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

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.

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.

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.

Antiepileptic drug-induced cognitive adverse effects: potential mechanisms and contributing factors

Cognitive dysfunction is frequently observed in patients with epilepsy and represents an important challenge in the management of patients with this disorder. In this respect, the relative contribution of antiepileptic drugs (AEDs) is of relevance. The fact that a considerable number of patients require AED therapy for many years, or perhaps even a lifetime, emphasizes the need to focus on the long-term adverse effects of these drugs on cognition. The most prevalent of the CNS adverse effects observed during AED therapy are sedation, somnolence, distractibility, insomnia and dizziness. Sedation, in particular, is associated with most of the commonly used AED therapies. Nevertheless, cognitive function in individuals with epilepsy may also be influenced by several factors, of which AEDs constitute only one of many putative causes. In general terms, most studies agree that some differences exist among the older AEDs with regard to the effects on cognition, and some newer generation molecules may have a better cognitive profile than older AEDs. The mechanisms of action are an obvious determinant; however, there is still a lack of evidence for differentiation between available drugs with regard to cognitive effects. Some authors have suggested that there may be different cognitive effects associated with individual drugs; however, the question as to whether there are more specific deficits related to the action of individual drugs remains unsolved. There seems to be agreement that polytherapy and high-dose treatment can produce cognitive adverse effects and when high dosages or adjunctive polytherapy is needed, the balance between benefits and disadvantages may be negatively biased against drug treatment. Thus, drug treatment requires careful balancing in the attempt to reach maximal seizure control while avoiding neurotoxic adverse effects. Finally, the mood status of the patient and clinical relevance of the information obtained by neuropsychological testing represent important variables that need to be taken into account when discussing cognitive adverse effects of AEDs.

The aspects and mechanisms of cognitive alterations in epilepsy: the role of antiepileptic medications

Epilepsy is a major health problem. Several studies suggest a significant influence of epilepsy and its treatment on dynamic and functional properties of brain activity. Epilepsy can adversely affect mental development, cognition, and behavior. Epileptic patients may experience reduced intelligence, attention, and problems in memory, language, and frontal executive functions. Neuropsychological, functional, and quantitative neuroimaging studies revealed that epilepsy affect the brain as a whole. Mechanisms of epilepsy-related cognitive dysfunction are poorly delineated. Cognitive deficits with epilepsy may be transient, persistent, or progressive. Transient disruption of cognitive encoding processes may occur with paroxysmal focal or generalized epileptic discharges, whereas epileptogenesis-related neuronal plasticity, reorganization, sprouting, and impairment of cellular metabolism are fundamental determinants for progressive cognitive deterioration. Also antiepileptic drugs (AEDs) have differential, reversible, and sometimes cumulative cognitive adverse consequences. AEDs not only reduce neuronal irritability but also may impair neuronal excitability, neurotransmitter release, enzymes, and factors critical for information processing and memory. The present article serves as an overview of recent studies in adult and childhood epilepsy literatures present in PubMed that highlighted cognitive evaluation in epilepsy field (publications till 2008 were checked). We also checked the reference lists of the retrieved studies for additional reports of relevant studies, in addition to our experience in this field. Our search revealed that although the aspects of cognitive dysfunction, risk factors, and consequences have been explored in many studies; however, the mechanisms of contribution of epilepsy-related variables, including AEDs, to patients' cognition are largely unexplored. In this review, we discussed the differential effect of AEDs in mature and immature brains and the known mechanisms underlying epilepsy and AEDs adverse effects on cognition. The nature, timing, course, and mechanisms of cognitive alteration with epilepsy and its medications are of considerable clinical and research implications.

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.

Pharmacological and behavioral characteristics of interactions between vigabatrin and conventional antiepileptic drugs in pentylenetetrazole-induced seizures in mice: an isobolographic analysis

To characterize the anticonvulsant effects and types of interactions exerted by mixtures of vigabatrin (VGB) and conventional antiepileptic drugs (valproate (VPA), ethosuximide (ESM), phenobarbital (PB), and clonazepam (CZP)) in pentylenetetrazole (PTZ)-induced seizures in mice, the isobolographic analysis for three fixed-ratio combinations of 1 : 3, 1 : 1, and 3 : 1 was used. The adverse-effect profile of the combinations tested, at the doses corresponding to their median effective doses (ED(50)) at the fixed-ratio of 1 : 1 against PTZ-induced seizures, was determined by the chimney (motor performance), step-through passive avoidance (long-term memory), pain threshold (pain sensitivity), and Y-maze (general explorative locomotor activity) tests in mice. Additionally, the observed isobolographic interactions were verified in terms of a pharmacokinetic interaction existence. VGB combined with PB or ESM exerted supra-additive (synergistic) interactions against the clonic phase of PTZ-induced seizures, which was associated with the increment of PB or ESM concentrations in the brains of examined animals. The remaining combinations tested (ie VGB+VPA and VGB+CZP) occurred additive in the PTZ test, which was associated with no significant changes in the brain concentrations of VPA and CZP. None of the examined combinations exerted motor impairment in the chimney test in mice. In the standard variant of passive avoidance task (current of 0.6 mA; 2 s of stimulus duration), the combinations of VGB+CZP and VGB+VPA significantly affected long-term memory in mice. Moreover, VGB in a dose-dependent manner lengthened the latency to the first pain reaction in the pain threshold test in mice. The modified variant of step-through passive avoidance task (current of 0.6 mA; stimulus duration based on the latency from the pain threshold test) revealed no significant changes in the long-term memory of animals for the combinations of VGB+VPA and VGB+CZP; so the observed effects in the standard variant of passive avoidance task were a result of the antinociceptive effects produced by VGB. In the Y-maze test, VGB also, in a dose-dependent manner, increased the general explorative locomotor activity of the animals tested. Similarly, the total number of arm entries in the Y-maze was significantly increased for the combinations of VGB+CZP and VGB+ESM, but not for VGB+PB and VGB+VPA. The application of VGB in combination with PB, ESM, CZP, and VPA suppressed the clonic phase of PTZ-induced seizures, having no harmful or deleterious effects on behavioral functioning of the animals tested, which might be advantageous in further clinical practice.

Health-related quality of life in senior adults with epilepsy: what we know from randomized clinical trials and suggestions for future research

OBJECTIVE

The goal of this work was to review the randomized controlled trial (RCT) literature on antiepileptic medication effects on health-related quality of life in seniors with epilepsy.

METHODS

Studies published from 1998 to June 2002 were identified by searching through Medline and the Cochrane Clinical Trials Register. Pre-1998 RCTs identified by Baker et al. [Epilepsia 41 (2003) 1357] were also examined for relevance to the present review. Studies were reviewed if they included a RCT design and included epilepsy patients over the age of 60.

RESULTS

A total of 85 clinical trials were reviewed. Of the 85 studies reviewed only 37 RCT studies included patients over the age of 60. However, formal quality-of-life outcome assessment was not performed in any of the RCTs that included senior adults, and only six studies provided formal quantitative analyses of AED effects in the form of adverse events incidence and participant withdrawal rates. For the most part, early study withdrawal rates were substantial for seniors and adverse events were very common. Two studies reporting on the cognitive and behavioral effects of study AEDs indicated only modest impact when AED monotherapy was kept at therapeutic levels.

CONCLUSIONS

Despite growing appreciation for quality-of-life, issues in the management of epilepsy little current empirical guidance is available for elderly with epilepsy. There exists virtually no information on elderly patient preferences and goals for epilepsy treatment outcomes, and available data primarily concerns younger adults. Despite some encouraging preliminary evidence from this review suggesting that conservative AED treatment may have a more favorable quality of life-related outcome, more conclusive statements await further systematic investigation.

Effect of antiepileptic drugs on cognitive function in individuals with epilepsy: a comparative review of newer versus older agents

Several 'new' antiepileptic drugs (AEDs), i.e. oxcarbazepine, vigabatrin, lamotrigine, zonisamide, gabapentin, tiagabine, topiramate and levetiracetam have been introduced into clinical practice within the last decade. Most of these new drugs are at least as effective as the 'old' AEDs [phenytoin, phenobarbital (phenobarbitone), valproic acid (sodium valproate) and carbamazepine] and, in general, they seem to be better tolerated than the old drugs. The new AEDs might have less influence on cognitive functions but the aspect has not been systematically studied. Neuropsychological testing has been the major method of objectively examining cognitive function related to the use of AEDs but a number of methodological problems blur the results. Alteration of cognition might reflect a chronic adverse effect of AEDs but the negative effects of the drugs are only one of several factors that may influence cognition. In addition, subjective complaints about cognitive deficits (e.g. memory problems or attention) may also reflect other aspects of adverse effects than those concerning specific cognitive functions (e.g. mood and anxiety). This review focuses on studies of the cognitive effects of the new AEDs, and in particular on studies that compare cognitive effects of the old and new drugs. In general, the new AEDs seem to display no or minor negative cognitive effects. In studies in which new AEDs have been compared with old AEDs, there was a tendency in favour of the new AEDs in some of the studies.

Behavioural effects of the new anticonvulsants

Of the 9 new anticonvulsants that have been marketed recently in the UK or US, a number appear to have either adverse or beneficial effects on behaviour. There is now a considerable database of information, in terms of the number of patients treated and/or the number of published reports, on vigabatrin, lamotrigine, gabapentin and topiramate. Oxcarbazepine has been available in some centres for several years and there is extensive experience with the drug in Scandinavia. It appears that the profile of adverse and beneficial effects is similar to that of carbamazepine. Behavioural effects have probably been greatest with vigabatrin, with psychosis, depression and other behavioural problems recorded, but the use of this drug has been limited because of the concern about visual field constriction. The cognitive and behavioural effects of topiramate have caused concern, but these may be much less of a problem if lower starting dosages and escalation rates are used. Psychosis and depression have been associated with topiramate, as they have with another carbonic anhydrase inhibiting drug, zonisamide. Although zonisamide has been used for many years in Japan and Korea, experience elsewhere with this drug is currently very limited. Gabapentin seems to be less associated with adverse behavioural effects than some of the other new anticonvulsant drugs. The reports of behavioural disturbance with gabapentin in children may be related to dose escalation. Behavioural disturbance as a direct result of lamotrigine seems to be uncommon, although indirect effects on behaviour, through the so-called 'release phenomenon' from improved seizure control and consequent ability to misbehave, can occur. Positive behavioural effects have been described with several of the new anticonvulsants, particularly gabapentin, lamotrigine and oxcarbazepine; all of these drugs may have mood-levelling effects that could be of value in treating affective disorders. The information on tiagabine and levetiracetam is too limited to allow any firm conclusions to be drawn with regard to positive or negative behavioural effects. When interpreting reports of behavioural changes with anticonvulsants, it is important to avoid attributing the effect to the drug when one or more of the other multiple causes of behavioural disturbance in people with epilepsy may be responsible or when an indirect effect such as 'forced normalisation' may be the cause. Many of the published studies are retrospective and unblinded rather than double-blind, placebo-controlled, prospective trials, implying that much of the data must be interpreted with caution at this stage.

Neuropsychological effects of epilepsy and antiepileptic drugs

Epilepsy and its treatment can have deleterious cognitive and behavioural consequences. Affected individuals have a higher prevalence of neuropsychological dysfunction than the general population because of complex interactions among several multifaceted and overlapping influences--for example, underlying neuropathologies, ictal and interictal neuronal discharges, a plethora of antiepileptic drugs, and numerous psychosocial issues. Research into the clinical relevance of these factors has been dogged by a range of methodological pitfalls including lack of standardisation of neuropsychological tests, small numbers and multiple testing, and statistical failure to appreciate differential effects of interactive elements in individual patients. Although antiepileptic drugs can impair neuropsychological functioning, their positive effect on seizure control might improve cognition and behaviour. Each person should be assessed individually with respect to factors unique to his or her seizure disorder and its treatment.

Quality-of-life and behavioral outcome measures in randomized controlled trials of antiepileptic drugs: a systematic review of methodology and reporting standards

PURPOSE

To review the methodology and use of quality-of-life and behavioral measures used in randomized controlled trials (RCTs) of antiepileptic drugs in patients with epilepsy.

METHODS

Trial reports were found by searching a previously developed comprehensive database of epilepsy RCTs and searching through journals by hand. Inclusion and exclusion criteria were applied, and methodological and quality-of-life and behavioral measure data were extracted.

RESULTS

There were 52 different measures used in 46 trials, with the Profile of Mood States, the Minnesota Multiphasic Personality Inventory, and the Washington Psychosocial Seizure Inventory being applied the most frequently. Overall, evidence of the reliability, validity, and sensitivity of measures used in populations of people with epilepsy was sparse. There was also little information on the clinical interpretation of the results.

CONCLUSION

Our results highlight a consistent failure to apply quality-of-life and behavioral measures in RCTs in a systematic way. We found repeated evidence of researchers' failure to review the use of previous measures and selection of measures without evidence of their appropriateness for use in a population with epilepsy. We recommend the use of quality-of-life and behavioral measures in RCTs with proven psychometric properties in a population with epilepsy.

Newer anticonvulsants: comparative review of drug interactions and adverse effects

The tolerability and drug interaction profiles of 6 new anticonvulsants: oxcarbazepine, vigabatrin, lamotrigine, gabapentin, tiagabine and topiramate, are reviewed. In general, these new anticonvulsants are well tolerated and drug interaction problems are minor with the exception of the risk of failure of oral contraceptives during treatment with oxcarbazepine or topiramate. In this review, the clinical implications of the tolerability of these drugs are discussed for different patient groups. The choice of which new anticonvulsant for which patient depends upon individual factors, in particular, seizure type, tolerability and practical administration factors. Treating elderly patients may be complicated by an increased sensitivity to adverse effects as these patients very often receive polytherapy for accompanying diseases. Drugs with very simple pharmacokinetic properties may be preferred in this group. Women of childbearing age face specific problems related to the epilepsy and to treatment with anticonvulsants. These include impaired fertility, failure of oral contraceptives and the risk of birth defects. Some new anticonvulsants may be suggested in preference to classical drugs to avoid these problems, but the human experience with newer anticonvulsants is still limited and, therefore, so is knowledge of the risk of congenital malformations in the offspring of mothers taking anticonvulsants. Psychiatric and behavioural changes frequently complicate treatment of patients with mental retardation. Some of the new anticonvulsants, in particular those affecting the gamma-aminobutyric acid (GABA) system such as vigabatrin, seem to exacerbate this problem and should be used with caution in these patients.

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.

New drugs for epilepsy

Seizure freedom with no side-effects is the aim of treatment, and new antiepileptic drugs have not lived up to expectations; only a few patients with chronic epilepsy have been rendered seizure-free. These treatments have side-effects but their safety profile may be better than older alternatives, although chronic effects have not yet been established. This article reviews newly marketed antiepileptic drugs. It concentrates on shortcomings of current antiepileptic treatment and on the way drugs are developed. A new approach to treatment is long overdue. The development of rational antiepileptic treatments should be strongly encouraged. More clinically relevant paradigms need to be developed and incorporated into clinical trial programmes as these are presently biased in their designs towards regulatory issues.