Gamma-vinyl GABA (vigabatrin) and mood disturbances

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

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

Vigabatrin

Refractory epilepsies such as infantile spasms (IS) and complex partial seizures (CPS) can have a severe negative impact on the neurological integrity and quality of life of affected patients, in addition to drastically increasing their risk of premature mortality. Early identification of potentially effective pharmacotherapy agents is important. Vigabatrin has been shown to be a generally well tolerated and effective antiepileptic drug (AED) in a wide variety of seizure types affecting both children and adults, particularly those with IS and CPS. A bilateral, concentric constriction of the peripheral visual field characterizes the visual field defect (VFD) associated with vigabatrin, well characterized by numerous studies. This peripheral VFD presents in 30-50% of patients with exposure of several years; however, most of these patients are asymptomatic. In well-controlled studies, the earliest onset in patients with CPS is 11 months and at 5 months in infants, with average onsets being more than 5 years and 1 year, respectively. Patients with a peripheral VFD retain an average 65 degrees of lateral vision (normal, 90 degrees). The fact that many patients never develop the vigabatrin-related peripheral VFD, despite long-term exposure at high doses, may support the hypothesis that the injury is an idiosyncratic adverse drug reaction (as opposed to a strict dose- or duration-dependent toxicity). Effective testing methods are available to aid in the early detection and management of the peripheral VFD. This article discusses issues of importance to clinical decision-making in the use of vigabatrin to assist the physician and patient in assessing the benefits of vigabatrin therapy and understanding the potential risks of the VFD and uncontrolled seizures.

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.

Long-term open multicentre, add-on trial of vigabatrin in adult resistant partial epilepsy. The Canadian Vigabatrin Study Group

Vigabatrin (VGB) has been shown in a number of clinical trials with varying designs to be effective and well-tolerated as both add-on therapy and monotherapy in epilepsy with partial seizures with or without secondary generalization as well as in infantile spasms. The present study is an open, long-term (1 year) extension of a randomized double-blind placebo-controlled multicentre Canadian trial of VGB in resistant partial adult epilepsy. The present study was designed to examine the safety and long-term efficacy of VGB. Completers of the preceding double-blind study had their dose of VGB titrated to 4 g/day over 3 weeks. Patients were evaluated every 2-4 weeks and at week 14 were allowed to continue only if they achieved a 50% seizure reduction compared with pre-VGB baseline. In addition to neurological and physical examinations, safety was assessed by a cognitive psychosocial test battery, visual and somatosensory evoked potentials and MRI scans. Ninety-seven of 100 eligible patients entered the study, 53 of whom completed the 52 weeks. Fifty-eight percent of the patients had a greater than 50% seizure reduction in seizures vs. pre-VGB baseline. Seizure reductions of 56% and 45%, respectively, were seen in the VGB and placebo groups from the preceding study. Fifty-four percent of patients were judged by the investigators to have experienced at least a moderate therapeutic effect. Discontinuations were 29% for lack of efficacy and 12% for adverse effects. There was a mean weight gain of 3.7 +/- 0.2 kg by end of study. Neurologica/psychiatric side effects were the most common reason for withdrawal including three behavioral reactions attributed to the drug which required temporary hospitalization. There were no abnormalities on laboratory or special tests and there was a tendency for improvement on most tests of cognitive function and mood. Vigabatrin, as an add-on agent, is well-tolerated and can be of long-term benefit in a substantial proportion of patients with intractable partial epilepsy.

The effects of vigabatrin on attention, concentration and mood: an investigation in healthy volunteers

Ten healthy volunteers (six males; four females) completed this double-blind, crossover design study of vigabatrin vs placebo. Subjects were tested on four occasions; at the baselines of the placebo and the vigabatrin phase, and two weeks thereafter. At time of testing, the dose of vigabatrin was 2 g daily. Changes in cognition were assessed using the Sternberg, the PASAT, the Stroop, and Critical Fusion Flicker tests. Mood was assessed with the Mood Adjective Check List, the Beck Depression Inventory, and the Irritability, Depression and Anxiety scales. We found one drug, and one placebo, related significant difference on a measure of cognition.

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.

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.