Vigabatrin and behaviour disturbance

Genetic association studies of glutamate, GABA and related genes in schizophrenia and bipolar disorder: a decade of advance

Schizophrenia (SZ) and bipolar disorder (BD) are debilitating neurobehavioural disorders likely influenced by genetic and non-genetic factors and which can be seen as complex disorders of synaptic neurotransmission. The glutamatergic and GABAergic neurotransmission systems have been implicated in both diseases and we have reviewed extensive literature over a decade for evidence to support the association of glutamate and GABA genes in SZ and BD. Candidate-gene based population and family association studies have implicated some ionotrophic glutamate receptor genes (GRIN1, GRIN2A, GRIN2B and GRIK3), metabotropic glutamate receptor genes (such as GRM3), the G72/G30 locus and GABAergic genes (e.g. GAD1 and GABRB2) in both illnesses to varying degrees, but further replication studies are needed to validate these results. There is at present no consensus on specific single nucleotide polymorphisms or haplotypes associated with the particular candidate gene loci in these illnesses. The genetic architecture of glutamate systems in bipolar disorder need to be better studied in view of recent data suggesting an overlap in the genetic aetiology of SZ and BD. There is a pressing need to integrate research platforms in genomics, epistatic models, proteomics, metabolomics, neuroimaging technology and translational studies in order to allow a more integrated understanding of glutamate and GABAergic signalling processes and aberrations in SZ and BD as well as their relationships with clinical presentations and treatment progress over time.

CNS adverse events associated with antiepileptic drugs

A variety of newer antiepileptic drugs (AEDs) are now available for treating patients with epilepsy in addition to the 'conventional' drugs that have been available throughout a large part of the last century. Since these drugs act to suppress the pathological neuronal hyperexcitability that constitutes the final substrate in many seizure disorders, it is not surprising that they are prone to causing adverse reactions that affect the CNS.Information on adverse effects of the older AEDs has been mainly observational. Equally, whilst the newer drugs have been more systematically studied, their long-term adverse effects are not clearly known. This is illustrated by the relatively late emergence of the knowledge of visual field constriction in the case of vigabatrin, which only became known after several hundred thousand patient-years of use. However, older drugs continue to be studied and there has been more recent comment on the possible effect of valproate (valproic acid) on cognition following exposure to this drug in utero.With most AEDs, there are mainly dose-related adverse effects that could be considered generic, such as sedation, drowsiness, incoordination, nausea and fatigue. Careful dose titration with small initial doses can reduce the likelihood of these adverse effects occurring. Adverse effects such as paraesthesiae are more commonly reported with drugs such as topiramate and zonisamide that have carbonic anhydrase activity. Weight loss and anorexia can also be peculiar to these drugs. Neuropsychiatric adverse effects are reported with a variety of AEDs and may not be dose related. Some drugs, such as carbamazepine when used to treat primary generalized epilepsy, can exacerbate certain seizure types. Rare adverse effects such as hyperammonaemia with valproate are drug specific. There are relatively very few head-to-head comparisons of AEDs and limited information is available in this regard.In this review, we discuss the available literature and provide a comprehensive summary of adverse drug reactions of AEDs affecting the CNS.

Consensus statement: the evaluation and treatment of people with epilepsy and affective disorders

Affective disorders in people with epilepsy (PWE) have become increasingly recognized as a primary factor in the morbidity and mortality of epilepsy. To improve the recognition and treatment of affective disorders in PWE, an expert panel comprising members from the Epilepsy Foundation's Mood Disorders Initiative have composed a Consensus Statement. This document focuses on depressive disorders in particular and reviews the appearance and treatment of the disorder in children, adolescents, and adults. Idiosyncratic aspects of the appearance of depression in this population, along with physiological and cognitive issues and barriers to treatment, are reviewed. Finally, a suggested approach to the diagnosis of affective disorders in PWE is presented in detail. This includes the use of psychometric tools for diagnosis and a stepwise algorithmic approach to treatment. Recommendations are based on the general depression literature as well as epilepsy-specific studies. It is hoped that this document will improve the overall detection and subsequent treatment of affective illnesses in PWE.

Diagnosis and management of depression and psychosis in children and adolescents with epilepsy

The neurologic dysfunction underlying epilepsy can predispose patients to psychiatric disorders, and the incidence of both depression and psychosis is increased in people with epilepsy. Depressive disorders are the most frequently recognized psychiatric comorbidities in people with epilepsy, but depression in children can be particularly difficult to recognize. Clinicians need to inquire about not only classic symptoms of depression such as anhedonia but also less obvious symptoms such as unprovoked irritability, unsubstantiated complaints of lack of love from family members, somatic complaints, and problems with concentration and poor school performance. The diagnosis of depressive disorders in children with epilepsy and mental retardation is even more difficult. Physicians need to be alert for the presence of iatrogenic depression, which may result from antiepileptic drugs or epilepsy surgery. People with epilepsy are also at increased risk for psychosis, which can be interictal, postictal, or (rarely) an expression of ictal activity. This psychosis can be related to seizure remission (ie, alternative psychosis) or iatrogenic (eg, related to antiepileptic drugs or following temporal lobectomy). Although both antidepressants and antipsychotic drugs have the potential to lower the seizure threshold and increase seizures, careful drug selection, dosing, and slow titration can minimize this risk, allowing treatment to proceed.

Depression in epilepsy: a frequently neglected multifaceted disorder

Depressive disorders (DDs) are frequent psychiatric comorbidities of neurological disorders like multiple sclerosis, stroke, dementia, migraine, Parkinson's disease, and epilepsy. The clinical manifestations of DDs in these neurological disorders are identical to those of idiopathic mood disorders. In epilepsy, however, DDs can frequently also present with clinical characteristics that differ from those of idiopathic depression and fail to meet the criteria included in the Diagnostic and Statistical Manual of Psychiatric Disorders-Fourth Edition. Despite their multifaceted clinical expressions and their relatively high prevalence in epilepsy, DDs very often go unrecognized and untreated. The aim of this article is to review some of the more relevant aspects of DDs in epilepsy, to highlight their various clinical expressions, and their impact on the quality of life of patients with epilepsy, and to review the basic principles of treatment.

Depression in epilepsy: prevalence, clinical semiology, pathogenic mechanisms, and treatment

Depression is the most frequent comorbid psychiatric disorder in epilepsy. Its lifetime prevalence has been estimated at between 6% and 30% in population-based studies and up to 50% among patients followed in tertiary centers. The risk of suicide has been estimated to be 10 times higher than that in the general population. Although no one questions that epilepsy is a risk for depression, recent studies have also revealed that a history of depression is associated with a 4- to 6-fold greater risk of developing epilepsy. These data suggest either a possible "bi-directional" relationship between these two disorders or the presence of common pathogenic mechanisms that facilitate the occurrence of one in the presence of the other. The clinical presentation of depressive disorders in epilepsy can be identical to that of nonepileptic patients and can include major depression, bipolar and dysthymic disorders, and minor depression. In a significant percentage of cases, however, the clinical features of depression in epilepsy fail to meet any of the DSM-IV Axis I categories. Depression in epilepsy may be iatrogenically induced with various antiepileptic drugs used to treat the seizure disorder or after surgical treatment of intractable epilepsy. Despite its relatively high prevalence, depression remains unrecognized and untreated, and unfortunately its treatment is based on empirical and uncontrolled data.

Psychiatric comorbidity in patients with developmental disorders and epilepsy: a practical approach to its diagnosis and treatment

Psychiatric comorbidity in patients with developmental disorders and epilepsy (PDDEs) is relatively frequent. The majority of its pharmacological treatment has consisted of the use of neuroleptic drugs in an attempt to control behavioral disturbances, despite the fact that these symptoms may often mask underlying psychiatric disorders such as anxiety and depression, which require other types of psychotropic drugs. In this article, we review the pathogenic mechanisms that mediate the clinical manifestations of psychiatric disorders in PDDEs, highlight diagnostic strategies that may help in elucidating the correct psychiatric diagnosis, and review the psychopharmacological treatments available.

Neuropsychiatric complications of epilepsy

Psychiatric complications of epilepsy are multiple and result from the complex interaction between endogenous, genetic, therapeutic, and environmental factors. The relationship between epilepsy and psychiatric disorders may be much closer than previously appreciated. Recent studies have suggested the existence of a bi-directional relationship between depression and epilepsy, whereby patients with epilepsy have a higher risk than the general population of suffering from depression, not only after, but also before the onset of epilepsy. Furthermore, similar neurotransmitter changes have been identified in depression and epilepsy, suggesting the possibility that these two disorders share common pathogenic mechanisms. Although the clinical manifestations of psychiatric disorders in epilepsy are often indistinguishable from those of nonepileptic patients, certain types of depression and psychotic disorders may present with clinical characteristics that are particular to epilepsy patients. These include the psychosis of epilepsy, postictal psychotic disorders, alternative psychosis (or forced normalization), and certain forms of interictal depressive disorders.

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.

Blockade of latent inhibition following pharmacological increase or decrease of GABA(A) transmission

The latent inhibition (LI) phenomenon refers to the retardation in learning of an association between a stimulus and a consequence if that stimulus had been previously experienced without consequence. An earlier study demonstrated that the benzodiazepine receptor agonist chlordiazepoxide (CDP), when administered before the phase of preexposure to the to-be-conditioned stimulus, impaired animals' ability to develop LI. The present study was designed to investigate the effect of the anxiogenic drugs pentylenetetrazole (PTZ) and the benzodiazepine partial inverse agonist Ro15-4513 on LI. Both anxiogenics, in contrast to CDP, are known for their GABA inhibitory action. The effects produced by the combined administration of a GABAergic function facilitator and inhibitor (CDP/PTZ and CDP/Ro15-4513) were also investigated. Both anxiogenic drugs led to an attenuation of LI, and, similarly to CDP, this attenuation was exclusively due to their administration prior to the preexposure stage of the experiment. However, this effect was abolished when anxiolytic and anxiogenic drugs were administered together, suggesting a pharmacological rather than behavioral summation of effects. These data also demonstrate the bidirectional GABAergic modulation of the LI phenomenon: both increased and decreased GABA(A) receptor activation led to reduced LI, thereby suggesting that an optimal receptor activation level is necessary for the normal establishment of LI.

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.

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.

Depression in epilepsy: a common but often unrecognized comorbid malady

Depressive disorders (DDs) represent the most frequent psychiatric comorbidity in epilepsy (1-5). Despite their relatively high prevalence, DDs remain unrecognized and untreated in many patients with epilepsy. The purpose of this review is to examine the reasons behind the failure to recognize and treat DDs in epilepsy. We highlight the essential epidemiologic, etiopathogenic, and clinical aspects that need to be considered in the evaluation of every epileptic patient and dedicate the last section of this paper to the review of the most relevant treatment issues. If we are successful in our goals, the reader will be impressed by the significant impact of DDs on the quality of life of these patients, and by the need to investigate treatment modalities with the same scientific rigor used in the assessment of efficacy of antiepileptic drugs in the control of seizures.

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.

Vigabatrin use in psychotic epileptic patients: report of a prospective pilot study

OBJECTIVES

Evaluation of any possible behavioural reactions in epileptic patients during vigabatrin treatment.

MATERIAL AND METHODS

Ten patients with refractory partial epilepsy, previous mental retardation and psychosis or other significant psychiatric morbidity treated with vigabatrin were submitted periodically to specific tests (to quantify any possible change in behavioural parameters) and also to EEG recordings.

RESULTS

After 1 year of treatment 5/10 patients became seizure-free, 3/10 of them presented reduction of seizures by over 75%. None of the subjects presented episodes that could be interpreted as psychotic reactions and, moreover, some patients showed a reduction in stereotypies, instability and aggressiveness. In 66% of these patients an improvement in cognitive functions was observed.

CONCLUSION

The onset of side effects can be prevented by a gradual introduction of vigabatrin and by the use of the drug in moderate doses. These data do not confirm the contraindication to treat with vigabatrin patients with a history of psychiatric disturbances.

Multicentre clinical evaluation of vigabatrin (Sabril) in mild to moderate partial epilepsies. French Neurologists Sabril Study Group

Vigabatrin (VGB) has been shown through several studies to be safe and effective as add-on therapy, particularly for the treatment of partial seizures in patients with severe epilepsies followed for years in hospital-based clinics. We now report additional clinical experience with VGB arising from an open trial of add-on VGB therapy in patients with relatively few seizures followed by qualified neurologists in private practice (the French Neurologists Sabril Study Group). VGB was administered to 397 patients aged 12-74 years (mean age = 37.5 +/- 13.8 years) who presented with no more than seven partial seizures of any type per month during a 3-month baseline period (mean number of seizures = 3.7 +/- 1.9/month). Simple partial seizures were reported in 121 (30.5%) patients, complex partial seizures in 282 (71.0%) and seizures with secondary generalization were reported in 111 (28.0%). The mean number of associated antiepileptic drugs (AEDs) was 1.9 +/- 0.9 and the mean dose of VGB was 2.21 +/- 0.64 g/day. Following introduction of VGB, 53 (13.4%) became seizure-free and remained so during the whole trial. During the fourth month of treatment, 158 patients (39.8%) had no seizures at all and a further 69 (17.4%) had their seizure frequency reduced by more than 50%. Secondary generalization was controlled during the whole period of treatment in 55 out of 97 patients (56.7%), 17 of which remained free of all types of partial seizures. VGB showed a good tolerability profile; adverse experiences more frequently reported were drowsiness and sleep disturbances. No action was necessary in the great majority of cases; the dose was reduced in 26 (6.5%) and VGB was discontinued in 32 (8%) patients. These data provide additional evidence that VGB can be used safely early on to treat patients with mild to moderate partial epilepsies. Secondary generalization was controlled in the majority of patients. Factors associated with the everyday clinical use of VGB, that resulted from a series of organized meetings with the investigators, are discussed.

Vigabatrin and behaviour disorders: a retrospective survey

Vigabatrin is an anticonvulsant drug with a relatively favourable side-effect profile. However, in clinical trials behaviour disorders have been reported, including agitation, depression and psychoses. In this study, 136 cases of behavioural problems that had been reported to the manufacturers, or the authors, were followed up. Satisfactory clinical information could be obtained on 81 patients. Of these, 50 cases met the criteria for either a psychosis (n = 28) or depression (n = 22). These were compared with a group of Queen Square patients, with epilepsy and psychosis, who had never taken vigabatrin (n = 21) and another group, who received vigabatrin without experiencing any behavioural problems (n = 28). The main results from this study suggest that: (1) Psychosis as a treatment emergent effect of vigabatrin is seen in patients with more severe epilepsy, compared with those patients who never develop psychopathology, and those developing an affective disorder. The psychosis is related to a right-sided EEG focus, and suppression of seizures (64% became seizure free). (2) Depression as a treatment emergent effect of vigabatrin is associated with a past history of depressive illness. There was little or no change in seizure frequency is this group. Some suggestions for managing patients who may develop these behaviour disorders are given.

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.

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.

Vigabatrin: effects on human brain GABA levels by nuclear magnetic resonance spectroscopy

Vigabatrin (VGB, Sabril) is a new antiepileptic drug used for treatment of partial and secondarily generalized tonic-clonic seizures. Many controlled short- and long-term trials have established efficacy as add-on therapy. Side effects have been infrequent. VGB acts as an irreversible substrate for gamma-aminobutyric acid (GABA) transaminase that leads to elevated brain GABA levels. Although this mechanism has been confirmed in animals and in cerebrospinal fluid of humans, we report the first study of brain GABA levels using noninvasive nuclear magnetic resonance spectroscopy. GABA elevation in brain closely parallels VGB dosage and reaches concentrations 2-3 times control values at daily dosage of 3 g. This technique offers promising potential to monitor changes induced by VGB as a function of time, dose, and clinical effect.

Vigabatrin use in 72 patients with drug-resistant epilepsy

OBJECTIVE

To determine the efficacy of a new anti-epileptic medication vigabatrin in adults and children with drug-resistant epilepsy.

DESIGN AND SETTING

An open, uncontrolled study in a tertiary referral clinic setting with vigabatrin used as add-on therapy.

SUBJECTS

All persons with intractable epilepsy, predominantly with complex partial seizures, with or without secondary generalization.

MAIN OUTCOME MEASURES

Outcome was assessed by the patient and physician in terms of reduction of seizure frequency and severity balanced against drug side effects.

RESULTS

Of 72 patients studied, seven are seizure-free and a total of 41/72 (57%) continue to take vigabatrin as they are deriving benefit therefrom. The results were most striking in patients with complex partial seizures with, or without, secondary generalization (65.6 and 60.9% ongoing treatment, respectively). Most of the 31 patients who ceased taking vigabatrin did so due to a lack of effect, but 9/31 did so because of adverse events: behavioural change, increased seizure frequency and oedema.

CONCLUSIONS

Vigabatrin has a definite role to play in the management of persons with intractable complex partial seizures where standard anti-epileptic therapy has failed to achieve control.

Gamma-vinyl GABA (vigabatrin) and mood disturbances

We explored factors that may predispose patients to adverse mood effects during treatment with vigabatrin (gamma-vinyl GABA; VGB): mood disorders before VGB treatment, type of epilepsy, seizure type and seizure frequency, type and number of comedication, and VGB dose. The clinical relevance of such a study is that it may help identify circumstances in which VGB should be administered with caution. Seventy-three patients (40 males, 33 females), all with refractory epilepsies, who received VGB as add-on therapy, were assessed by the Amsterdamse Stemmingslyst (ASL), a mood-rating scale, before the start of treatment, and demographic and clinical data were recorded. The patients were followed for 6 months after the start of VGB treatment. Treatment with VGB had to be discontinued in 38 patients (52% of the total sample). Mood problems were the main reason for discontinuation in 9 (12.3% of the total sample). In 6 other patients, mood problems were mentioned as the reason for discontinuing treatment, in combination with lack of drug efficacy. Development of adverse mood effects could not be predicted by a specific mood profile on the ASL. Before treatment, the "mood problems discontinuation group" did not show extreme scores for any assessed areas of mood and no significant differences from other patients were noted on the mood scales. Neither did clinical or demographic data show statistically confirmed specific characteristics for the mood problems discontinuation group, though the patients tended to use more antiepileptic drugs (AEDs) as cotherapy, to have a slightly lower daily dose of VGB, to be slightly older, and were mostly female.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of vigabatrin on partial seizures and cognitive function

Forty five patients with refractory partial seizures were studied in a prospective, randomised, placebo controlled, add on, parallel group, double blind trial of the new antiepileptic drug vigabatrin (1.5 g twice daily) followed by open treatment. Seizure frequency was monitored throughout an eight week baseline, 20 weeks double blind, and up to 18 months of open vigabatrin treatment. Cognitive function, including measures of memory and concentration, mood, and behaviour were assessed at baseline and again during the 20th week of treatment. Vigabatrin was associated with a significant reduction in a measure of motor speed and overall score on a design learning test in the first 20 weeks of treatment. In comparison with the baseline period, vigabatrin treatment was associated with a significant reduction in median complex partial seizure frequency four to 12 and 12 to 20 weeks after commencing vigabatrin (-66% and -69% in the vigabatrin group, +50% and +25% in the placebo group). Ten of 20 patients on vigabatrin and four of 23 on placebo showed a > 50% reduction in complex partial seizure frequency in the last eight weeks of double blind treatment. At least 60% of responders had maintained the response to vigabatrin when assessed during the open phase of the trial at 44 weeks. Two patients discontinued vigabatrin because of depression, which resolved on drug withdrawal.

Newer antiepileptic drugs. Towards an improved risk-benefit ratio

Epilepsy is one of the most common neurological disorders. Even though existing antiepileptic drugs can render 80% of newly diagnosed patients seizure free, a significant number of patients have chronic intractable epilepsy causing disability with considerable socioeconomic implications. There is, therefore, a need for more potent and effective antiepileptic drugs and drugs with fewer adverse effects, particularly CNS effects. Drugs for the treatment of partial seizures are particularly needed. With major advances in our understanding of the basic neuropathology, neuropharmacology and neurophysiology of epilepsy, numerous candidate novel antiepileptic drugs have been developed in recent years. This review comparatively evaluates the pharmacokinetics, efficacy and adverse effects of 12 new antiepileptic drugs namely vigabatrin, lamotrigine, gabapentin, oxcarbazepine, felbamate, tiagabine, eterobarb, zonisamide, remacemide, stiripentol, topiramate and levetiracetam (ucb-L059). Of the 12 drugs, vigabatrin, lamotrigine and gabapentin have recently been marketed in the UK. Five of these new drugs have known mechanisms of action (vigabatrin, lamotrigine, tiagabine, oxcarbazepine and eterobarb), which may provide for a more rational approach to the treatment of epilepsy. Oxcarbazepine, remacemide and eterobarb are prodrugs. Vigabatrin, gabapentin and topiramate are more promising on the basis of their pharmacokinetic characteristics in that they are excreted mainly unchanged in urine and not susceptible to significant pharmacokinetic interactions. In contrast, lamotrigine, felbamate and stiripentol exhibit significant drug interactions. Essentially, all the drugs are effective in partial or secondarily generalised seizures and are effective to varying degrees in other seizure types. Particularly welcome is the possible effectiveness of zonisamide in myoclonus and felbamate in Lennox-Gastaut syndrome. In relation to adverse effects, CNS effects are observed with all drugs, however, gabapentin, remacemide and levetiracetam appear to exhibit least. There is also the possibility of rational duotherapy, using drugs with known mechanisms of action, as an additional therapeutic approach. The efficacy of these 12 antiepileptic drug occurs despite the fact that candidate antiepileptic drugs are evaluated under highly unfavourable conditions, namely as add-on therapy in patients refractory to drug management and with high seizure frequency. Thus, whilst candidate drugs which do become licensed are an advance in that they are effective and/or are associated with less adverse effects than currently available antiepileptic drugs in these patients, it is possible that these drugs may exhibit even more improved risk-benefit ratios when used in normal clinical practice.

Vigabatrin in the treatment of complex partial seizures

We report the effect of vigabatrin on seizure frequency in 13 severely drug-resistant patients with intractable complex partial seizures (CPS) with or without secondary generalization. Patients were followed for a 3-month period before vigabatrin administration to establish a 'baseline'. Six patients became seizure free for 2-3 weeks immediately after starting vigabatrin. In seven patients a transient (4-6 weeks) increase in seizures above baseline occurred, which was attenuated by vigabatrin dose increments. After 3 months, the mean baseline CPS frequency was reduced from 7.75 +/- 1.18 (median 8, range 2.6-16) to 2.77 +/- 0.7 (median 1, range 0-7). At 6 months a > 50% improvement remained in seven patients. After 12 or more months CPS frequency returned to baseline in four patients, improved (by 25-62.5%) in four and deteriorated in three. One patient who was seizure free lost control at 16 months. Other effects were drowsiness (3), weight increase (3), diarrhoea (1), depression (2) and mood elevation (2). Four patients discontinued vigabatrin; one because of severe depression, three owing to lack of efficacy. Three patients have undergone and two are awaiting neurosurgery for their epilepsy. Thus, CPS frequency progressively deteriorated toward baseline in all patients, however, secondary generalizations were abolished in four and reduced in two.

A review of evidence for GABergic predominance/glutamatergic deficit as a common etiological factor in both schizophrenia and affective psychoses: more support for a continuum hypothesis of "functional" psychosis

Virtually all antidepressant and antipsychotic drugs, including clozapine, rimcazole and lithium ion, are proconvulsants, and convulsive therapy, using metrazol, a known GABA-A antagonist, as well as electro-convulsive therapy, can be effective in treating both schizophrenia and affective psychoses. Many antidepressant and antipsychotic drugs, including clozapine, as well as some of their metabolites, reverse the inhibitory effect of GABA on 35S-TBPS binding, a reliable predictor of GABA-A receptor blockade. A review of relevant literature suggests that 1) "functional" psychoses constitute a continuum of disorders ranging from schizophrenia to affective psychoses with overlap of symptoms, heredity and treatments, 2) a weakening of GABergic inhibitory activity, or potentiation of counterbalancing glutamatergic neurotransmission, in the brain, may be involved in the therapeutic activities of both antidepressant and antipsychotic drugs, and 3) schizophrenia and the affective psychoses may be different expressions of the same underlying defect: GABergic preponderance/glutamatergic deficit. Schizophrenia and affective psychoses share the following: 1) several treatments are effective in both, 2) similar modes of inheritance, 3) congruent seasonal birth excesses, 4) enlarged cerebral ventricles and cerebellar vermian atrophy, 5) dexamethasone non-suppression. Both genetic and environmental factors are involved in both schizophrenia and affective psychoses, and several lines of evidence suggest that important environmental factors are neurotropic pathogens that selectively destroy glutamatergic neurons. One group of genes associated with psychoses may increase vulnerability to attack and destruction, by neurotropic pathogens, of excitatory glutamatergic neurons that counterbalance inhibitory GABergic neurons. A second group of genes may encode subunits of overactive GABA-A receptors, while a third group of genes may encode subunits of hypo-active glutamate receptors. Improved antipsychotic drugs may be found among selective blockers of GABA-A receptor subtypes and/or enhancers of glutamatergic neurotransmission. A mechanism similar to kindling, leading to long-lasting reduction of GABergic inhibition in the brain, may be involved in several treatments of psychoses.