Clinical trials for therapeutic assessment of antiepileptic drugs in the 21st century: obstacles and solutions

Transition behavior of the seizure dynamics modulated by the astrocyte inositol triphosphate noise

Epilepsy is a neurological disorder with recurrent seizures, which convey complex dynamical characteristics including chaos and randomness. Until now, the underlying mechanism has not been fully elucidated, especially the bistable property beneath the epileptic random induction phenomena in certain conditions. Inspired by the recent finding that astrocyte GTPase-activating protein (G-protein)-coupled receptors could be involved in stochastic epileptic seizures, we proposed a neuron-astrocyte network model, incorporating the noise of the astrocytic second messenger, inositol triphosphate (IP3) that is modulated by G-protein-coupled receptor activation. Based on this model, we have statistically analyzed the transitions of epileptic seizures by performing repeatable simulation trials. Our simulation results show that the increase in the IP3 noise intensity induces depolarization-block epileptic seizures together with an increase in neuronal firing frequency, consistent with corresponding experiments. Meanwhile, the bistable states of the seizure dynamics were present under certain noise intensities, during which the neuronal firing pattern switches between regular sparse spiking and epileptic seizure states. This random presence of epileptic seizures is absent when the noise intensity continues to increase, accompanying with an increase in the epileptic depolarization block duration. The simulation results also shed light on the fact that calcium signals in astrocytes play significant roles in the pattern formations of the epileptic seizure. Our results provide a potential pathway for understanding the epileptic randomness in certain conditions.

Clinical Trial Design for Disease-Modifying Therapies for Genetic Epilepsies

Although trials with anti-seizure medications (ASMs) have not shown clear anti-epileptogenic or disease-modifying activity in humans to date, rapid advancements in genomic technology and emerging gene-mediated and gene replacement options offer hope for the successful development of disease-modifying therapies (DMTs) for genetic epilepsies. In fact, more than 26 potential DMTs are in various stages of preclinical and/or clinical development for genetic syndromes associated with epilepsy. The scope of disease-modification includes but is not limited to effects on the underlying pathophysiology, the condition's natural history, epilepsy severity, developmental achievement, function, behavior, sleep, and quality of life. While conventional regulatory clinical trials for epilepsy therapeutics have historically focused on seizure reduction, similarly designed trials may prove ill-equipped to identify these broader disease-modifying benefits. As we look forward to this pipeline of DMTs, focused consideration should be given to the challenges they pose to conventional clinical trial designs for epilepsy therapeutics. Just as DMTs promise to fundamentally alter how we approach the care of patients with genetic epilepsy syndromes, DMTs likewise challenge how we traditionally construct and measure the success of clinical trials. In the following, we briefly review the historical and preclinical frameworks for DMT development for genetic epilepsies and explore the many novel challenges posed for such trials, including the choice of suitable outcome measures, trial structure, timing and duration of treatment, feasible follow-up period, varying safety profile, and ethical concerns.

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.

Methodological issues associated with clinical trials in epilepsy

INTRODUCTION

despite methodological advances in epilepsy clinical trials, the proportion of patients reaching seizure-freedom has not substantially changed over the years. We review the main methodological limitations of current trials, the possible strategies to overcome these limits, and the issues that need to be addressed in next future. Area covered: references were identified by PubMed search until March 2017 and unpublished literature was searched on ClinicalTrials.gov. Add-on trials mainly involve refractory epilepsy subjects, reducing overall response to the investigational drug. The inclusion of subjects with earlier disease from less developed countries has partially allowed overcoming this limitation, but has introduced more random variability of results. Monotherapy trials rise methodological, economical, and ethical concerns with different regulatory requirements in European Union and in the United States of America. Newer trial designs, such as futility trials or 'time-to-event' design, have been implemented. Moreover, both add-on and monotherapy trials results might be affected by patient's ability to recognize and record seizures, and by randomness of seizures occurrence over time. Possible strategies to achieve more reliable outcomes are detailed. Expert commentary: clinical trial methodology needs to be optimized to better address regulatory agencies requirements and to encounter both patients' and clinicians' needs.

Can Matching-Adjusted Indirect Comparison Methods Mitigate Placebo Response Differences Among Patient Populations in Adjunctive Trials of Brivaracetam and Levetiracetam?

BACKGROUND AND OBJECTIVE

Patients with focal seizures recruited into adjunctive antiepileptic drug (AED) trials have become more refractory and severe over time; concurrently, placebo responses have increased. To attempt to account for heterogeneity among trials, propensity-score weighted patient-level data were used to indirectly compare placebo responses reported in brivaracetam and levetiracetam trials.

METHODS

Patient-level data from randomised, placebo-controlled brivaracetam (recruited 2007-2014) and levetiracetam (1993-1998) trials were pooled. Consistent inclusion/exclusion criteria were applied and outcomes were defined consistently. Potentially confounding baseline characteristics were adjusted for using propensity score weighting. Weighting success was assessed using placebo response.

RESULTS

In total, 707 and 473 active drug and 399 and 253 placebo patients comprised the brivaracetam and levetiracetam groups, respectively. Before weighting, several baseline variables were significantly different between groups; after weighting, prior vagal nerve stimulation, co-morbid depression and co-morbid anxiety remained different. Before weighting, median seizure frequency reduction was 21.7 and 3.9% in the brivaracetam and levetiracetam placebo arms, respectively; after weighting, median reduction was 15.0 and 6.0%. The comparison of non-randomised groups could be biased by unobserved confounding factors and region of residence. Lifetime AED history was unavailable in the brivaracetam trials and excluded from analysis.

CONCLUSIONS

Placebo responses remained different between brivaracetam and levetiracetam trials after propensity score weighting, indicating the presence of residual confounding factors associated with placebo response in these trials. It therefore remains problematic to conduct reliable indirect comparisons of brivaracetam and levetiracetam given the current evidence base, which may apply to comparisons between other AED trials.

Adjunctive pregabalin vs gabapentin for focal seizures: Interpretation of comparative outcomes

Objective:

To evaluate the comparative safety and adjunctive efficacy of pregabalin and gabapentin in reducing seizure frequency in patients with partial-onset seizures based on prestudy modeling showing superior efficacy for pregabalin.

Methods:

The design of this comparative efficacy and safety study of pregabalin and gabapentin as adjunctive treatment in adults with refractory partial-onset seizures was randomized, flexible dose, double blind, and parallel group. The study included a 6-week baseline and a 21-week treatment phase. The primary endpoint was the percentage change from baseline in 28-day seizure rate to the treatment phase.

Results:

A total of 484 patients were randomized to pregabalin (n = 242) or gabapentin (n = 242). Of these, 359 patients (187 pregabalin, 172 gabapentin) completed the treatment phase. The observed median and mean in percentage change from baseline was −58.65 and −47.7 (SD 48.3) for pregabalin and −57.43 and −45.28 (SD 60.6) for gabapentin. For the primary endpoint, there was no significant difference between treatments. The Hodges-Lehman estimated median difference was 0.0 (95% confidence interval −6.0 to 7.0). Safety profiles were comparable and consistent with prior trials.

Conclusions:

The absence of the anticipated efficacy difference based on modeling of prior, nearly identical trials and the larger-than-expected response rates of the 2 antiepileptic drugs were unexpected. These findings raise questions that are potentially important to consider in future comparative efficacy trials.

ClinicalTrials.gov identifier:

NCT00537940.

Classification of evidence:

This study provides Class II evidence that for patients with partial seizures enrolled in this study, pregabalin is not superior to gabapentin in reducing seizure frequency. Because of the atypical response rates, the results of this study are poorly generalizable to other epilepsy populations.

Fit for purpose application of currently existing animal models in the discovery of novel epilepsy therapies

Animal seizure and epilepsy models continue to play an important role in the early discovery of new therapies for the symptomatic treatment of epilepsy. Since 1937, with the discovery of phenytoin, almost all anti-seizure drugs (ASDs) have been identified by their effects in animal models, and millions of patients world-wide have benefited from the successful translation of animal data into the clinic. However, several unmet clinical needs remain, including resistance to ASDs in about 30% of patients with epilepsy, adverse effects of ASDs that can reduce quality of life, and the lack of treatments that can prevent development of epilepsy in patients at risk following brain injury. The aim of this review is to critically discuss the translational value of currently used animal models of seizures and epilepsy, particularly what animal models can tell us about epilepsy therapies in patients and which limitations exist. Principles of translational medicine will be used for this discussion. An essential requirement for translational medicine to improve success in drug development is the availability of animal models with high predictive validity for a therapeutic drug response. For this requirement, the model, by definition, does not need to be a perfect replication of the clinical condition, but it is important that the validation provided for a given model is fit for purpose. The present review should guide researchers in both academia and industry what can and cannot be expected from animal models in preclinical development of epilepsy therapies, which models are best suited for which purpose, and for which aspects suitable models are as yet not available. Overall further development is needed to improve and validate animal models for the diverse areas in epilepsy research where suitable fit for purpose models are urgently needed in the search for more effective treatments.

Response to placebo in clinical epilepsy trials--Old ideas and new insights

Randomized placebo-controlled trials are a mainstay of modern clinical epilepsy research; the success or failure of innovative therapies depends on proving superiority to a placebo. Consequently, understanding what drives response to placebo (including the "placebo effect") may facilitate evaluation of new therapies. In this review, part one will explore observations about placebos specific to epilepsy, including the relatively higher placebo response in children, apparent increase in placebo response over the past several decades, geographic variation in placebo effect, relationship to baseline epilepsy characteristics, influence of nocebo on clinical trials, the possible increase in (SUDEP) in placebo arms of trials, and patterns that placebo responses appear to follow in individual patients. Part two will discuss the principal causes of placebo responses, including regression to the mean, anticipation, classical conditioning, the Hawthorne effect, expectations from symbols, and the natural history of disease. Included in part two will be a brief overview of recent advances using simulations from large datasets that have afforded new insights into causes of epilepsy-related placebo responses. In part three, new developments in study design will be explored, including sequential parallel comparison, two-way enriched design, time to pre-randomization, delayed start, and cohort reduction techniques.

Prevention of generalized tonic-clonic seizures in refractory focal epilepsy: a meta-analysis

OBJECTIVES

Secondary generalized tonic-clonic seizures (SGTCS) are among the most severe forms of seizures, and the main risk factor for sudden unexpected death in epilepsy (SUDEP). Whether some antiepileptic drugs (AEDs) might be more efficacious than others on SGTCS in patients with drug-resistant focal epilepsy thus represents an important clinical issue for which no data are currently available.

METHODS

We performed a meta-analysis of randomized controlled trials of adjunctive AED in which information on efficacy outcomes (i.e., responder rate and/or frequency per 28 days relative to baseline) were available both for all seizure types and for SGTCS. The primary analysis evaluated the efficacy of AEDs on all types of seizure and on SGTCS by comparing the responder rates for AED and for placebo.

RESULTS

Responder rate was available both for all seizure types and for SGTCS in 13 of the 72 eligible trials, evaluating 7 AEDs. Only three AEDs--lacosamide, perampanel and topiramate--showed greater efficacy than placebo. However, confidence intervals of relative risks overlapped for all AEDs but pregabalin, which demonstrated significantly lower efficacy than lacosamide, perampanel, and topiramate. Moreover, there was a nonsignificant trend toward a lower relative risk of responder rate for SGTCS than for all seizure types, which appeared related to a greater response to placebo for this outcome.

SIGNIFICANCE

Indirect comparison of AEDs using randomized placebo-controlled add-on trials does not support robust differences between AEDs to prevent SGTCS. Alternative designs for evaluation of therapeutic interventions in patients at risk for SGTCS-related complications are required.

Assessment of pharmacokinetics and tolerability of intranasal diazepam relative to rectal gel in healthy adults

Diazepam rectal gel (RG) is currently the only approved rescue therapy for outpatient management of seizure clusters in the United States. There is an unmet medical need for an alternative rescue therapy for seizure clusters that is effective, and more convenient to administer with a socially acceptable method of delivery. An intranasal diazepam formulation has been developed, and this study evaluates the tolerability and bioavailability of diazepam nasal spray (NS) relative to an equivalent dose of diazepam-RG in healthy adults. Twenty-four healthy adults were enrolled in a phase 1, open-label, 3-period crossover study. Plasma diazepam and metabolite concentrations were measured by serial sampling. Dose proportionality for 5- and 20-mg intranasal doses and the bioavailability of 20mg diazepam-NS relative to 20mg diazepam-RG were assessed by maximum plasma concentration (Cmax) and systemic exposure parameters (AUC0-∞ and AUC0-24). The mean Cmax values for 20mg diazepam-NS and 20mg diazepam-RG were 378 ± 106 and 328 ± 152 ng/mL, achieved at 1.0 and 1.5h, respectively. Subjects administered intranasal and rectal gel formulations experienced nasal and rectal leakage, respectively. Diazepam absorption following intranasal administration was consistent but 3 subjects with diazepam-RG had low plasma drug levels at the earliest assessment of 5 min, due to poor retention, and were excluded from analysis. Excluding them, the treatment ratios (20mg diazepam-NS:20mg diazepam-RG) and 90% confidence intervals for diazepam Cmax and AUC0-24 were 0.98 (0.85-1.14) and 0.89 (0.80-0.98), respectively, suggesting that the bioavailability was comparable between the two formulations. Dose proportionality was observed between the lowest and highest dose-strengths of intranasal formulation. Both intranasal and rectal treatments were well tolerated with mild to moderate adverse events. Results suggest that a single-dose of 20mg diazepam-NS is tolerable and comparable in bioavailability to that of diazepam-RG. The intranasal formulation may provide caregivers and patients with a more socially acceptable and convenient alternative rescue therapy in the acute treatment of seizure clusters.

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.

Anti-epileptogenic clinical trial designs in epilepsy: issues and options

Although trials with anti-seizure drugs have not shown anti-epileptogenic or disease-modifying activity in humans, new compounds are on the horizon that may require novel trial designs. We briefly discuss the unique challenges and the available options to identify innovative clinical trial designs that differentiate novel anti-epileptogenic and disease-modifying compounds, preferably early in phase II, from current anti-seizure drugs. The most important challenges of clinical testing of agents for epilepsy prevention include having sufficient preclinical evidence for a suitable agent to proceed with a human trial of an anti-epileptogenic drug, and to demonstrate the feasibility of doing such a trial. Major challenges in trial design to assess agents for disease modification include the choice of suitable study parameters, the identification of a high-risk study population, the type of control, the time and duration of treatment, and a feasible follow-up period.

Novel frontiers in epilepsy treatments: preventing epileptogenesis by targeting inflammation

Currently available epilepsy drugs only affect the symptoms (seizures), and there is a need for innovative treatments that target the underlying disease. Increasing evidence points to inflammation as a potentially important mechanism in epileptogenesis. In the last decade, a new generation of etiologically realistic syndrome-specific experimental models have been developed, which are expected to capture the epileptogenic mechanisms operating in corresponding patient populations, and to exhibit similar treatment responsiveness. Recently, an intervention known to have broad-ranging anti-inflammatory effects (selective brain cooling) has been found to prevent the development of spontaneously occurring seizures in an etiologically realistic rat model of post-traumatic epilepsy. Several drugs used clinically for other indications also have the potential for inhibiting inflammation, and should be investigated for antiepileptogenic activity in these models. If results of such studies are positive, these compounds could rapidly enter Phase III trials in patients at high risk of developing epilepsy.

Issues for new antiepilepsy drug development

PURPOSE OF REVIEW

Preclinical research in epileptology has been very successful in producing effective drugs. Unfortunately, however, seizures are still not adequately controlled in a third of the affected individuals, and comorbidities still impose a major burden on the quality of life. New preclinical and clinical drug development strategies are needed to identify drugs that target these unmet medical needs.

RECENT FINDINGS

Even in recent years, the antiseizure approach based on screenings has contributed to the identification of new drugs. Thus, it should not be abandoned. However, we propose that a radically new approach, specifically designed to tackle the existing gaps in care, should be developed to complement the traditional screening. This new approach will require integrated strategies for preclinical screening and experimental trial design. In this review, we will attempt to address some of the issues that must be resolved to engage this effort. Are there suitable models to tackle the unmet therapeutic needs in epilepsy? Are there ways to de-risk the transition from preclinical to clinical studies? Are there ways to improve the efficiency of clinical trials and to design ad hoc trials for the unmet therapeutic needs?

SUMMARY

Development and validation of a new, integrated strategy for antiepilepsy drug development is needed to identify truly innovative drugs.

The enigma of placebo effects in drug-refractory epilepsies

Placebo effects in the therapy of epilepsy were already known before the introduction of effective antiepileptic drugs (AEDs). They have physiologic correlates, and are even stronger in other neurologic disorders such as pain. Placebo effects in epilepsy have many facets. Our understanding of this phenomenon has increased in the last two decades: placebo effects are stronger in children than in adults, and may be culture- and setting-dependent; and impressive placebo effects occur in animals with epilepsy as well. More research is needed to fully elucidate the mechanism of placebo effects in epilepsy care, particularly as we go forth with studies addressing the issue of pharmacoresistance.

Epilepsy treatment: a paradigm shift is urgently need

Epilepsy affects between 5 and 10 people in a 1,000 and carries considerable morbidity and premature mortality. The complex inheritance pattern of a lowered seizure threshold is not fully understood but is likely to be polygenic. In the majority of people with epilepsy, we do not understand the pathophysiology, how a seizure is triggered, and how it can be prevented. In the centennial year of the discovery of the antiepileptic properties of phenobarbital, we have over 20 antiepileptic drugs; however, none have dramatically changed the long-term prognosis of the condition. The cascade of events triggering epilepsy is likely to vary greatly among individuals. The hope for the future is a shift of paradigm away from the symptomatic approach that currently exists. Indeed, once epileptogenesis is fully understood, treatment can be targeted at specific mechanisms, and then we will have truly disease-modifying therapies.