Dose-Response Study of Vigabatrin as add-on therapy in patients with uncontrolled complex partial seizures

Efficacy and safety of add-on antiseizure medications for focal epilepsy: A network meta-analysis

OBJECTIVE

Several antiseizure medications (ASMs) have been approved for the treatment of focal epilepsy. However, there is a paucity of evidence on direct comparison of ASMs. We evaluated the comparative efficacy and safety of all approved add-on ASMs for the treatment of focal epilepsy using network meta-analysis.

METHODS

Data through extensive literature search was retrieved from PubMed, Embase, Cochrane, and ClinicalTrial.gov databases using predefined search terms from inception through March 2023. PRISMA reporting guidelines (CRD42023403450) were followed in this study. Efficacy outcomes assessed were ≥50%, ≥75%, and 100% responder rates. Patient retention rate and safety outcomes such as overall treatment-emergent adverse events (TEAEs) and individual TEAEs were assessed. "Gemtc" 4.0.4 package was used to perform Bayesian analysis. Outcomes are reported as relative risks (RRs) and 95% confidence interval (CI).

RESULTS

Literature search retrieved 5807 studies of which, 75 studies were included in the analysis. All ASMs showed significantly higher ≥50% responder rate compared with placebo. Except the ≥75% seizure frequency reduction for zonisamide (2.23; 95% CI: 1.00-5.70) and 100% for rufinamide (2.03; 95% CI: 0.54-11.00), all other interventions showed significantly higher ≥75% and 100% responder rates compared with placebo. Among treatments, significantly higher 100% responder rate was observed with cenobamate compared to eslicarbazepine (10.71; 95% CI: 1.56-323.9) and zonisamide (10.63; 95% CI: 1.37-261.2). All ASMs showed a lower patient retention rate compared to placebo, with the least significant value observed for oxcarbazepine (0.77; 95% CI: 0.7-0.84). Levetiracetam showed a lower risk of incidence (1.0; 95%CI: 0.94-1.1; SUCRA: 0.885067) for overall TEAE compared with other medications.

SIGNIFICANCE

All approved ASMs were effective as add-on treatment for focal epilepsy. Of the ASMs included, cenobamate had the greatest likelihood of allowing patients to attain seizure freedom.

PLAIN LANGUAGE SUMMARY

This article compares the efficacy and safety of antiseizure medications (ASMs) currently available to neurologists in the treatment of epileptic patients. Several newer generation ASMs that have been developed may be as effective or better than the older medications. We included 75 studies in the analysis. In comparison, all drugs improved ≥50%, ≥75% and 100% responder rates compared to control, except for Zonisamide and Rufinamide in the ≥75% and 100% responder rate categories. Retention of patients undergoing treatment was lower in drugs than placebo. All drugs were tolerated, the levetiracetam showed the best tolerability. Cenobamate more likely help completely to reduce seizures.

Established and emerging GABAA receptor pharmacotherapy for epilepsy

Drugs that modulate the GABAA receptor are widely used in clinical practice for both the long-term management of epilepsy and emergency seizure control. In addition to older medications that have well-defined roles for the treatment of epilepsy, recent discoveries into the structure and function of the GABAA receptor have led to the development of newer compounds designed to maximise therapeutic benefit whilst minimising adverse effects, and whose position within the epilepsy pharmacologic armamentarium is still emerging. Drugs that modulate the GABAA receptor will remain a cornerstone of epilepsy management for the foreseeable future and, in this article, we provide an overview of the mechanisms and clinical efficacy of both established and emerging pharmacotherapies.

Psychobehavioural and Cognitive Adverse Events of Anti-Seizure Medications for the Treatment of Developmental and Epileptic Encephalopathies

The developmental and epileptic encephalopathies encompass a group of rare syndromes characterised by severe drug-resistant epilepsy with onset in childhood and significant neurodevelopmental comorbidities. The latter include intellectual disability, developmental delay, behavioural problems including attention-deficit hyperactivity disorder and autism spectrum disorder, psychiatric problems including anxiety and depression, speech impairment and sleep problems. Classical examples of developmental and epileptic encephalopathies include Dravet syndrome, Lennox-Gastaut syndrome and tuberous sclerosis complex. The mainstay of treatment is with multiple anti-seizure medications (ASMs); however, the ASMs themselves can be associated with psychobehavioural adverse events, and effects (negative or positive) on cognition and sleep. We have performed a targeted literature review of ASMs commonly used in the treatment of developmental and epileptic encephalopathies to discuss the latest evidence on their effects on behaviour, mood, cognition, sedation and sleep. The ASMs include valproate (VPA), clobazam, topiramate (TPM), cannabidiol (CBD), fenfluramine (FFA), levetiracetam (LEV), brivaracetam (BRV), zonisamide (ZNS), perampanel (PER), ethosuximide, stiripentol, lamotrigine (LTG), rufinamide, vigabatrin, lacosamide (LCM) and everolimus. Bromide, felbamate and other sodium channel ASMs are discussed briefly. Overall, the current evidence suggest that LEV, PER and to a lesser extent BRV are associated with psychobehavioural adverse events including aggressiveness and irritability; TPM and to a lesser extent ZNS are associated with language impairment and cognitive dulling/memory problems. Patients with a history of behavioural and psychiatric comorbidities may be more at risk of developing psychobehavioural adverse events. Topiramate and ZNS may be associated with negative effects in some aspects of cognition; CBD, FFA, LEV, BRV and LTG may have some positive effects, while the remaining ASMs do not appear to have a detrimental effect. All the ASMs are associated with sedation to a certain extent, which is pronounced during uptitration. Cannabidiol, PER and pregabalin may be associated with improvements in sleep, LTG is associated with insomnia, while VPA, TPM, LEV, ZNS and LCM do not appear to have detrimental effects. There was variability in the extent of evidence for each ASM: for many first-generation and some second-generation ASMs, there is scant documented evidence; however, their extensive use suggests favourable tolerability and safety (e.g. VPA); second-generation and some third-generation ASMs tend to have the most robust evidence documented over several years of use (TPM, LEV, PER, ZNS, BRV), while evidence is still being generated for newer ASMs such as CBD and FFA. Finally, we discuss how a variety of factors can affect mood, behaviour and cognition, and untangling the associations between the effects of the underlying syndrome and those of the ASMs can be challenging. In particular, there is enormous heterogeneity in cognitive, behavioural and developmental impairments that is complex and can change naturally over time; there is a lack of standardised instruments for evaluating these outcomes in developmental and epileptic encephalopathies, with a reliance on subjective evaluations by proxy (caregivers); and treatment regimes are complex involving multiple ASMs as well as other drugs.

Vigabatrin-related adverse events for the treatment of epileptic spasms: systematic review and meta-analysis

Objective: Although vigabatrin (VGB) is effective and well tolerated for the treatment of epileptic spasms, there are safety concerns. The aim of this systematic review and metaanalysis was to assess adverse events of VGB for the treatment of epileptic spasms. Methods: MEDLINE, EMBASE, and Cochrane databases were searched. The population was infants treated with VGB for epileptic spasms. The outcomes were VGB-related adverse events. Meta-analyses of VGB-related MRI abnormalities, retinal toxicity as measured by electroretinogram (ERG), visual field defect as measured by perimetry, and other adverse events were conducted. Results: Fifty-seven articles were included in the systematic review. The rate of VGB-related MRI abnormalities was 21% (95% CI: 15-29%). Risk factors for MRI abnormalities were age younger than 12 months and higher VGB dose. VGB-related retinal toxicity and visual field defect occurred in 29% (95% CI: 7-69%) and 28% (95% CI: 4-78%) respectively. Other adverse events occurred in 23% (95% CI: 16-34%), consisting predominantly of central nervous system symptoms, and the majority of these did not require therapeutic modification. Conclusion: This study will inform physicians and families on the risk profile of VGB for the treatment of epileptic spasms and will help decisions on treatment options.

Vigabatrin add-on therapy for drug-resistant focal epilepsy

BACKGROUND

This is an updated version of the original Cochrane Review published in 2008 and updated in 2013. Epilepsy is a common neurological condition which affects up to 1% of the population. Approximately 30% of people with epilepsy do not respond to treatment with currently available drugs. The majority of these people have focal epilepsy. Vigabatrin is an antiepileptic drug licensed for use in drug-resistant epilepsy.

OBJECTIVES

To assess the efficacy and tolerability of vigabatrin as an add-on therapy for people with drug-resistant focal epilepsy.

SEARCH METHODS

For the latest update of this review, we searched the following databases on 1 November 2018: Cochrane Register of Studies (CRS Web), MEDLINE (Ovid 1946 to 31 October 2018), ClinicalTrials.gov and the World Health Organization International Clinical Trials Registry Platform. The Cochrane Epilepsy Group Specialized Register and the Cochrane Central Register of Controlled Trials (CENTRAL) are both included in the Cochrane Register of Studies (CRS Web). We checked reference lists of retrieved studies for additional reports of relevant studies and contacted Hoechst Marion Roussel (manufacturers of vigabatrin) in 2000.

SELECTION CRITERIA

We included randomised, double-blind, placebo-controlled, fully published trials of vigabatrin in people of any age with drug-resistant focal epilepsy.

DATA COLLECTION AND ANALYSIS

Two review authors assessed trials for inclusion and extracted data using the standard methodological procedures expected by Cochrane. Primary analysis was by intention-to-treat (ITT). We evaluated: 50% or greater reduction in seizure frequency, treatment withdrawal, adverse effects, dose-response analysis, cognitive outcomes and quality of life. We presented results as risk ratios (RR) with 95% or 99% confidence intervals (CI).

MAIN RESULTS

We identified 11 trials that included 756 participants (age range: 10 to 64 years). The trials tested vigabatrin doses between 1 g/day and 6 g/day. All 11 trials displayed a risk of bias across at least three risk of bias domains. Predominantly, the risk of bias was associated with: allocation concealment (selection bias), blinding of outcome assessment (detection bias) and incomplete outcome data (attrition bias). Participants treated with vigabatrin may be two to three times more likely to obtain a 50% or greater reduction in seizure frequency compared with those treated with placebo (RR 2.60, 95% CI 1.87 to 3.63; 4 studies; low-certainty evidence). Those treated with vigabatrin may also be three times more likely to have treatment withdrawn although we are uncertain (RR 2.86, 95% CI 1.25 to 6.55; 4 studies; very low-certainty evidence). Compared to placebo, participants given vigabatrin were more likely to experience adverse effects: dizziness/light-headedness (RR 1.74, 95% CI 1.05 to 2.87; 9 studies; low-certainty evidence), fatigue (RR 1.65, 95% CI 1.08 to 2.51; 9 studies; low-certainty evidence), drowsiness (RR 1.70, 95% CI 1.18 to 2.44; 8 studies) and depression (RR 3.28, 95% CI 1.30 to 8.27; 6 studies). Although the incidence rates were higher among participants receiving vigabatrin compared to those receiving placebo, the effect was not significant for the following adverse effects: ataxia (RR 2.76, 95% CI 0.96 to 7.94; 7 studies; very low-certainty evidence), nausea (RR 3.57, 95% CI 0.63 to 20.30; 4 studies), abnormal vision (RR 1.64, 95% CI 0.67 to 4.02; 5 studies; very low-certainty evidence), headache (RR 1.23, 95% CI 0.79 to 1.92; 9 studies), diplopia (RR 1.76, 99% CI 0.94 to 3.30) and nystagmus (RR 1.53, 99% CI 0.62 to 3.76; 2 studies; low-certainty evidence). Vigabatrin had little to no effect on cognitive outcomes or quality of life.

AUTHORS' CONCLUSIONS

Vigabatrin may significantly reduce seizure frequency in people with drug-resistant focal epilepsy. The results largely apply to adults and should not be extrapolated to children under 10 years old. Short-term follow-up of participants showed that some adverse effects were associated with its use. Analysis of longer-term observational studies elsewhere, however, has demonstrated that vigabatrin use can lead to the development of visual field defects.

Rashes and other hypersensitivity reactions associated with antiepileptic drugs: A review of current literature

This article provides an overview of the pathogenesis and risk factors associated with antiepileptic drug (AED) hypersensitivity reactions, provides prescribing guidelines that may minimize the risk of antiepileptic induced rashes, and discusses treatment options for rashes. Articles indexed in PubMed, Science Citation, and Google Scholar (January 1946-March 2019) were systematic searched using the following key terms: hypersensitivity, rash, antiepileptic, epilepsy, cross-sensitivity, desensitization, patch testing and supplemented with our clinical experiences. Additional references were identified from a review of literature citations. AEDs are associated with cutaneous adverse reactions. Aromatic AEDs and higher titration rates are associated with increased risk of hypersensitivity reaction. Patient characteristics, underlying health conditions, and genetic variations may increase the likelihood of a hypersensitivity reaction. Once a hypersensitivity reaction occurs, the likelihood of cross sensitivity to another AED increases, especially among other aromatic AEDs. Withdrawal of the causal agent and initiation of a lower risk agent usually leads to resolution of symptoms. Desensitization protocols may be an option for patients whose seizures only respond to the AED causing the rash.

Efficacy of antiepileptic drugs in the adjunctive treatment of refractory partial-onset seizures: Meta-analysis of pivotal trials

OBJECTIVE

In the absence of randomized clinical trials (RCTs) assessing the relative efficacy of antiepileptic drugs (AEDs), meta-analyses are useful resources for informing treatment choices. This meta-analysis assesses the relative efficacy and tolerability of AEDs for adjunctive treatment of refractory partial onset seizures (POS).

METHODS

A systematic literature review was conducted to identify pivotal AED trials serving as the basis for US Food and Drug Administration (FDA) approval.

INCLUSION CRITERIA

1) double-blind, placebo-controlled, parallel-group design, with 8- to 14-week maintenance period; 2) enrolled patients ≥16years with refractory POS, including complex partial seizures; 3) study was conducted between 1993 and 2013; and; 4) patients received FDA-approved dosage. Outcomes analyzed: 1) 50% responder rate (≥50% reduction from baseline in seizure frequency); 2) seizure freedom (proportion of seizure-free patients); and 3) discontinuation due to adverse events (AEs). DerSimonian and Laird random-effects model was used to derive odds ratios (OR) and 95% confidence intervals (CI).

RESULTS

A total of 29 publications for 11 AEDs (eslicarbazepine, ezogabine, gabapentin, lacosamide, levetiracetam, perampanel, pregabalin, tiagabine, topiramate, vigabatrin, and zonisamide) were included in the meta-analysis. Tiagabine 56mg/day (OR 8.82, 95% CI: 2.77-28.11), pregabalin 600mg/day (OR 8.08, 95% CI: 5.45-11.98), and vigabatrin 3000mg/day (OR 6.23, 95% CI: 1.46-26.20) had the highest OR versus placebo of 50% response. The odds of seizure freedom were ≥7 times greater than placebo for levetiracetam 3000mg/day (OR 11.00, 95% CI: 2.08-58.06), vigabatrin 3000mg/day (OR 7.41, 95% CI: 1.31-41.84), and ezogabine 1200mg/day (OR 7.09, 95% CI: 0.36-58.06). Patients were more likely to discontinue any AED (except low-dose pregabalin) than placebo.

CONCLUSION

In this meta-analysis of >9000 patients, those treated with AEDs were more likely than placebo to achieve seizure response or freedom. Patients receiving pregabalin, tiagabine, and vigabatrin had the highest odds of ≥50% reduction in seizures, and patients receiving ezogabine, levetiracetam, and vigabatrin had the highest odds of seizure freedom.

Role of Endogenous Metabolite Alterations in Neuropsychiatric Disease

The potential role in neuropsychiatric disease risk arising from alterations and derangements of endogenous small-molecule metabolites remains understudied. Alterations of endogenous metabolite concentrations can arise in multiple ways. Marked derangements of single endogenous small-molecule metabolites are found in a large group of rare genetic human diseases termed "inborn errors of metabolism", many of which are associated with prominent neuropsychiatric symptomology. Whether such metabolites act neuroactively to directly lead to distinct neural dysfunction has been frequently hypothesized but rarely demonstrated unequivocally. Here we discuss this disease concept in the context of our recent findings demonstrating that neural dysfunction arising from accumulation of the schizophrenia-associated metabolite l-proline is due to its structural mimicry of the neurotransmitter GABA that leads to alterations in GABA-ergic short-term synaptic plasticity. For cases in which a similar direct action upon neurotransmitter binding sites is suspected, we lay out a systematic approach that can be extended to assessing the potential disruptive action of such candidate disease metabolites. To address the potentially important and broader role in neuropsychiatric disease, we also consider whether the more subtle yet more ubiquitous variations in endogenous metabolites arising from natural allelic variation may likewise contribute to disease risk but in a more complex and nuanced manner.

Practice guideline update summary: Efficacy and tolerability of the new antiepileptic drugs II: Treatment-resistant epilepsy: Report of the American Epilepsy Society and the Guideline Development, Dissemination, and Implementation Subcommittee of the American Academy of Neurology

Objective: To update the 2004 American Academy of Neurology (AAN) guideline for managing treatment-resistant (TR) epilepsy with second- and third-generation antiepileptic drugs (AEDs). Methods: 2004 criteria were used to systematically review literature (January 2003 to November 2015), classify pertinent studies according to the therapeutic rating scheme, and link recommendations to evidence strength. Results: Forty-two articles were included. Recommendations: The following are established as effective to reduce seizure frequency (Level A): immediate-release pregabalin and perampanel for TR adult focal epilepsy (TRAFE); vigabatrin for TRAFE (not first-line treatment; rufinamide for Lennox-Gastuat syndrome (LGS) (add-on therapy). The following should be considered to decrease seizure frequency (Level B): lacosamide, eslicarbazepine, and extended-release topiramate for TRAFE (ezogabine production discontinued); immediate- and extended-release lamotrigine for generalized epilepsy with TR generalized tonic-clonic (GTC) seizures in adults; levetiracetam (add-on therapy) for TR childhood focal epilepsy (TRCFE) (1 month to 16 years), TR GTC seizures, and TR juvenile myoclonic epilepsy; clobazam for LGS (add-on therapy); zonisamide for TRCFE (6-17 years); oxcarbazepine for TRCFE (1 month to 4 years). The text presents Level C recommendations. AED selection depends on seizure/syndrome type, patient age, concomitant medications, and AED tolerability, safety, and efficacy. This evidence-based assessment informs AED prescription guidelines for TR epilepsy and indicates seizure types and syndromes needing more evidence. A recent FDA strategy allows extrapolation of efficacy across populations; therefore, for focal epilepsy, eslicarbazepine and lacosamide (oral only for pediatric use) as add-on or monotherapy in persons ≥4 years of age and perampanel as monotherapy received FDA approval.

Practice guideline update summary: Efficacy and tolerability of the new antiepileptic drugs II: Treatment-resistant epilepsy

Objective

To update the 2004 American Academy of Neurology guideline for managing treatment-resistant (TR) epilepsy with second- and third-generation antiepileptic drugs (AEDs).

Methods

2004 criteria were used to systemically review literature (January 2003 to November 2015), classify pertinent studies according to the therapeutic rating scheme, and link recommendations to evidence strength.

Results

Forty-two articles were included.

Recommendations

The following are established as effective to reduce seizure frequency (Level A): immediate-release pregabalin and perampanel for TR adult focal epilepsy (TRAFE); vigabatrin for TRAFE (not first-line treatment); rufinamide for Lennox-Gastaut syndrome (LGS) (add-on therapy). The following should be considered to decrease seizure frequency (Level B): lacosamide, eslicarbazepine, and extended-release topiramate for TRAFE (ezogabine production discontinued); immediate- and extended-release lamotrigine for generalized epilepsy with TR generalized tonic-clonic (GTC) seizures in adults; levetiracetam (add-on therapy) for TR childhood focal epilepsy (TRCFE) (1 month–16 years), TR GTC seizures, and TR juvenile myoclonic epilepsy; clobazam for LGS (add-on therapy); zonisamide for TRCFE (6–17 years); oxcarbazepine for TRCFE (1 month–4 years). The text presents Level C recommendations. AED selection depends on seizure/syndrome type, patient age, concomitant medications, and AED tolerability, safety, and efficacy. This evidence-based assessment informs AED prescription guidelines for TR epilepsy and indicates seizure types and syndromes needing more evidence. A recent Food and Drug Administration (FDA) strategy allows extrapolation of efficacy across populations; therefore, for focal epilepsy, eslicarbazepine and lacosamide (oral only for pediatric use) as add-on or monotherapy in persons ≥4 years of age and perampanel as monotherapy received FDA approval.

Sabril® registry 5-year results: Characteristics of adult patients treated with vigabatrin

Vigabatrin (Sabril®), approved in the US in 2009, is currently indicated as adjunctive therapy for refractory complex partial seizures (rCPS) in patients ≥ 10 years old who have responded inadequately to several alternative treatments and as monotherapy for infantile spasms (IS) in patients 1 month to 2 years of age. Because of reports of vision loss following vigabatrin exposure, FDA approval required a risk evaluation mitigation strategy (REMS) program. Vigabatrin is only available in the US through Support, Help, And Resources for Epilepsy (SHARE), which includes a mandated registry. This article describes 5 years of demographic and treatment exposure data from adult patients (≥ 17 years old) in the US treated with vigabatrin and monitored in the ongoing Sabril® registry. Registry participation is mandatory for all US Sabril® prescribers and patients. A benefit-risk assessment must be documented by the physician for a patient to progress to maintenance therapy, defined as 1 month of vigabatrin treatment for patients with IS and 3 months for patients with rCPS. Ophthalmologic assessments must be documented during and after completion of therapy. As of August 26, 2014, a total of 6823 patients were enrolled in the registry, of which 1200 were adults at enrollment. Of these patients, 1031 (86%) were naïve to vigabatrin. The majority of adult patients (n=783, 65%) had previously been prescribed ≥ 4 AEDs, and 719 (60%) were receiving ≥ 3 concomitant AEDs at vigabatrin initiation. Prescribers submitted an initial ophthalmological assessment form for 863 patients; an ophthalmologic exam was not completed for 300 (35%) patients and thus, were considered exempted from vision testing. Of these patients, 128 (43%) were exempted for neurologic disabilities. Clinicians discontinued treatment in 8 patients because of visual field deficits (VFD) (5 patients naïve to vigabatrin and 3 patients previously exposed). Based on Kaplan-Meier survival estimates, it is estimated that approximately 71%, 55%, and 40% of adult patients naïve to vigabatrin would remain in the registry at 3, 6, and 12 months, respectively. These demographic data suggest that a proportion of adult patients remain on vigabatrin long-term despite the risks of adverse events and significant underlying AED resistance and neurologic disease.

Population pharmacokinetics analysis of vigabatrin in adults and children with epilepsy and children with infantile spasms

BACKGROUND AND OBJECTIVES

Vigabatrin is an inhibitor of γ-aminobutyric acid transaminase. The purpose of these analyses was to develop a population pharmacokinetics model to characterize the vigabatrin concentration-time profile for adults and children with refractory complex partial seizures (rCPS) and for children with infantile spasms (IS); to identify covariates that affect its disposition, and to enable predictions of systemic vigabatrin exposure for patients 1-12 months of age.

METHODS

Vigabatrin pharmacokinetic data from six randomized controlled clinical trials and one open-label study were analyzed using nonlinear mixed-effects modeling. Data collected from 349 adults with rCPS and 119 pediatric patients with rCPS or IS were used in the analyses.

RESULTS

A two-compartment model with first-order elimination and transit-compartment absorption consisting of five transit compartments adequately described the vigabatrin concentration-time data for these adult and pediatric patient populations. An exponential error model was used to estimate inter-individual variability for the transit-rate constant (k tr) (24.2 %), elimination rate constant (k) (14.7 %) and apparent central volume of distribution (V c/F) (18 %). For the study of children with IS, inter-occasion variability was estimated for k tr (58.1 %) and relative bioavailability (F) (26.9 %). Covariate analysis indicated that age, creatinine clearance (CLCR), and body weight were important predictors of vigabatrin pharmacokinetic parameters. Vigabatrin apparent clearance increased with increasing CLCR, consistent with renal excretion (primary pathway of vigabatrin elimination). Rate of vigabatrin absorption was dependent on age. The rate was slower in younger patients, which resulted in a smaller predicted maximum concentration and longer predicted time to maximum concentrations. Vigabatrin V c/F, apparent inter-compartmental clearance between the central and peripheral compartment, and apparent peripheral volume of distribution were increased with greater patient body weights. Sex did not contribute significantly to vigabatrin pharmacokinetic variability.

CONCLUSION

The model adequately described vigabatrin pharmacokinetic and enabled predictions of systemic exposures in pediatric patients 1-12 months of age.

Drug-induced cerebellar ataxia: a systematic review

BACKGROUND AND OBJECTIVES

Cerebellar ataxia can be induced by a large number of drugs. We here conducted a systemic review of the drugs that can lead to cerebellar ataxia as an adverse drug reaction (ADR).

METHODS

We performed a systematic literature search in Pubmed (1966 to January 2014) and EMBASE (1988 to January 2014) to identify all of the drugs that can have ataxia as an ADR and to assess the frequency of drug-induced ataxia for individual drugs. Furthermore, we collected reports of drug-induced ataxia over the past 20 years in the Netherlands by querying a national register of ADRs.

RESULTS

Drug-induced ataxia was reported in association with 93 individual drugs (57 from the literature, 36 from the Dutch registry). The most common groups were antiepileptic drugs, benzodiazepines, and antineoplastics. For some, the number needed to harm was below 10. Ataxia was commonly reversible, but persistent symptoms were described with lithium and certain antineoplastics.

CONCLUSIONS

It is important to be aware of the possibility that ataxia might be drug-induced, and for some drugs the relative frequency of this particular ADR is high. In most patients, symptoms occur within days or weeks after the introduction of a new drug or an increase in dose. In general, ataxia tends to disappear after discontinuation of the drug, but chronic ataxia has been described for some drugs.

Vigabatrin pediatric dosing information for refractory complex partial seizures: results from a population dose-response analysis

We predicted vigabatrin dosages for adjunctive therapy for pediatric patients with refractory complex partial seizures (rCPS) that would produce efficacy comparable to that observed for approved adult dosages. A dose-response model related seizure-count data to vigabatrin dosage to identify dosages for pediatric rCPS patients. Seizure-count data were obtained from three pediatric and two adult rCPS clinical trials. Dosages were predicted for oral solution and tablet formulations. Predicted oral solution dosages to achieve efficacy comparable to that of a 1 g/day adult dosage were 350 and 450 mg/day for patients with body weight ranges 10-15 and >15-20 kg, respectively. Predicted oral solution dosages for efficacy comparable to a 3 g/day adult dosage were 1,050 and 1,300 mg/day for weight ranges 10-15 and >15-20 kg, respectively. Predicted tablet dosage for efficacy comparable to a 1 g/day adult dosage was 500 mg/day for weight ranges 25-60 kg. Predicted tablet dosage for efficacy comparable to a 3 g/day adult dosage was 2,000 mg for weight ranges 25-60 kg. Vigabatrin dosages were identified for pediatric rCPS patients with body weights ≥10 kg.

Population dose-response analysis of daily seizure count following vigabatrin therapy in adult and pediatric patients with refractory complex partial seizures

Vigabatrin is an irreversible inhibitor of γ-aminobutyric acid transaminase (GABA-T) and is used as an adjunctive therapy for adult patients with refractory complex partial seizures (rCPS). The purpose of this investigation was to describe the relationship between vigabatrin dosage and daily seizure rate for adults and children with rCPS and identify relevant covariates that might impact seizure frequency. This population dose-response analysis used seizure-count data from three pediatric and two adult randomized controlled studies of rCPS patients. A negative binomial distribution model adequately described daily seizure data. Mean seizure rate decreased with time after first dose and was described using an asymptotic model. Vigabatrin drug effects were best characterized by a quadratic model using normalized dosage as the exposure metric. Normalized dosage was an estimated parameter that allowed for individualized changes in vigabatrin exposure based on body weight. Baseline seizure rate increased with decreasing age, but age had no impact on vigabatrin drug effects after dosage was normalized for body weight differences. Posterior predictive checks indicated the final model was capable of simulating data consistent with observed daily seizure counts. Total normalized vigabatrin dosages of 1, 3, and 6 g/day were predicted to reduce seizure rates 23.2%, 45.6%, and 48.5%, respectively.

A review on antiepileptic drugs-dependent fatigue: pathophysiological mechanisms and incidence

Fatigue represents a common side effect of several drugs, however, the underlying mechanisms have not been well identified. A depression of the central nervous system (CNS) and/or changes in peripheral processes have been associated with the development of fatigue. Antiepileptic drugs (AEDs), generally decreasing CNS excitability, are used in the treatment of seizures as well as other neurological and psychiatric diseases. Fatigue is certainly a common AEDs' side effect, although a high degree of variability exists depending on both patients' characteristics and the drug used. Here, we delineate the pathophysiological central and peripheral mechanisms by which AEDs may cause fatigue also reviewing the available clinical data in order to assess a possible AEDs rank and highlight each AEDs related risk. It appears that drugs acting on the GABAergic system have the highest incidence (with tiagabine exception) of fatigue followed by Gabapentin and Levetiracetam whereas drugs mainly inhibiting sodium channels (Carbamazepine, Eslicarbazepine, Lamotrigine, Phenytoin and Valproate) have the lowest. However, the dose used, AEDs related side effects and patients' characteristics might influence the degree of fatigue observed.

Vigabatrin for partial-onset seizure treatment in patients with tuberous sclerosis complex

Vigabatrin (VGB) has been shown to be particularly effective in the treatment of infantile spasms for those with tuberous sclerosis complex (TSC). However, many patients with TSC continue to have treatment-resistant seizures. For many patients with TSC, partial-onset seizures are prominent. Therefore, we examined the efficacy and tolerability of VGB for treatment of refractory partial-onset seizures. We performed a retrospective cohort study on 49 TSC patients with treatment-resistant seen at our center from 1997 to 2010, examined seizure outcomes, and reported adverse effects. We found that 13 (24.5%) patients became seizure-free or experienced a >90% decrease in seizure episode frequency with the addition of VGB to their regimens. Only one patient stopped VGB use because of excess sedation. The remaining 21 patients discontinued VGB use because of lack of efficacy. We conclude that VGB may be a safe and effective treatment in TSC patients with refractory partial-onset seizures.

Vigabatrin for refractory partial epilepsy

BACKGROUND

Epilepsy is a common neurological condition which affects between 0.5% and 1% of the population. Approximately 30% of people with epilepsy do not respond to treatment with currently available drugs. The majority of these people have partial epilepsy. Vigabatrin is an antiepileptic drug licensed for use in the treatment of refractory epilepsy. No major side effects associated with the use of vigabatrin were detected by initial randomised controlled trials of the drug. However, longer-term observational studies have subsequently identified that its use is associated with asymptomatic visual field constriction.

OBJECTIVES

The objective of this review was to synthesise evidence from short-term, randomised, placebo-controlled trials of vigabatrin. We summarised the effects of vigabatrin on seizures and short-term side effects when used as an add-on treatment for people with drug-resistant partial epilepsy. A review of longer-term observational studies and estimates of proportions of patients developing visual field constrictions is currently being undertaken and results will be cited in this review in due course.

SEARCH METHODS

We searched the Cochrane Epilepsy Group Specialised Register (12 October 2012), the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library 2012, Issue 9), MEDLINE (1946 to October week 1, 2012) and reference lists of articles. We also contacted the manufacturers of vigabatrin (Hoechst Marion Roussel).

SELECTION CRITERIA

We included randomised, double-blind, placebo-controlled, fully published trials of vigabatrin in people with drug-resistant partial epilepsy.

DATA COLLECTION AND ANALYSIS

Two review authors assessed trials for inclusion and extracted data. Primary analysis was by intention-to-treat (ITT). Outcomes evaluated included 50% or greater reduction in seizure frequency, treatment withdrawal and side effects observable in the short term. Results are presented on the risk ratio (RR) scale with 95% or 99% confidence intervals (CI).

MAIN RESULTS

Eleven suitable trials that tested vigabatrin doses between 1000 mg and 6000 mg were identified and included in the analysis. There were 982 observations on 747 patients in the primary ITT analysis of treatment efficacy. Patients treated with vigabatrin were significantly more likely to obtain a 50% or greater reduction in seizure frequency compared with those treated with placebo (RR 2.58, 95% CI 1.87 to 3.57). Those treated with vigabatrin were also significantly more likely to have treatment withdrawn (RR 2.49, 95% CI 1.05 to 5.88), and were more likely to experience a number of side effects, significantly so for fatigue or drowsiness. There was some evidence of small study effect bias, with smaller studies tending to report greater estimates of RR than larger studies. It is possible, therefore, that the actual RR of obtaining 50% reduction in seizure frequency is less than that obtained by a meta-analysis of fully published studies.

AUTHORS' CONCLUSIONS

This review of randomised controlled trials showed that vigabatrin can reduce seizure frequency in people with drug-resistant partial epilepsy. Short-term follow-up of patients showed that some side effects were associated with its use. Further analysis of longer-term observational studies is required to evaluate how likely patients are to develop visual field defects and whether such side effects are associated with dose and duration of drug use.

The cognitive impact of antiepileptic drugs

Effective treatment of epilepsy depends on medication compliance across a lifetime, and studies indicate that drug tolerability is a significant limiting factor in medication maintenance. Available antiepileptic drugs (AEDs) have the potential to exert detrimental effects on cognitive function and therefore compromise patient wellbeing. On the other hand, some agents may serve to enhance cognitive function. In this review paper, we highlight the range of effects on cognition linked to a variety of newer and older AEDs, encompassing key alterations in both specific executive abilities and broader neuropsychological functions. Importantly, the data reviewed suggest that the effects exerted by an AED could vary depending on both patient characteristics and drug-related variables. However, there are considerable difficulties in evaluating the available evidence. Many studies have failed to investigate the influence of patient and treatment variables on cognitive functioning. Other difficulties include variation across studies in relation to design, treatment group and assessment tools, poor reporting of methodology and poor specification of the cognitive abilities assessed. Focused and rigorous experimental designs including a range of cognitive measures assessing more precisely defined abilities are needed to fill the gaps in our knowledge and follow up reported patterns in the literature. Longitudinal studies are needed to improve our understanding of the influence of factors such as age, tolerance and the stability of cognitive effects. Future trials comparing the effects of commonly prescribed agents across patient subgroups will offer critical insight into the role of patient characteristics in determining the cognitive impact of particular AEDs.

Mechanism of action of vigabatrin: correcting misperceptions

Discovered more than three decades ago, vigabatrin is approved in more than 50 countries as adjunctive therapy for adult patients with refractory complex partial seizures who have responded inadequately to several alternative treatments and as monotherapy for pediatric patients aged 1 month to 2 years with infantile spasms. Contrary to a fairly common misperception, the compound's mechanism of action is very well-characterized in animal models and cell cultures. γ-Aminobutyric acid (GABA)-ergic synapses comprise approximately 30% of all synapses within the central nervous system, and therein underlies the primary mode of synaptic inhibition. Vigabatrin was rationally designed to have a specific effect on brain chemistry by inhibiting the GABA-degrading enzyme, GABA transaminase, resulting in a widespread increase in GABA concentrations in the brain. The increase in GABA functions as a brake on the excitatory processes that can initiate seizure activity. Despite the short half-life of vigabatrin in the body (5-7 h) and its relatively low concentration in cerebrospinal fluid (10% of the concentration observed in plasma), it has the profound effect of increasing GABA concentration in the brain for more than a week after a single dose in humans. This effect persists steadily over years of vigabatrin administration and results in significant and persistent decreases in seizure activity. Vigabatrin can be effective with once-daily dosing. Because of its specificity, vigabatrin has helped researchers explore the specific mechanisms within the brain that underlie seizure activity.

Non-vision adverse events with vigabatrin therapy

Vigabatrin is an effective antiepileptic drug (AED) for the treatment of refractory complex partial seizures (rCPS) and infantile spasms (IS). In clinical trials, vigabatrin was generally well-tolerated with an adverse event profile similar to that of other AEDs. The most common treatment-related adverse events were central nervous system effects, including drowsiness, dizziness, headache, and fatigue, with adjunctive vigabatrin in adults with rCPS, and sedation, somnolence, and irritability with vigabatrin monotherapy in infants with IS. Vigabatrin had little effect on cognitive function, mood, or behavior in a battery of neuropsychologic tests for rCPS. In placebo-controlled clinical trials, the incidence of depression and psychosis, but not other psychiatric adverse events, was greater with vigabatrin than placebo. Intramyelinic edema (IME) was initially identified in rats and dogs and led to a temporary suspension of clinical trials in the United States. IME was subsequently correlated with delays in evoked potential (EP) and increased T(2) -weighted signals on magnetic resonance imaging (MRI). Clinical trials of vigabatrin were allowed to resume after IME was not detected by neuropathologic assessments of autopsy and neurosurgical specimens or by serial EP or MRI assessments in older children and adults receiving vigabatrin. Subsequently, MRI abnormalities characterized by increased T(2) intensity and restricted diffusion were identified in infants treated with vigabatrin for IS. These abnormalities generally resolved with discontinuation of vigabatrin and, in some cases, during continued therapy. The benefit of improved seizure control must be balanced against the potential risks associated with vigabatrin, including abnormal MRI changes and other vigabatrin-related safety issues.

Balancing clinical benefits of vigabatrin with its associated risk of vision loss

Vigabatrin is an effective and well-tolerated antiepileptic drug (AED) for the treatment of refractory complex partial seizures (rCPS) and infantile spasms (IS), but its benefits must be evaluated in conjunction with its risk of retinopathy with the development of peripheral visual field defects (pVFDs). Vigabatrin should be considered for rCPS if a patient has failed appropriate trials of other AEDs or is not a suitable candidate for other AEDs, is not an optimal surgical candidate, and continues to experience debilitating effects from seizures. Vigabatrin is indicated as monotherapy for pediatric patients with IS. Its efficacy in achieving improved seizure control should be apparent within 12 weeks in patients with rCPS and within 2-4 weeks after attaining appropriate dosage for patients with IS. Because 12 weeks is well less than the known time of onset of visual defects, the risk of developing pVFDs may be minimized by discontinuing vigabatrin early during the course of therapy for patients with inadequate response. Appropriate vision screening is recommended at baseline, every 3 months during continued vigabatrin treatment, and at 3-6 months after discontinuation (if therapy has spanned more than a few months). If a pVFD is detected at any point and the decision is made to discontinue therapy, the pVFD is not likely to progress after discontinuation of vigabatrin. Although some patients will be at risk of retinopathy, vigabatrin is an appropriate treatment option for patients who achieve substantial clinical benefit, especially given the severe consequences of rCPS and uncontrolled IS. While retinopathy with the development of pVFDs is a serious adverse event, it is not life-threatening and its risk can be effectively managed.

Vigabatrin for childhood partial-onset epilepsies

To determine vigabatrin's effectiveness and the prevalence of symptomatic visual impairment (i.e., impairment affecting the ability to perform everyday activities) associated with its therapy in pediatric epilepsy, we retrospectively reviewed medical records of 156 patients receiving vigabatrin at Cincinnati Children's Medical Center from 1998-2010. In addition to demographics and vigabatrin dosing information, data included seizure type/frequency at presentation and subsequent follow-up. Of 156 patients, we excluded 35 because their medical records were insufficient to permit verification of the exact duration or timing of vigabatrin treatment. To evaluate efficacy (n = 121/135), we used a 5-point scale (0-4) to compare seizure frequency at several time points. To evaluate visual impairment (n = 63), we reviewed serial ophthalmologic evaluations at baseline and during treatment for patients in whom they were clinically indicated. Mean age at treatment initiation was 1.8 years (range, 0.1-29.2 years). Treatment duration ranged from 0.7-101.0 months, with an estimated average daily dose of 79 mg/kg/day. Tuberous sclerosis complex was the commonest seizure etiology (83%). Partial-onset seizure, alone or with infantile spasms, was the commonest seizure type (84%). Seizure frequency decreased from 3.7 ± 0.6 S.D. at baseline to 1.8 ± 1.7 S.D. at 6 months (P < 0.001). Responses to vigabatrin did not differ by tuberous sclerosis complex or nontuberous sclerosis complex etiology, and were sustained for 5 years. Sixty-three patients (∼50% of all patients evaluated) underwent clinically indicated ophthalmologic assessments during the review period. In our clinical judgment, no cases of clinically relevant vigabatrin-associated visual impairment occurred. Vigabatrin was effective for refractory childhood partial-onset epilepsy, and was not associated with symptomatic vision loss.

Registry initiated to characterize vision loss associated with vigabatrin therapy

The vigabatrin patient registry was implemented in August 2009 in conjunction with Food and Drug Administration approval of vigabatrin. All US vigabatrin-treated patients must enroll in the registry. Data on prescriber specialty/location, patient demographics, and clinical characteristics are collected. Benefit-risk assessments are required early in the course of therapy. Vision assessments are required at baseline (≤4 weeks after therapy initiation), every 3 months during therapy, and 3 to 6 months after discontinuation. As of February 1, 2011, 2473 patients (1500 with infantile spasms, 846 with refractory complex partial seizures, 120 with other diagnoses) had enrolled; 30.4% were previously exposed to vigabatrin. Kaplan-Meier analysis of time in registry indicated that 83 and 97% of all enrolled patients with refractory complex partial seizures and infantile spasms remained beyond 3 and 1 month, respectively. The ongoing registry will provide visual status and other information on vigabatrin-treated patients for both the infantile spasm and refractory complex partial seizure indications.

Vigabatrin therapy for refractory complex partial seizures: review of clinical trial experience in the United States

Vigabatrin is an antiepileptic drug used in more than 50 countries as adjunctive therapy for the treatment of refractory complex partial seizures (rCPS) in adults. First approved in the United Kingdom in 1989, vigabatrin was approved for use in the United States by the Food and Drug Administration in 2009. Although most clinical trials of vigabatrin have been conducted in Europe, three major trials, including two pivotal trials, were conducted in the United States. These trials have demonstrated efficacy and tolerability findings similar to those observed from the European trials. Results of the US trials have demonstrated vigabatrin to be an effective and generally well-tolerated therapy for rCPS in adults, with an optimal dosage of 3 g/day for most patients, and an onset of response generally within 2 weeks. This review focuses on the design and results of the three major US trials of vigabatrin in adults with rCPS.

Safety and efficacy of vigabatrin for the treatment of infantile spasms

In 2009, vigabatrin became the first FDA approved medication for the treatment of infantile spasms in the United States. There are few well-designed prospective studies comparing the drug to placebo or other modalities used in the treatment of infantile spasms. The available data have demonstrated that vigabatrin is efficacious in the treatment of infantile spasms regardless of underlying etiology, but that it is particularly beneficial in patients with a diagnosis of tuberous sclerosis. Adrenocorticotropic hormone (ACTH), the only other medication with robust efficacy data, has been used as first line therapy for infantile spasms associated with other etiologies, and in general controls spasms sooner than vigabatrin, though relapse is common with both therapies. Vigabatrin is generally well tolerated. However, use has been associated with permanent loss of peripheral vision in some patients. In children with tuberous sclerosis, vigabatrin should be considered as initial therapy for infantile spasms. It is a viable alternative for patients with suboptimal response, contraindications or intolerance to ACTH.

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.

New drugs for pediatric epilepsy

The last 2 decades have witnessed an unprecedented period of new antiepileptic drug (AED) development. Newer-generation AEDs have been developed with the intention of improving the ease of use, decreasing drug interactions, decreasing adverse side effects, and identifying drugs with unique mechanisms of action, some of which may bear relevance to potential neuroprotective activity. Drug trials have also been refined in some cases to evaluate AED efficacy in children and against distinct epilepsy syndromes. This progress provides many new treatment options for the child neurologist facing children with epilepsy but also introduces the burden of determining appropriate AED choices. Here we highlight 6 new antiepileptic medications recently approved or pending approval for use in the United States: lacosamide, rufinamide, vigabatrin, retigabine, brivaracetam, and clobazam. For each of these medications, we present information regarding the history of drug development, proposed mechanism(s) of action, pharmacokinetics and recommended dosing, evidence for clinical efficacy, tolerability, and when, available, any unique features that are relevant for the pediatric population.

Evaluating risks for vigabatrin treatment

Approximately 30 to 40 percent of adults with epilepsy treated chronically with vigabatrin develop concentric visual field constrictions. These deficits are generally mild and asymptomatic, but are usually irreversible, so risks and benefits for vigabatrin treatment must be carefully reviewed. Infantile spasms, a particularly severe form of epilepsy, may respond to vigabatrin; however, some infants treated with the drug develop MRI evidence of possible intramyelinic edema in subcortical structures. This article reviews the benefits of vigabatrin treatment, the risks it poses to the retina and the developing brain, as well as possible subgroups of adults and infants with severe epilepsy for whom treatment may, nevertheless, be warranted.

Placebo responses in randomized trials of antiepileptic drugs

This meta-analysis of published, randomized, controlled trials (RCTs) of antiepileptic drugs in adults with focal drug-resistant epilepsy was performed to estimate a mean placebo effect, to evaluate variability in placebo response rates, to investigate associations between placebo effect rates and study characteristics, and to determine whether there were changes in placebo response rates over recent years in RCTs (so-called "placebo drift"). One hundred ninety-eight potentially appropriate studies were identified after MEDLINE search and carefully reviewed. Twenty-seven RCTs (with 5662 randomized patients, including 1887 patients in placebo arms) were included in the meta-analysis. A random effects meta-analytic model estimated the pooled placebo response at 12.5% (95% CI: 10.03-14.94%). A statistically significant correlation between baseline median seizure frequency and placebo response rates was not observed. "Placebo drift" was not considered statistically significant.

Placebo-corrected efficacy of modern antiepileptic drugs for refractory epilepsy: systematic review and meta-analysis

Although adjunctive treatment with modern antiepileptic drugs (AEDs) is standard care in refractory epilepsy, it is unclear how much of the effect can be attributed directly to the AEDs and how much to the beneficial changes seen with placebo. Therefore, we performed a systematic review and meta-analysis of the evidence to determine the placebo-corrected net efficacy of adjunctive treatment with modern AEDs on the market for refractory epilepsy. Of 317 potentially eligible articles reviewed in full text, 124 (39%) fulfilled eligibility criteria. After excluding 69 publications, 55 publications of 54 studies in 11,106 adults and children with refractory epilepsy form the basis of evidence. The overall weighted pooled-risk difference in favor of AEDs over placebo for seizure-freedom in the total sample of adults and children was 6% [95% confidence interval (CI) 4-8, z = 6.47, p < 0.001] and 21% (95% CI 19-24, z = 17.13, p < 0.001) for 50% seizure reduction. Although the presence of moderate heterogeneity may reduce the validity of the results and limit generalizations from the findings, we conclude that the placebo-corrected efficacy of adjunctive treatment with modern AEDs is disappointingly small and suggest that better strategies of finding drugs are needed for refractory epilepsy, which is a major public health problem.

Treatment of refractory complex partial seizures: role of vigabatrin

Vigabatrin (VGB) is an antiepileptic drug that was designed to inhibit GABA-transaminase, and increase levels of gamma-amino-butyric acid (GABA), a major inhibitory neurotransmitter in the brain. VGB has demonstrated efficacy as an adjunctive antiepileptic drug for refractory complex partial seizures (CPS) and for infantile spasms (IS). This review focuses on its use for complex partial seizures. Although VGB is well tolerated, there have been significant safety concerns about intramyelinic edema and visual field defects. VGB is associated with a risk of developing bilateral concentric visual field defects. Therefore, the use of VGB for complex partial seizures should be limited to those patients with seizures refractory to other treatments. Patients must have baseline and follow-up monitoring of visual fields, early assessment of its efficacy, and ongoing evaluation of the benefits and risks of VGB therapy.

Vigabatrin for refractory partial epilepsy

BACKGROUND

Epilepsy is a common neurological condition which affects between 0.5% and 1% of the population. Approximately 30% of people with epilepsy do not respond to treatment with currently available drugs, and the majority of these people have partial epilepsy. Vigabatrin is an antiepileptic drug licensed for use in the treatment of refractory epilepsy. No major side effects associated with the use of vigabatrin were detected by initial randomised controlled trials of the drug. However, longer term observational studies have subsequently identified that its use is associated with asymptomatic visual field constriction.

OBJECTIVES

The objective of this review is to synthesise evidence from short-term, randomised, placebo-controlled trials of vigabatrin. We summarise the effects of vigabatrin on seizures and short-term side effects when used as an add-on treatment for people with drug-resistant partial epilepsy. A review of longer term observational studies and estimates of proportions of patients developing visual field constrictions is currently being undertaken and results will be cited here in due course.

SEARCH STRATEGY

We searched the Cochrane Epilepsy Group Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 1, 2008), MEDLINE (1950-March 2008), and reference lists of articles. We also contacted the manufacturers of vigabatrin (Hoechst Marion Roussel).

SELECTION CRITERIA

We included randomised, double-blind, placebo-controlled, fully published trials of vigabatrin, in people with drug-resistant partial epilepsy.

DATA COLLECTION AND ANALYSIS

Two review authors assessed trials for inclusion and extracted data. Primary analysis was by intention-to-treat (ITT). Outcomes evaluated included 50% or greater reduction in seizure frequency, treatment withdrawal and side effects observable in the short term. Results are presented on the relative risk (RR) scale with 95 or 99% confidence intervals (CI).

MAIN RESULTS

Eleven suitable trials, testing doses between 1000 mg and 6000 mg, were identified and included in the analysis. There were 982 observations on 747 patients in the primary ITT analysis of treatment efficacy. Patients treated with vigabatrin were significantly more likely to obtain a 50% or greater reduction in seizure frequency compared with those treated with placebo (RR 2.58 (95% CI 1.87 to 3.57)). Those treated with vigabatrin were also significantly more likely to have treatment withdrawn (RR 2.49 (95% CI 1.05 to 5.88)), and more likely to experience a number of side effects, significantly so for fatigue or drowsiness. There was some evidence of small study effect bias, with smaller studies tending to report greater estimates of RR than larger studies. It is possible that the actual relative risk of obtaining 50% reduction in seizure frequency may therefore be less than that obtained by a meta-analysis of fully published studies.

AUTHORS' CONCLUSIONS

This review of randomised controlled trials shows that vigabatrin can reduce seizure frequency in people with drug-resistant partial epilepsy. Short-term follow up of patients shows some side effects are associated with its use. Further analysis of longer term observational studies is required to evaluate how likely patients are to develop visual field defects, and whether such side effects are associated with dose and duration of drug use.

Advancements in the Treatment of Epilepsy

Diagnostic tools and treatment options for epilepsy have expanded in recent years. Imaging techniques once confined to research laboratories are now routinely used for clinical purposes. Medications that were unavailable a few years ago are now first-line agents. Patients with refractory seizures push for earlier surgical intervention, consider treatment with medical devices, and actively seek nonpharmacologic alternatives. We review some of these recent advances in the management of epilepsy.

The pharmacokinetics of vigabatrin in rat blood and cerebrospinal fluid

PURPOSE

Data on the blood pharmacokinetics of vigabatrin, an antiepileptic drug with a unique and novel mechanism of action, in the rat are sparse. Additionally, little is known of the kinetics of vigabatrin in the central cerebrospinal fluid (CSF) compartment. We therefore investigated the rate of penetration into and the inter-relationship between serum and CSF compartments following systemic administration of vigabatrin in the rat.

METHODS

Sprague-Dawley rats were implanted with a jugular vein catheter and a cisterna magna catheter for blood and CSF sampling, respectively. Vigabatrin was administered by intraperitonial injection at three different doses (250, 500 and 1000mg/kg) and blood and CSF collected at timed intervals up to 8h. Vigabatrin concentrations in sera and CSF were determined by high performance liquid chromatography.

RESULTS

Vigabatrin concentrations in blood and CSF rose linearly and dose-dependently and the time to maximum concentration (Tmax) was 0.4 and 1.0h, respectively. Vigabatrin is not protein bound in serum and its elimination from serum (mean t1/2 values, 1.1-1.4 h) is rapid and dose-independent. The efflux of vigabatrin from CSF was significantly slower than that seen for serum (mean t1/2 values, 2.2-3.3h).

CONCLUSIONS

The kinetics of vigabatrin are linear with rapid entry into CSF. However, although vigabatrin CSF kinetics parallel that seen in serum, CSF vigabatrin concentrations represent only 2% of concentrations seen in serum and do not reflect free drug concentrations in serum.

Pharmacotherapy of paediatric epilepsy

Childhood epilepsy is a common condition, with an annual incidence of approximately 40 of 100,000 in the first decade of life. Although childhood epilepsy is more likely to remit than epilepsy in adults, the developmental and social impact of epilepsy during childhood may extend beyond the childhood years, affecting the individual's potential in cognitive, emotional and socio-economic arenas. The goal of medical management of childhood epilepsy is seizure freedom, with minimal or no adverse effects. Achievement of this goal is crucial in the effort to minimise the long-term disabilities associated with childhood epilepsy. Pharmacotherapy is a cornerstone of management of childhood epilepsy. This review addresses some of the challenges in treatment of epilepsy, which are unique to childhood, and reviews the newer anticonvulsants available and what is known about their role in childhood epilepsy.

New antiepileptic drug therapies

The introduction of these new antiepileptic drugs, from felbamate to levetiracetam, raised hope of control of epilepsy with fewer adverse effects and improved quality of life. Unfortunately, many patients continue to experience refractory epilepsy despite the use of these new agents, and dose-related adverse effects and idiosyncratic reactions continue to be problematic. A recent report describes six new compounds in preclinical development, and five in clinical trials [131]. As the number of available, effective, but imperfect antiepileptic drugs increases, many challenges remain. These include: choosing the drug appropriate for the epileptic syndrome, assessing accurately the range of a drug's adverse effects in an individual patient, and considering carefully the drug's interactions in combination drug therapy. In considering drug combinations, differing mechanisms of drug action and favorable pharmacodynamic interactions (an area requiring additional studies) are of importance. Clinicians caring for children who have epilepsy anticipate further advances in the pharmacogenetics and molecular pathophysiology of epilepsy, leading to individually tailored, effective, and safe therapy.

Progress report on new antiepileptic drugs: a summary of the Fifth Eilat Conference (EILAT V)

The Fifth Eilat Conference on New Antiepileptic Drugs (AEDs) took place at the Dan Hotel, Eilat, Israel, 25-29 June 2000. Basic scientists, clinical pharmacologists and neurologists from 20 countries attended the conference, whose main themes included recognition of unexpected adverse effects, new indications of AEDs, and patient-tailored AED therapy. According to tradition, the central part of the conference was devoted to a review of AEDs in development, as well to updates on AEDs that have been marketed in recent years. This article summarizes the information presented on drugs in preclinical and clinical development, including AWD 131-138, DP-valproate, harkoseride, LY300164, NPS 1776, NW 1015, pregabalin, remacemide, retigabine, rufinamide and valrocemide. The potential value of an innovative strategy, porcine embryonic GABAergic cell transplants, is also discussed. Finally, updates on felbamate, fosphenytoin, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine, topiramate, vigabatrin, zonisamide, and the antiepileptic vagal stimulator device are presented.

Expanding the guidelines for electronic communication with patients: application to a specific tool

In 1998, the American Medical Informatics Association (AMIA) published a white paper entitled "Guidelines for the Clinical Use of Electronic Mail with Patients," which outlined a practical framework for this interaction. Interest in the use of other Internet-based tools, such as the World Wide Web, to enhance clinical communication is increasing. In such systems, static information can be made centrally available to patients and interactive tools such as messaging systems, schedules, and individualized care regimens can be integrated within the site. Site-specific guidelines are needed to address potential problems inherent in the particular services being offered. This article presents advice on developing site-specific guidelines, with examples, based on experience gained in developing and refining guidelines for the use of PatientWeb at the Massachusetts General Hospital Department of Neurology.

New anti-epileptic drugs for the 21st century

Prior to 1993, there were only six major drugs available in the US for the treatment of patients with epilepsy. These included phenobarbital (PB), phenytoin (PHT), carbamazepine (CBZ), primidone (PRIM), valproic acid/sodium valproate (VPA) and ethosuximide (ESX). Of these drugs, VPA has the broadest spectrum of activity and ESX the most limited. Despite these six agents, as well as several secondary drugs, it is estimated that over 30% of patients have inadequate seizure control, while others, whose disease is adequately controlled, suffer from bothersome adverse events (AEs). Since 1993, ten new drugs have entered the worldwide market (not all in the US). Those released include felbamate (FBM), gabapentin (GBP), lamotrigine (LTG), topiramate (TPM), tiagabine (TGB), oxcarbazepine (OXC), levetiracetam (LVT), zonisamide (ZNS), clobazam (CLB) and vigabatrin (VGB). The purpose of this article is to review each of the above drugs, looking at efficacy, safety, tolerability and where they may play a role in the current treatment of epilepsy.

Cortical function in epilepsy

Recent work with functional neuroimaging that relies on blood flow techniques, (15)O water positron emission tomography and functional magnetic resonance imaging has identified the lateralization and location of language functions. These technologies are increasingly being explored as alternatives to the more invasive intracarotid amytal procedure. Paradigms and sequences have been designed to identify the capacity of the hippocampus and mesial structures to support memory. Magnetoelectroencephalography offers the prospect of mapping language function in real time. Event-related data acquisition has also been employed to localize blood flow changes that are associated with interictal activity.

Vigabatrin: a novel therapy for seizure disorders

OBJECTIVE

To review the pharmacology, pharmacokinetics, efficacy, and adverse effects of vigabatrin and its role in the management of seizure disorders.

METHODS

A MEDLINE search of English-language literature from January 1993 through January 1999 was conducted using vigabatrin as a search term to identify pertinent studies and review articles. Additional studies were identified from the bibliographies of reviewed literature. The manufacturer provided postmarketing surveillance data. Priority was given to randomized, double-blind, placebo-controlled studies.

FINDINGS

Vigabatrin is a selective and irreversible inhibitor of gamma-aminobutyric acid transaminase. In controlled clinical trials of vigabatrin add-on therapy in patients with uncontrolled partial seizures, 24-67% of patients achieved a < or =50% reduction in seizure frequency. Data from two comparative trials with carbamazepine monotherapy indicate that vigabatrin monotherapy reduces the frequency of partial seizures in patients with newly diagnosed epilepsy. Vigabatrin also controls infantile spasms, particularly those associated with tuberous sclerosis. Vigabatrin is more effective in patients with partial seizures than in those with generalized seizures. The drug is generally well tolerated. Headache and drowsiness were the most common adverse effects observed in controlled clinical trials; visual field defects, psychiatric reactions, and hyperactivity also have been reported. There are no known clinically significant drug interactions.

CONCLUSIONS

Vigabatrin improves seizure control as add-on therapy for refractory partial seizures and may produce therapeutic benefits in the treatment of infantile spasms. Vigabatrin is generally well tolerated, with a convenient administration schedule, a lack of known significant drug interactions, and no need for routine monitoring of plasma concentrations.