develop more efficacious and safe drugs for treatment of epilepsy and refractory seizures

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There are a number of novel antiepileptic compounds which are under various stages of drug development.

The anticonvulsant actions of carisbamate associate with alterations in astrocyte glutamine metabolism in the lithium-pilocarpine epilepsy model

As reported previously, in the lithium-pilocarpine model of temporal lobe epilepsy (TLE), carisbamate (CRS) produces strong neuroprotection, leads to milder absence-like seizures, and prevents behavioral impairments in a subpopulation of rats. To understand the metabolic basis of these effects, here we injected 90 mg/kg CRS or vehicle twice daily for 7 days starting 1 h after status epilepticus (SE) induction in rats. Two months later, we injected [1-¹³ C]glucose and [1,2-¹³ C]acetate followed by head microwave fixation after 15 min. ¹³ C incorporation into metabolites was analyzed using ¹³ C magnetic resonance spectroscopy. We found that SE reduced neuronal mitochondrial metabolism in the absence but not in the presence of CRS. Reduction in glutamate level was prevented by CRS and aspartate levels were similar to controls only in rats displaying absence-like seizures after treatment [CRS-absence-like epilepsy (ALE)]. Glutamine levels in CRS-ALE rats were higher compared to controls in hippocampal formation and limbic structures while unchanged in rats displaying motor spontaneous recurrent seizures after treatment (CRS-TLE). Astrocytic mitochondrial metabolism was reduced in CRS-TLE, and either enhanced or unaffected in CRS-ALE rats, which did not affect the transfer of glutamine from astrocytes to neurons. In conclusion, CRS prevents reduction in neuronal mitochondrial metabolism but its effect on astrocytes is likely key in determining outcome of treatment in this model. To understand the metabolic basis of the strong neuroprotection and reduction in seizure severity caused by carisbamate (CRS) in the lithium-pilocarpine (Li-Pilo) model of temporal lobe epilepsy (TLE), we injected CRS for 7 days starting 1 h after status epilepticus and 2 months later [1-¹³ C]glucose and [1,2-¹³ C]acetate. ¹³ C Magnetic resonance spectroscopy analysis was performed on brain extracts and we found that CRS prevented reduction in neuronal mitochondrial metabolism but its effect on astrocytes was likely key in determining outcome of treatment in this model. ALE = absence like epilepsy; acetyl CoA = acetyl coenzyme A; GS = glutamine synthetase; PAG = phosphate activated glutaminase; PC = pyruvate carboxylase; OAA = oxaloacetate; TCA cycle = tricarboxylic acid cycle.

Pharmacotherapy for tonic-clonic seizures

INTRODUCTION

Occurrence of generalized tonic-clonic seizures (GTCS) is one of the most important risk factors of seizure-related complications and comorbidities in patients with epilepsy. Their prevention is therefore an important aspect of therapeutic management both in idiopathic generalized epilepsies and in focal epilepsies.

AREAS COVERED

It has been shown that the efficacy of antiepileptic drugs (AEDs) varies across epilepsy syndromes, with some AEDs efficacious against focal seizures with secondary GTCS (sGTCS) but aggravating primary GTCS (pGTCS). In patients with pGTCS, evidence-based data support the preferential use of valproic acid, lamotrigine, levetiracetam and topiramate. In patients with sGTCS, all AEDs approved in the treatment of focal epilepsies might be used.

EXPERT OPINION

Both in pGTCS and sGTCS, additional data are required, specifically to inform about the relative efficacy of AEDs in relation to each other. Although valproic acid might be the most efficacious drug in idiopathic generalized epilepsies, it should be avoided in women of childbearing age due to its safety profile. In patients with sGTCS, AEDs for which the impact on this seizure type has been formally evaluated and which have demonstrated greater efficacy than placebo might preferentially be used, such as lacosamide, perampanel and topiramate.

Network meta-analyses of antiepileptic drug efficacy and tolerability in drug-resistant focal epilepsies: a clinical perspective

PURPOSE

Network meta-analysis (NMA) is a new technique that allows multiple treatment comparisons and provides estimates of effect sizes for all possible pair-wise comparisons. Several NMAs of antiepileptic drug (AED) efficacy and tolerability in individuals with refractory focal epilepsy, however, came to non-specific and, in some cases, divergent conclusions. We review some clinical factors that may be responsible for these inconsistent findings.

RESULTS

A major issue is the small number of individuals included in the meta-analyses with consequent wide confidence intervals and lack of ability to achieve significant results. Further issues are lack of robustness of the measured efficacy outcome-the responder ratio (the percentage of individuals with a >50 % improvement in seizure frequency); the selection of randomized studies (RCTs) included, i.e., the inclusion of studies with heterogeneous populations (children and adults); and inclusion of people treated with different doses of the experimental drug. Some methods of analysing data from RCTs, such as the last observation carried forward (LOCF) analysis, the choice of different phases of the study to compare to baseline, and the year in which the trial was conducted, selectively affect measurement of efficacy outcomes. Titration speed and other methodological aspects selectively affect tolerability.

CONCLUSION

Several factors restrict the analysis of clinically useful estimates of the comparative efficacy of AEDs, while analysis of tolerability may be easier to accomplish.

Brivaracetam as adjunctive treatment for uncontrolled partial epilepsy in adults: a phase III randomized, double-blind, placebo-controlled trial

PURPOSE

Brivaracetam (BRV) is a novel high-affinity synaptic vesicle protein 2A ligand currently being investigated for the treatment of epilepsy. The purpose of this phase III study was to evaluate the efficacy and safety/tolerability of adjunctive BRV in adults with uncontrolled partial-onset (focal) seizures.

METHODS

This was a prospective, multicenter, randomized, double-blind, placebo-controlled, parallel-group, fixed-dose trial (N01253; NCT00464269). Adults aged 16-70 years with well-characterized partial epilepsy not fully controlled despite treatment with one or two antiepileptic drugs (AEDs) were enrolled. Patients who experienced eight or more partial-onset seizures, whether or not secondarily generalized, during the 8-week prospective baseline period were randomized (1:1:1:1) to receive twice-daily placebo (PBO) or BRV (5, 20, or 50 mg/day) without titration. The primary efficacy endpoint was percent reduction over PBO in baseline-adjusted partial-onset seizure frequency/week during the 12-week treatment period. Comparison of BRV with PBO was sequential (50, 20 mg/day, then 5 mg/day). Secondary endpoints included ≥50% responder rate and median percent reduction from baseline in partial-onset seizure frequency/week. Post hoc analyses included the primary efficacy endpoint evaluated over 28 days and exploratory subanalyses of efficacy by seizure subtype. Safety and tolerability assessments included treatment-emergent adverse events (TEAEs), laboratory tests, electrocardiography, vital signs, and physical and neurologic examinations.

KEY FINDINGS

Of 400 patients randomized, 396 were included in the intent-to-treat (ITT) population (PBO n = 98, BRV 5 mg/day n = 97, BRV 20 mg/day n = 100, BRV 50 mg/day n = 101) and 392 comprised the modified ITT (mITT) population. A total of 361 (91.2%) of 396 patients completed the study. Most patients (78.3%) were receiving two concomitant AEDs. Percent reduction in partial-onset seizure frequency/week over PBO was -0.9% (p = 0.885) for BRV 5 mg/day, 4.1% (p = 0.492) for BRV 20 mg/day, and 12.8% (p = 0.025) for BRV 50 mg/day (mITT population). Statistical significance was also achieved for the percent reduction over PBO in baseline-adjusted partial-onset seizure frequency/28 days for BRV 50 mg/day (22.0%; p = 0.004) but not for the other BRV dose groups. In the BRV 50 mg/day group, statistical significance was also seen for the ≥50% responder rate (BRV 32.7% vs. PBO 16.7%; p = 0.008) and median percent reduction from baseline in partial-onset seizure frequency/week (BRV 30.5% vs. PBO 17.8%; p = 0.003). In the exploratory subanalysis by seizure subtype, median percent reduction from baseline in seizure frequency/week and ≥50% responder rate were numerically greater than PBO in the BRV 20 and 50 mg/day groups for simple partial, complex partial, and secondarily generalized seizures. BRV was generally well tolerated, with the majority of TEAEs being mild-to-moderate in intensity. Of the TEAEs reported by ≥5% patients, those with a frequency >3% higher than PBO for any dose of BRV compared with PBO were somnolence, dizziness, fatigue, influenza, insomnia, nasopharyngitis, vomiting, diarrhea, urinary tract infection, and nausea.

SIGNIFICANCE

Adjunctive BRV at a daily dose of 50 mg was associated with statistically significant reductions in seizure frequency compared with PBO. All doses of BRV showed good tolerability throughout the study.

Efficacy and safety of carisbamate in patients with diabetic neuropathy or postherpetic neuralgia: results from 3 randomized, double-blind placebo-controlled trials

The results of 3 proof-of-concept studies to evaluate carisbamate's efficacy and safety in treating neuropathic pain are presented. In studies 1 (postherpetic neuralgia, n = 91) and 2 (diabetic neuropathy, n = 137), patients received carisbamate 400 mg/day or placebo for 4 weeks and then crossed over to the other treatment for 4 weeks. In study 3 (diabetic neuropathy, higher carisbamate doses), patients (n = 386) were randomized (1:1:1:1) to receive either carisbamate 800 mg/day, 1200 mg/day, pregabalin 300 mg/day or placebo for 15 weeks. Primary efficacy end point was the mean of the last 7 average daily pain scores obtained on days the study drug was taken, for all 3 studies. Least square mean (95% CI) differences between carisbamate and placebo groups on the primary end point were as follows: study 1: -0.512 (-1.32, 0.29) carisbamate 400 mg/day; study 2: -0.307 (-0.94, 0.33) carisbamate 400 mg/day; and study 3: -0.51 (-1.10, 0.08), carisbamate 800 mg/day; -0.55 (-1.13, 0.04), carisbamate 1200 mg/day; and -0.43 (-1.01, 0.15), pregabalin 300 mg/day. Neither carisbamate (all 3 studies) nor pregabalin (study 3) significantly differed from placebo, although multiple secondary end points showed significant improvement in efficacy with carisbamate in studies 1 and 2. Dizziness was the only treatment-emergent adverse event occurring at ≥10% difference in carisbamate groups versus placebo (study 1: 12% vs. 1%; study 3: 14% vs. 4%; study 2: 1% vs. 2%). Carisbamate, although well tolerated, did not demonstrate efficacy in neuropathic pain across these studies, nor did the active comparator pregabalin (study 3).

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.

Effect of carisbamate on the pharmacokinetics and pharmacodynamics of warfarin in healthy participants

Carisbamate's effect (200 mg twice-daily [study 1], 600 mg twice-daily [study 2]) on warfarin's (25 mg single dose) pharmacokinetics and pharmacodynamics (international normalized ratio) was assessed during 2 open-label studies in healthy participants. Coadministration of either carisbamate regimen produced small changes on the mean maximum plasma concentration (C(max)) and mean area under the plasma concentration-time curve to the last measurable time point (AUC(last)) of (S)- and (R)-warfarin, which are unlikely to be clinically significant. For (S)-warfarin, the ratios (with carisbamate/without carisbamate) of geometric means for C(max) were 105.44 (study 1) and 98.48 (study 2) and for AUC(last) were 109.33 (study 1) and 114.43 (study 2); the corresponding 90% confidence intervals were within the bioequivalence limits of 80% to 125%. Results were similar for (R)-warfarin. Carisbamate at 600 mg (but not 200 mg) twice-daily prolonged the elimination half-life of (S)- and (R)-warfarin by ~10 hours (25% and 32% increase, respectively). Prothrombin time was unaltered by either carisbamate dose. Adverse events with the highest incidence were dizziness (50%) and headache (50%) in study 1 and somnolence (56%) in study 2. Warfarin exposure and international normalized ratio were unaffected by coadministration of carisbamate 200 mg or 600 mg twice-daily. Carisbamate was well tolerated.

Cognitive effects of carisbamate in randomized, placebo-controlled, healthy-volunteer, multidose studies

Adverse cognitive effects are an important concern for drugs that influence the central nervous system. Carisbamate is a novel drug in development for treatment of seizures and neuropathic pain. Information on its cognitive effects is limited. Three controlled, multiple-dose, crossover studies with treatment durations of 5-9 days were designed to examine the cognitive effects of carisbamate on healthy volunteers. In one study, apparent dose-dependent effects on response, vigilance, and recognition speed were observed (1000 mg and 1500 mg/day). Carisbamate did not differ from placebo for most variables in the other two studies, but increased reaction time and reduced Sternberg memory were seen at higher dosages. Carisbamate did not produce clinically significant adverse effects on cognitive performance at doses <1000 mg/day. Effects were mild to modest at the higher doses tested.

Carisbamate acutely suppresses spasms in a rat model of symptomatic infantile spasms

PURPOSE

Infantile spasms are the signature seizures of West syndrome. The conventional treatments for infantile spasms, such as adrenocorticotropic hormone (ACTH) and vigabatrin, are not always effective, especially in symptomatic infantile spasms (SIS). We tested the efficacy of carisbamate, a novel neurotherapeutic drug, to suppress spasms in the multiple-hit rat model of SIS, and compared it with phenytoin to determine if its effect is via sodium-channel blockade.

METHODS

Sprague-Dawley rats received right intracerebral infusions of doxorubicin and lipopolysaccharide at postnatal day 3 (PN3) and intraperitoneal p-chlorophenylalanine at PN5. A single intraperitoneal injection of carisbamate was administered at PN4, after the onset of spasms, at the following doses: 10 mg/kg (CRS-10), 30 mg/kg (CRS-30), and 60 mg/kg (CRS-60), and was compared to vehicle-injected group (VEH). Video-monitoring of PN6-7 CRS-60 or VEH-injected pups was also done.

KEY FINDINGS

Carisbamate acutely reduced both behavioral spasms (CRS-30 and CRS-60 groups only) and electroclinical spasms during the first 2-3 postinjection hours, without detectable toxicity or mortality. In contrast, phenytoin (20 or 50 mg/kg) failed to suppress spasms.

SIGNIFICANCE

Our findings provide preclinical evidence that carisbamate displays acute anticonvulsive effect on spasms through a sodium channel-independent mechanism. Because spasms in the multiple-hit rat model are refractory to ACTH and transiently sensitive to vigabatrin, carisbamate may constitute a candidate new therapy for SIS, including the ACTH-refractory spasms. Further confirmation with clinical studies is needed.

Carisbamate has powerful disease-modifying effects in the lithium-pilocarpine model of temporal lobe epilepsy

Lithium-pilocarpine, a relevant model of temporal lobe epilepsy was used to test the neuroprotective and antiepileptogenic effects of carisbamate. Status epilepticus (SE) was induced in adult rats by lithium and pilocarpine. Carisbamate (30, 60, 90, and 120 mg/kg) was injected at 1 and 9 h after SE onset and continued twice daily for 6 additional days. The reference groups received diazepam instead of carisbamate. Neuroprotection was assessed during the first 24 h of SE with Fluoro-Jade B and after 14 days with thionine staining. SE severity and epileptic outcome were assessed by video, and surface and depth electroencephalographic recordings. At the two highest doses, carisbamate treatment reduced SE severity; produced strong neuroprotection of hippocampus, ventral cortices, thalamus, and amygdala; prevented mossy fiber sprouting in the dentate gyrus of the hippocampus; and delayed or suppressed the occurrence of spontaneous motor seizures. Rats with no spontaneous motor seizures displayed spike-and-wave discharges that share all the characteristics of absence seizures. In conclusion, carisbamate is able to induce strong neuroprotection and affect the nature of epileptogenic events occurring during and after lithium-pilocarpine status epilepticus, reflecting marked insult- and disease-modifying effects.

Antiepileptic and antiepileptogenic performance of carisbamate after head injury in the rat: blind and randomized studies

Carisbamate (CRS) exhibits broad acute anticonvulsant activity in conventional anticonvulsant screens, genetic models of absence epilepsy and audiogenic seizures, and chronic spontaneous motor seizures arising after chemoconvulsant-induced status epilepticus. In add-on phase III trials with pharmacoresistant patients CRS induced < 30% average decreases in partial-onset seizure frequency. We assessed the antiepileptogenic and antiepileptic performance of subchronic CRS administration on posttraumatic epilepsy (PTE) induced by rostral parasaggital fluid percussion injury (rpFPI), which closely replicates human contusive closed head injury. Studies were blind and randomized, and treatment effects were assessed on the basis of sensitive electrocorticography (ECoG) recordings. Antiepileptogenic effects were assessed in independent groups of control and CRS-treated rats, at 1 and 3 months postinjury, after completion of a 2-week prophylactic treatment initiated 15 min after injury. The antiepileptic effects of 1-week CRS treatments were assessed in repeated measures experiments at 1 and 4 months postinjury. The studies were powered to detect ~50 and ~40% decreases in epilepsy incidence and frequency of seizures, respectively. Drug/vehicle treatment, ECoG analysis, and [CRS](plasma) determination all were performed blind. We detected no antiepileptogenic and an equivocal transient antiepileptic effects of CRS despite [CRS](plasma) comparable with or higher than levels attained in previous preclinical and clinical studies. These findings contrast with previous preclinical data demonstrating large efficacy of CRS, but agree with the average effect of CRS seen in clinical trials. The data support the use of rpFPI-induced PTE in the adolescent rat as a model of pharmacoresistant epilepsy for preclinical development.