Double-blind, placebo-controlled study of vigabatrin (gamma-vinyl GABA) in drug-resistant epilepsy

N-of-1 trials in epilepsy: A systematic review and lessons paving the way forward

OBJECTIVE

Defined as prospective single-patient crossover studies with repeated paired cycles of active and control intervention, N-of-1 trials have gained attention as an option to obtain high-quality evidence of efficacy, particularly for patients with rare epilepsies in whom conduction of well-powered randomized controlled trials can be challenging. The objective of this systematic review is to provide an appraisal of the literature on N-of-1 trials in individuals with epilepsy.

METHODS

We searched PubMed and Embase on January 12, 2024, for studies meeting the following criteria: prospectively planned, within-patient, multiple-crossover design in individuals with epilepsy and outcomes related to comorbidities. Information on design, outcome measurements, intervention, and analyses was retrieved. Risk of bias assessment was performed using the Risk of Bias in N-of-1 Trials (RoBiNT) scale. We highlighted methodological aspects of the N-of-1 trials identified and discuss future recommendations.

RESULTS

Five studies met our inclusion criteria. An additional multiple-crossover trial that evaluated treatment effects exclusively at group level was also included because of its relevance to N-of-1 study methodology. The studies enrolled individuals with focal seizures, absences or cognitive impairement and electrographic discharges. Treatments included established or investigational antiseizure medications, off-label medications, neurostimulation or lifestyle intervention. Three of the five N-of-1 trials reported on individual cases. The studies' strengths were the use of individualized treatment dosages and symptom-specific patient-reported outcomes. Limitations were related to minimal reporting of baseline characteristics and seizure burden.

SIGNIFICANCE

The trials identified by our search exemplify how the N-of-1 design can be applied to assess interventions in individuals with epilepsy-related disorders. Future N-of-1 trials of antiseizure interventions should take into account baseline seizure frequency, should apply statistical models suited to capture seizure frequency changes reliably and make predefined interim assessments. Non-seizure outcome measures evaluable over short periods should be considered. Tailored N-of-1 methodology could pave the way to evidence-based, treatment selection for patients with rare epilepsies.

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.

Pharmacokinetic evaluation of vigabatrin dose for the treatment of refractory focal seizures in children using adult and pediatric data

Vigabatrin is indicated as adjunctive therapy for refractory focal seizures. For children, European recommendations indicate maintenance doses varying from 30 to 100 mg/kg/day for this indication. Since cumulated dose was associated with retinal toxicity, it is essential to administrate the lowest effective dose to patients. This work was conducted with the purpose to determine the pediatric doses of vigabatrin that allow a similar exposure than effective doses in adults (2-3 g/day) through a pharmacokinetic (PK) study, using both pediatric and adult data. For this study, we focused on the active S(+) enantiomer of vigabatrin. First, the adult effective exposition range of vigabatrin-S was determined from an adult PK model. Then, this same model was scaled to the pediatric population using allometry and maturation principles to account for growth and development. The ability of the model to predict pediatric data was assessed by comparing population predictions with observed pediatric data. Finally, the extrapolated pediatric model was used to simulate pediatric expositions which were compared to the adult exposition range (36.5-77.9 mg.h/L). From those simulations, we determined that, for children aged between 3 months and 18 years, doses between 40 and 50 mg/kg/day allow vigabatrin-S expositions similar to those found in adults at the recommended posology. We proposed those doses as optimal maintenance doses that may be increased, if necessary, by slow titration.

Conflicting Effects of Methylglyoxal and Potential Significance of miRNAs for Seizure Treatment

According to an update from the World Health Organization, approximately 50 million people worldwide suffer from epilepsy, and nearly one-third of these individuals are resistant to the currently available antiepileptic drugs, which has resulted in an insistent pursuit of novel strategies for seizure treatment. Recently, methylglyoxal (MG) was demonstrated to serve as a partial agonist of the gamma-aminobutyric acid type A (GABA_A) receptor and to play an inhibitory role in epileptic activities. However, MG is also a substrate in the generation of advanced glycation end products (AGEs) that function by activating the receptor of AGEs (RAGE). The AGE/RAGE axis is responsible for the transduction of inflammatory cascades and appears to be an adverse pathway in epilepsy. This study systematically reviewed the significance of GABAergic MG, glyoxalase I (GLO1; responsible for enzymatic catalysis of MG cleavage) and downstream RAGE signaling in epilepsy. This work also discussed the potential of miRNAs that target multiple mRNAs and introduced a preliminary scheme for screening and validating miRNA candidates with the goal of reconciling the conflicting effects of MG for the future development of seizure treatments.

Epilepsy, Antiepileptic Drugs, and Aggression: An Evidence-Based Review

Antiepileptic drugs (AEDs) have many benefits but also many side effects, including aggression, agitation, and irritability, in some patients with epilepsy. This article offers a comprehensive summary of current understanding of aggressive behaviors in patients with epilepsy, including an evidence-based review of aggression during AED treatment. Aggression is seen in a minority of people with epilepsy. It is rarely seizure related but is interictal, sometimes occurring as part of complex psychiatric and behavioral comorbidities, and it is sometimes associated with AED treatment. We review the common neurotransmitter systems and brain regions implicated in both epilepsy and aggression, including the GABA, glutamate, serotonin, dopamine, and noradrenaline systems and the hippocampus, amygdala, prefrontal cortex, anterior cingulate cortex, and temporal lobes. Few controlled clinical studies have used behavioral measures to specifically examine aggression with AEDs, and most evidence comes from adverse event reporting from clinical and observational studies. A systematic approach was used to identify relevant publications, and we present a comprehensive, evidence-based summary of available data surrounding aggression-related behaviors with each of the currently available AEDs in both adults and in children/adolescents with epilepsy. A psychiatric history and history of a propensity toward aggression/anger should routinely be sought from patients, family members, and carers; its presence does not preclude the use of any specific AEDs, but those most likely to be implicated in these behaviors should be used with caution in such cases.

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.

Antiepileptic Drug Treatment in Children with Epilepsy

Most children with new-onset epilepsy achieve seizure freedom with appropriate antiepileptic drugs (AEDs). However, nearly 20 % will continue to have seizures despite AEDs, as either monotherapy or in combination. Despite the growing market of new molecules over the last 20 years, the proportion of drug-resistant epilepsies has not changed. In this review, we report the evidence of efficacy and safety based on phase III randomized controlled clinical trials (RCTs) of AEDs currently used in the paediatric population. We conducted a literature search using the PubMed database and the Cochrane Database of Systematic Reviews. We also analysed the RCTs of newer AEDs whose efficacy in adolescents and adults might suggest possible use in children. Most of the phase III trials on AEDs in children have major methodological limitations that considerably limit meaningful conclusions about comparative efficacy between old and new molecules. Since the efficacy of new drugs has only been reported versus placebo, the commonly held opinion that new and newer AEDs have a better safety profile than old ones does not appear to be supported by evidence. Despite limited solid evidence, pharmacological management has improved over the years as a consequence of increased awareness of some degree of specificity of treatment in relation to different epilepsy syndromes and attention to adverse events. Future research should be directed taking these factors, as well as the diversity of epilepsy, into consideration.

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.

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.

Vigabatrin therapy for refractory complex partial seizures: review of major European trials

Complex partial seizures (CPS) are a form of localization-related seizures associated with serious comorbidities and risks. CPS can be difficult to treat and may remain refractory to treatment with antiepileptic drugs (AEDs). Refractory CPS (rCPS) can be hazardous because of the potential for severe dysfunction and bodily harm, sometimes with fatal consequences. Control of seizure activity is critical to the clinical management of CPS. Vigabatrin is a unique AED approved in both Europe and the United States as adjunctive therapy for adult patients with rCPS who have responded inadequately to several alternative treatments. This review focuses on appropriately controlled studies of vigabatrin conducted in Europe. Several double-blind studies randomized those with rCPS to treatment with vigabatrin vs placebo, and two evaluated durability of response to long-term, open-label vigabatrin. Endpoints included seizure frequency, treatment satisfaction, and adverse events (AEs). Efficacy outcomes demonstrated that vigabatrin add-on therapy significantly reduced the frequency of seizures. Long-term studies indicated durability of response and tolerability of vigabatrin therapy for up to several years. Treatment satisfaction data indicated a preference for vigabatrin vs placebo for both physicians and study participants. Vigabatrin was well-tolerated with generally mild AEs considered common to AEDs. Vision effects were not formally monitored in these studies. In European trials, vigabatrin was efficacious as adjunctive therapy for rCPS.

Drug treatment of epilepsy in the century of the ILAE: the second 50 years, 1959-2009

The drug therapy of epilepsy evolved enormously in this 50 year period. Advances in therapeutics included the incorporation of pharmacokinetics into clinical practice, enormous advances in neurochemistry, a trend to antiepileptic drug monotherapy, better drug assessment, better understanding of therapeutic outcomes, and the recognition of the large epilepsy treatment gap in many countries. An unprecedented range of new drugs was introduced in this period. Before 1989, these included carbamazepine, valproate, ethosuximide, and the benzodiazepines. Since 1989, 13 more new drugs have been licensed and marketed and there are others in the pipeline. The International League Against Epilepsy and its leading figures have played an important role in these developments. In this period, too, there has been a rapid expansion in research and development within the pharmaceutical industry and a rise in the value of the antiepileptic drug market. In parallel, governmental regulation of pharmaceuticals has greatly increased. To what extent the overall prognosis of epilepsy has improved as a result of these activities is an interesting and perplexing question.

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.

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.

Seizure reduction and quality of life improvements in people with epilepsy

PURPOSE

Previous research suggests that seizure freedom may be necessary to improve health-related quality of life (HRQOL) for epilepsy surgery patients, but little is known regarding the seizure-frequency reduction needed to improve HRQOL among medically treated individuals.

METHODS

With data from 134 adults with refractory complex partial seizures participating in a randomized controlled antiepileptic drug (AED) trial, we compared the change in HRQOL across groups having different levels of change in seizure frequency: 100%, 75-99%, 50-74% reduction, and 0-50% increase or decrease. Changes over time within each seizure-reduction group also were assessed. HRQOL was measured by the QOLIE-31, QOLIE-89, and SF-36.

RESULTS

Subjects who became seizure free reported significantly more positive change than those who did not on the QOLIE-31 and QOLIE-89 overall scores, the QOLIE-89 mental health, physical health, and epilepsy-targeted composites, as well as the SF-36 mental health summary score. Changes over time in overall QOLIE-31 and QOLIE-89 scores were significantly more positive for subjects who achieved seizure freedom (i.e., 100% reduction in seizure frequency) than for those who did not. No significant change in QOLIE-31 and QOLIE-89 overall scores was observed for subjects who did not achieve seizure freedom.

CONCLUSIONS

In this study, HRQOL improvement occurred primarily among patients who achieved complete seizure freedom. Many AED trials use a 50% seizure-frequency reduction criterion as a trial end point, but measurable impacts of this degree of reduction in seizure frequency on HRQOL in this sample were not observed. These results further support striving for seizure freedom as an epilepsy care goal.

Human brain GABA transaminase tissue distribution and molecular expression

Human brain gamma-aminobutyrate transaminase is differentially expressed in a tissue-specific manner. mRNA master dot-blot analysis for 50 different human tissues, including different brain regions and fetal tissues, provided a complete map of the tissue distribution. Genomic Southern analysis revealed that the gamma-aminobutyrate transaminase gene is a single copy, at least 15 kb in size. In addition, human brain gamma-aminobutyrate transaminase cDNA was expressed in Escherichia coli using a pGEX expression vector system. Catalytically active gamma-aminobutyrate transaminase was expressed in large quantities and the purified recombinant enzyme had kinetic parameters that were indistinguishable from those isolated from other mammalian brains. The human enzyme was inactivated by a well-known antiepileptic drug vigabatrin. Values of Ki and kinact were 1 mM and 0.35 min-1, respectively. Results from inactivation kinetics suggested that human gamma-aminobutyrate transaminase is more sensitive to the vigabatrin drug than the enzyme isolated from bovine brain.

Adverse reactions to new anticonvulsant drugs

A lack of systematic pharmacoepidemiological studies investigating adverse drug reactions (ADRs) to anticonvulsants makes it difficult to assess accurately the incidence of anticonvulsant-related ADRs. Most of the available information in this regard stems from clinical trial experience, case reports and postmarketing surveillance, sources that are not, by any means, structured to provide precise data on adverse event epidemiology. For various ethical, statistical and logistical reasons, the organisation of structured clinical trials that are likely to provide substantial data on ADRs is extremely difficult. This review concentrates on current literature concerning serious and life-threatening ADRs. As with the older anticonvulsants, the majority of ADRs to newer anticonvulsants are CNS-related, although there are several that are apparently unique to some of these new drugs. Gabapentin has been reported to cause aggravation of seizures, movement disorders and psychiatric disturbances. Felbamate should only be prescribed under close medical supervision because of aplastic anaemia and hepatotoxicity. Lamotrigine causes hypersensitivity reactions that range from simple morbilliform rashes to multi-organ failure. Psychiatric ADRs and deterioration of seizure control have also been reported with lamotrigine treatment. Oxcarbazepine has a safety profile similar to that of carbamazepine. Hyponatraemia associated with oxcarbazepine is also a problem; however, it is less likely to cause rash than carbamazepine. Nonconvulsive status epilepticus has been reported frequently with tiagabine, although there are insufficient data at present to identify risk factors for this ADR. Topiramate frequently causes cognitive ADRs and, in addition, also appears to cause word-finding difficulties, renal calculi and bodyweight loss. Vigabatrin has been reported to cause seizure aggravation, especially in myoclonic seizures. There have been rare reports of other neurological ADRs to vigabatrin, such as encephalopathy, aphasia and motor disturbances. Vigabatrin-induced visual field constriction is the latest and most worrying ADR. Many questions regarding the nature of this potentially serious ADR remain unanswered, as no prospective controlled study examining the phenomenon has been published. Rare cases of behavioural ADRs and IgA and IgG2 deficiency associated with the use of zonisamide have been reported. However, relatively few patients so far have been exposed to this drug, and therefore more postmarketing information is required. The relatively late establishment of aplastic anaemia and hepatic failure as potentially fatal ADRs of felbamate, and of visual field constriction with vigabatrin, should serve as ample reminders that ADRs can appear at any time.

Enzyme induction and inhibition by new antiepileptic drugs: a review of human studies

The aim of this paper is to review a number of new antiepileptic agents (i.e. felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine, topiramate, vigabatrin and zonisamide) for their inducing and/or inhibitory properties in humans, mainly considering the interactions where they are involved as the cause rather than the object of such interactions. Two aspects have been particularly taken into account: the changes or absence of changes in plasma/serum concentrations of concomitant drugs and the direct or indirect evidence of induction, inhibition or lack of effect on the six major human hepatic CYP isozymes (CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1 and CYP3A4), as well as on other CYP isozymes or enzyme systems. Felbamate clearly affects the pharmacokinetics of a number of drugs, generally increasing but also decreasing their concentrations. It induces enzymes such as CYP3A4 and inhibits enzymes such as CYP2C19 and those of the beta-oxidation pathway. Topiramate is not devoid of potential interaction properties: it decreases the plasma concentrations of ethinylestradiol, induces CYP3A4 and inhibits CYP2C19. For oxcarbazepine, no inhibitory, only inductive effects have been observed thus far. Felbamate. topiramate and oxcarbazepine may induce the metabolism of steroidal oral contraceptives. In this respect, tiagabine has been studied at a rather low dose. Pharmacodynamic or pharmacokinetic interaction seems to exist between lamotrigine and carbamazepine. Lamotrigine appears to be a weak inducer of UGTs, whereas induction of CYP3A4 seems improbable as the compound does not change the concentrations of oral contraceptives or the urinary excretion of 6beta-hydroxycortisol. Zonisamide has very peculiar pharmacokinetics and an extensive metabolism. Additional information on its enzyme inducing or inhibiting properties would be necessary, as data so far collected on its effect on the pharmacokinetics of other drugs are conflicting. Gabapentin, vigabatrin and in particular levetiracetam appear to be devoid of significant enzyme inducing or inhibiting properties.

Vigabatrin as add-on therapy for adult complex partial seizures: a double-blind, placebo-controlled multicentre study. The Canadian Vigabatrin Study Group

Vigabatrin (VGB) is a novel antiepileptic drug effective as adjunctive therapy in patients with partial seizures. In this study, the efficacy and tolerability of VGB as adjunctive therapy were evaluated in patients with refractory epilepsy. Adult patients with a definite diagnosis of complex partial seizures and/or partial seizures secondarily generalized were recruited from 10 Canadian centres. Patients were randomized to receive either active medication or placebo in a double- blind fashion and entered a 36-week titration and maintenance phase with regularly scheduled visits. Both efficacy parameters and safety assessments were monitored. Clinical laboratory, evoked potential studies, MRI, and neuropsychological tests were also performed. Forty-eight percent of VGB-treated patients vs. 26 percent of placebo-treated patients had a 50 percent or greater reduction in the frequency of complex partial seizures and partial seizures secondarily generalized. Vigabatrin was well tolerated by the majority of patients. Minor neurological side effects were observed in a number of patients in both treatment groups. No serious systemic toxicity was observed. No changes in evoked potential studies or MRI findings were noted. Vigabatrin was found to be an effective and well-tolerated antiepileptic drug when used as adjunctive therapy in patients with difficult to control complex partial seizures and for partial seizures secondarily generalized. Vigabatrin is a selective irreversible inhibitor of the GABA- degradating enzyme GABA transaminase and has shown efficacy in a number of clinical trials in patients with difficult to control partial seizures. Vigabatrin has been found most effective against complex partial and secondarily generalized tonic-clonic seizures in both adults and children. Vigabatrin has also been shown to reduce infantile spasms secondary to various aetiologies and is most effective in spasms associated with tuberous sclerosis. The aim of this study was to further extend the clinical experience with VGB as adjunctive therapy in the treatment of adult patients with difficult to control complex partial seizures and/or partial seizures secondarily generalized. In addition to the assessments of efficacy and tolerability to VGB, neuropsychological evaluations were also carried out.

The potential for vigabatrin-induced intramyelinic edema in humans

PURPOSE

Vigabatrin (Sabril, Hoechst Marion Roussel) is an antiepilepsy drug (AED) presently marketed in 64 countries for the treatment of partial and secondarily generalized seizures. Vigabatrin (VGB) is marketed in a subset of these countries for the treatment of infantile spasms. Clinical experience in humans has shown that VGB provides effective seizure control with a wide margin of safety. However, animal toxicity studies raised concern when prolonged administration of VGB was shown to induce intramyelinic edema (IME) in some laboratory animal species.

METHODS

Animal and human data were reviewed with respect to the potential for VGB-induced IME. Surveillance of patients receiving VGB in clinical trials or by prescription has been conducted for >15 years to identify patients developing clinical abnormalities that might be IME related.

RESULTS

The histologic lesions of VGB-induced IME in animals are reliably reproduced and correlate with changes in multimodality evoked potentials (EPs) and magnetic resonance imaging (MRI). Numerous studies of the effects of VGB on EP and MRI in epilepsy patients have demonstrated no clear-cut IME-related changes in these modalities. Additionally, autopsy and surgical brain samples from VGB-treated patients have been scrutinized for potential IME histopathology. In an estimated 350,000 patient-years of VGB exposure (approximately 175,000 patients exposed for 2 years at an average dose of 2 g/day), no definite case of VGB-induced IME has been identified.

CONCLUSIONS

Comprehensive review of a variety of sources of data failed to identify any definite case of IME in humans treated with VGB.

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.

Vigabatrin

Vigabatrin (VGB) is a structural analogue of the inhibitory neurotransmitter gamma-amino butyric acid (GABA), which produces its antiepileptic effect by irreversibly inhibiting the degradative enzyme GABA-transaminase. This produces an increase in central nervous system (CNS) GABA levels. VGB is among the few antiepileptic drugs (AEDs) that was synthesized with a specific targeted mechanism in mind and was subsequently demonstrated to function by that mechanism. Tiagabine, a GABA reuptake blocker, is the only other "designer drug" among the currently available AEDs. Therefore, VGB is among the few AEDs for which the mechanism of action is well understood. Recently, safety issues have been raised with regard to the use of vigabatrin. This article reviews the mechanism of action, pharmacokinetics, safety, and efficacy of VGB.

Safety and efficacy of vigabatrin and carbamazepine in newly diagnosed epilepsy: a multicentre randomised double-blind study. Vigabatrin European Monotherapy Study Group

BACKGROUND

Vigabatrin is a newly licensed drug for use in patients with epilepsy. We investigated whether this drug was comparable to standard first-line monotherapy in efficacy and incidence of adverse events.

METHODS

We enrolled 459 patients with newly diagnosed, previously untreated partial epileptic seizures from 44 European centres and randomly assigned them carbamazepine 600 mg daily (n=230) or vigabatrin 2 g daily (n=229). After initial maintenance doses were reached, doses were adjusted downwards (in the case of adverse events) or upwards (in the case of seizures) by the clinician. The primary outcome was time to withdrawal because of lack of efficacy or adverse events. Secondary outcomes included efficacy (time to 6-month remission of seizures, time to first seizure after initial dose stabilisation), and adverse events (incidence and severity). Analysis was by intention to treat.

FINDINGS

Time to withdrawal for lack of efficacy or adverse events did not differ between groups (p=0.318). Vigabatrin was better tolerated than carbamazepine with fewer withdrawals, but was more frequently associated with psychiatric symptoms (58 [25%] vs 34 [15%]) and weight gain (25 [11%] vs 12 [5%]). Carbamazepine was associated with rash (22 [10%] vs seven [3%]). All efficacy outcomes favoured carbamazepine and failed to show equivalence between the two drugs. No significant difference was found for time to achieve 6 months of remission from seizures (p=0.058), but the most powerful outcome, time to first seizure after the first 6 weeks from randomisation, showed carbamazepine to be significantly more effective than vigabatrin (p=0.0001).

INTERPRETATION

Vigabatrin seems less effective but better tolerated than carbamazepine, which is the first-choice drug for the treatment of partial epilepsies. Vigabatrin cannot therefore be recommended as a first-line drug for monotherapy in this group of patients.

Vigabatrin in the treatment of infantile spasms

Infantile spasms (IS) have been conventionally treated with adrenocorticotropic hormone (ACTH), which is often associated with significant side effects. This study assessed the efficacy of vigabatrin (VGB) as an alternative in the treatment of IS and compared the efficacy of VGB in symptomatic vs cryptogenic patients. The study retrospectively reviewed 25 infants with IS (19 symptomatic, six cryptogenic) who were treated with VGB. Of the symptomatic group, 13 (68.4%) of 19 had clinical improvement, and 15 (78.9%) had electroencephalographic improvement. Three (50%) of six in the cryptogenic group had clinical improvement, and two (33%) had electroencephalographic improvement. Overall, three patients demonstrated clinical spasm control but electroencephalographic deterioration or persistence of hypsarrhythmia coupled with further cognitive decline. Four of the six partial clinical responders had deterioration of spasms with additional VGB dosage increases. VGB is comparable with ACTH in effectiveness for treatment of symptomatic IS. Higher doses of VGB may sometimes cause deterioration rather than further improvement, and therefore an optimum dosage of VGB needs to be titrated for every patient. Persistent electroencephalographic abnormalities and even electroencephalographic deterioration despite clinical control have been observed with VGB treatment; electroencephalographic monitoring during VGB treatment is recommended.

Reappraisal of polytherapy in epilepsy: a critical review of drug load and adverse effects

PURPOSE

We reviewed the literature to determine whether an analysis of published data could clarify the relationship between antiepileptic drug (AED) polytherapy and adverse affects (AE). We highlight the problems encountered.

METHODS

We made a Medline-search for articles published between 1974 and 1994 reporting the number of AE and doses or serum levels of every AED, per patient or treatment group, and used the PDD/DDD ratio to calculate AED load per patient from doses or the OSL/AToxL ratio to do so from serum levels of individual drugs. The PDD/DDD is the sum of ratios of the actual prescribed daily doses divided by the published average therapeutic dose of each drug. The OSL/AToxL is the sum of each observed serum level divided by its average toxic level.

RESULTS

We retrieved 118 trial reports. Most had to be excluded because of incomplete reporting of concomitant medication or AE. The data of the 15 articles selected for further analysis indicate a relationship between drug load and number of AE. We noted no relationship between the number of AEDs administered and AE. In add-on studies, the difference in neurotoxicity between the active and placebo arm may be obscured if the relative increase in drug load is small, as exemplified by the study of McGuire et al..

CONCLUSIONS

Articles reporting add-on trials of new AEDs generally do not provide detailed information about the basic medication to which the new AED is added, which makes calculation of total drug load impossible. Furthermore, often only frequency of AE is reported, not severity or development of tolerance, making it difficult to judge the impact of AE. However, despite the paucity of available information, we present some evidence that toxicity in AED polytherapy may be related to total drug load, rather than to the number of drugs administered. Therefore, the present trend to reject polytherapy for fear of increased toxicity is not warranted, which removes one of the objections to initiating specific research to prove or disprove the value of AED combinations as long as the drug load is appropriate.

Vigabatrin in partial seizures in children

Patients with partial seizures aged 1 week to 19 years (n = 175) were included in several prospective vigabatrin studies at the hospital Saint Vincent de Paul. A decrease in seizure frequency of over 50% was achieved in 70% of patients, with 30% becoming seizure free, and only 6% experiencing an increase. Tuberous sclerosis gave the best response (85%), tumors the lowest (45%), the usual figure for other causes being 70%. Patients with malformations were the most likely to experience seizure increase. Regarding topography of focus, the lowest rate of seizure-free patients was in rolandic foci. Early treatment produced better results. Infants experienced the highest rate of response, but also of relapse, the latter occurring mainly between 6 months and 1 year. The incidence of loss of efficacy depended on etiology and topography of focus, tumors and frontal foci having the highest risk. Occurrence of new seizures was more frequent in young patients with tuberous sclerosis, the third experiencing status epilepticus. Vigabatrin monotherapy could only be achieved in 33% of seizure-free patients, reduction of comedication being a risk of relapse and of further intractability.

No effect of long-term vigabatrin treatment on central nervous system conduction in patients with refractory epilepsy: results of a multicenter study of somatosensory and visual evoked potentials. PMS Study Multicenter Group

PURPOSE

In dogs, vigabatrin (VGB) has been associated with intramyelinic edema producing delayed central conduction in somatosensory and visual evoked potentials (SEP, VEP). No such effects have been reported in humans. We assessed whether abnormalities of central conduction could be detected prospectively in patients with epilepsy treated with VGB as long-term add-on medication.

METHODS

Two hundred one patients with refractory partial epilepsy were enrolled and monitored for as long as 2 years. VGB was added to the treatment at an average dose of 2-3g/day. Conduction in somatosensory and visual pathways was assessed by median nerve SEP and pattern VEP recordings performed at inclusion and once every 6 months. The upper limit and test-retest variability of EP latencies were evaluated at time of enrollment in the patient group. Prolonged N13-N20 or P14-N20 SEP intervals and P100 VEP latency >2.5 SD above the baseline mean, observed on repeated runs in the same session and exceeding the test-retest variability at enrollment were considered to indicate central conduction slowing.

RESULTS

One hundred nine patients completed the 2-year study period, and 92 discontinued VGB, of whom 37 were monitored with regard to EP until the end of the study. No consistent change in SEP or VEP was observed in the entire group during VGB treatment. The number of occasional EP values outside the baseline range in patients treated with VGB similar to that in patients whose VGB treatment had been discontinued.

CONCLUSIONS

We detected no evidence of changes in SEP and VEP attributable to altered neuronal conduction in the CNS during long-term VGB treatment.

Pharmacokinetic interactions of the new antiepileptic drugs

Therapy with traditional antiepileptic drugs is associated with a wide range of pharmacokinetic drug-drug interactions. In particular, enzyme induction, enzyme inhibition and displacement from protein binding may result in important changes in serum concentrations of antiepileptics. Relevant interactions have also been described for some new antiepileptics. Felbamate increases serum concentrations of phenytoin, phenobarbital and valproic acid (sodium valproate). On the other hand, it reduces concentrations of carbamazepine and increases concentrations of its metabolite carbamazepine-10,11-epoxide. Concentrations of felbamate itself are reduced by phenytoin and carbamazepine. Concentrations of lamotrigine are considerably increased by valproic acid and decreased by phenytoin, carbamazepine and phenobarbital (phenobarbitone). Vigabatrin reduces serum concentrations of phenytoin by approximately 20%. On the other hand, some new antiepileptics have the important advantage of not interfering with the metabolism of other antiepileptics; this is the case for gabapentin, lamotrigine and oxcarbazepine. Furthermore, the pharmacokinetics of gabapentin, oxcarbazepine and vigabatrin are independent of concomitant drugs. These aspects are especially important as, until now, new antiepileptics have been most often utilised as add-on therapy.

Influence of vigabatrin on cognitive performances and behaviour in patients with drug-resistant epilepsy

INTRODUCTION

The aim of this research was to evaluate changes in cognitive performances, mood and quality of life in drug-resistant epileptic patients, after the introduction of Vigabatrin (VGB) as additional treatment.

MATERIAL AND METHODS

A four-step evaluation was carried out in two groups of 20 patients each, randomly assigned to VGB or placebo treatment. A battery of neuropsychological tests investigating attention, memory and adaptive abilities, associated with inventories concerning depression, quality of life and the concern of families upon patient behaviour, were utilised. For each subject, four evaluations were performed, two before and two after VGB/placebo administration.

RESULTS

No relevant side-effects regarding cognition and behavior were detected in the VGB group. The intra-group comparison between pre- and post-treatment phases showed a slight improvement in cognitive performances of VGB patients and a positive change in their overall psychological status. The inter-group comparison confirmed the selective improvement occurring in the trend of a few neuropsychological test scores in the VGB group.

CONCLUSION

Such results help to reject the hypothesis that the addition of VGB to the current antiepileptic treatment may affect cognitive performances and behaviour.

Psychotic and severe behavioural reactions with vigabatrin: a review

Behavioural disturbances and psychotic reactions are commoner in patients with epilepsy than in the general population and may be precipitated by the majority of antiepileptic drugs, including the newer ones. These reactions may be more frequent in patients with complex partial seizures, reflecting underlying temporal lobe pathology. A review of the literature on vigabatrin found an incidence of severe abnormal behaviour in controlled trials in adults of 3.4%. In children open studies gave an incidence of around 6%. This may be related to dosage and speed of introduction. Such reactions may be related to changes in seizure control, either unaccustomed good control (force normalisation) or breakdown in control, implying non-specific causative mechanisms. Alternatively, any relationship to control may be fortuitous and specific, unknown pharmacological mechanisms may be involved. Appropriate risk reduction measures include slow introduction, limiting the dose to that required for seizure control, slow withdrawal and increased vigilance in those on polytherapy or with psychiatric histories. Such advice is pertinent to all antiepileptic medications. Additionally, vigabatrin is probably contraindicated in idiopathic generalised epilepsies. Behavioural reactions are uncommon with vigabatrin, and have not been shown to be greater with it than with other antiepileptic agents. Therefore, it maybe inappropriate to withhold the drug from those who may benefit from it.

Reduction of plasma alanine aminotransferase during vigabatrin treatment

In 9 drug-resistant patients with partial seizures treated with vigabatrin, gamma-vinyl GABA (VGB), alanine aminotransaminase (ALAT) activity in plasma was significantly reduced. Comparison of in vitro with in vivo measurements led us to conclude that this reduction is mainly an in vivo phenomenon, perhaps due to cross-enzyme inhibition. The assessment of two biological variables linked with ALAT, glucose and alanine levels under fasting conditions, failed to show any significant metabolic alterations. VGB is an effective drug for partial epilepsy. Our observations do not suggest that reduced ALAT activity is of clinical concern.

Retrospective study of vigabatrin and psychiatric behavioural disturbances

Vigabatrin (VGB) is an effective add-on anti-epileptic drug. The major serious adverse drug reactions (ADRs) are behavioural and psychiatric disturbances. This study does not support the view that a previous history of behavioural and psychiatric features increases the risk of behavioural/psychiatric ADRs (relative risk 1.23, 95% CI 0.57-2.66, P = 0.61). The results suggest that a low starting does of vigabatrin does not reduce the risk of psychiatric and behavioural ADRs (P = 0.31) or prevent a more overt psychotic reaction from occurring.

Vigabatrin

gamma-Aminobutyric acid (GABA) was first proposed as a putative inhibitory neurotransmitter by Elliot and van Gelder in 1958. Since then, numerous efforts have been made to find ways to increase GABA at its receptor sites, based on the findings that decreased GABA results in convulsions in animals and that agents enhancing GABA-mediated functions can have antiepileptic effects. However, the relationship between GABA levels and seizures is not simple. Seizures can occur even in the presence of elevated GABA levels. Indeed, it is possible that regional biochemical differences in the brain can be important. The antiepileptic effects of GABA depend on the mechanism whereby GABA-mediated inhibition is enhanced. Since the 1970s, several compounds have been developed that are designed to act in some manner on the GABA system. These compounds affect GABA-mediated inhibition at different levels and appear to have varied effects, depending on their mechanism of action. To date, specific antiepileptic drugs (AEDs) with potential GABA-inhibitory effects have been designed either to have GABA agonist properties, to inhibit GABA catabolism, to inhibit GABA uptake, or to facilitate GABA release or facilitate GABAA receptor activity. Vigabatrin (VGB) was designed specifically to inhibit GABA transaminase and thereby increase the availability of GABA in the brain. Study data and clinical experience over the past 14 years have demonstrated VGB to be an effective AED.

Development of myoclonus in patients with partial epilepsy during treatment with vigabatrin: an electroencephalographic study

In the context of a study of the effects of gamma-vinyl-GABA (GVG) on seizure occurrence and on EEG abnormalities we present three cases with focal epilepsy in which new clinical and EEG paroxysmal manifestations were observed during GVG therapy. At that time, whereas an amelioration or no change in patients' habitual seizures were observed, myoclonic jerks appeared with related changes in the EEG paroxysmal abnormalities, represented by generalized polyspike and wave complexes. An electroclinical correlation was recorded in one case. These data indicate that, although occurring rarely, it is possible to have epileptic myoclonus during GVG treatment. Mechanisms underlying these manifestations are difficult to explain. Probably a shift in the anti/proconvulsant GABAergic balance towards the latter may compromise the therapeutic effect of GVG.

New antiepileptic drugs for children: felbamate, gabapentin, lamotrigine, and vigabatrin

After a 15-year hiatus, several new antiepileptic drugs have been approved or are under Food and Drug Administration investigation for use in the United States. This article reviews four of these new drugs--felbamate, gabapentin, lamotrigine, and vigabatrin. Although these drugs have been primarily developed for use in adults with partial seizures, they will also likely be used in children with partial epilepsy. Pediatric experience with several of these drugs has demonstrated safety and efficacy in other seizure types and epilepsy syndromes. These drugs will be an important addition to the therapeutic armamentarium for pediatric epilepsy. Additional studies are needed to fully explore the safety and efficacy of these drugs in a variety of pediatric epilepsies and to compare them to existing antiepileptic drugs.

Vigabatrin

The discovery of gamma-aminobutyric acid (GABA) as the first major inhibitory neurotransmitter and a program exploring the use of enzyme inhibition as a therapeutic tool provided the basis for the conception of vigabatrin (VGB, Sabril). This molecule, an analogue of GABA, has a highly specific activity as an enzyme-activated irreversible inhibitor of GABA-transaminase causing several-fold increases in the concentration of brain GABA. In animal models for epilepsy, it was found to have a rather different spectrum of activity than conventional antiepileptic drugs (AEDs). The clinical development of VGB was delayed by the finding of focal areas of reversible microvacuolation in the white matter of the brains of rodents and dogs. An extensive human safety program has confirmed that this finding is species specific and does not occur in humans. Clinically, VGB is well tolerated and has been shown to be specially effective in the management of partial seizures that have failed to respond to other AEDs. In most controlled studies, about 50% of patients with previously uncontrolled seizures have a 50% reduction in frequency and about 4-5% become seizure-free. In children, it also appears to be especially effective in the management of infantile spasms as well as in partial seizures. VGB offers a significant improvement in the management of epilepsy and is now under development as a first-line agent.