Vigabatrin

Ion Channels in Genetic Epilepsy: From Genes and Mechanisms to Disease-Targeted Therapies

Epilepsy is a common and serious neurologic disease with a strong genetic component. Genetic studies have identified an increasing collection of disease-causing genes. The impact of these genetic discoveries is wide reaching-from precise diagnosis and classification of syndromes to the discovery and validation of new drug targets and the development of disease-targeted therapeutic strategies. About 25% of genes identified in epilepsy encode ion channels. Much of our understanding of disease mechanisms comes from work focused on this class of protein. In this study, we review the genetic, molecular, and physiologic evidence supporting the pathogenic role of a number of different voltage- and ligand-activated ion channels in genetic epilepsy. We also review proposed disease mechanisms for each ion channel and highlight targeted therapeutic strategies.

γ-Aminobutyric acid (GABA) signalling in plants

The role of γ-aminobutyric acid (GABA) as a signal in animals has been documented for over 60 years. In contrast, evidence that GABA is a signal in plants has only emerged in the last 15 years, and it was not until last year that a mechanism by which this could occur was identified-a plant 'GABA receptor' that inhibits anion passage through the aluminium-activated malate transporter family of proteins (ALMTs). ALMTs are multigenic, expressed in different organs and present on different membranes. We propose GABA regulation of ALMT activity could function as a signal that modulates plant growth, development, and stress response. In this review, we compare and contrast the plant 'GABA receptor' with mammalian GABAA receptors in terms of their molecular identity, predicted topology, mode of action, and signalling roles. We also explore the implications of the discovery that GABA modulates anion flux in plants, its role in signal transduction for the regulation of plant physiology, and predict the possibility that there are other GABA interaction sites in the N termini of ALMT proteins through in silico evolutionary coupling analysis; we also explore the potential interactions between GABA and other signalling molecules.

De novo GABRA1 mutations in Ohtahara and West syndromes

OBJECTIVE

GABRA1 mutations have been identified in patients with familial juvenile myoclonic epilepsy, sporadic childhood absence epilepsy, and idiopathic familial generalized epilepsy. In addition, de novo GABRA1 mutations were recently reported in a patient with infantile spasms and four patients with Dravet syndrome. Those reports suggest that GABRA1 mutations are associated with infantile epilepsy including early onset epileptic encephalopathies. In this study, we searched for GABRA1 mutations in patients with infantile epilepsy to investigate the phenotypic spectrum of GABRA1 mutations.

METHODS

In total, 526 and 145 patients with infantile epilepsy were analyzed by whole-exome sequencing and GABRA1-targeted resequencing, respectively.

RESULTS

We identified five de novo missense GABRA1 mutations in six unrelated patients. A p.R112Q mutation in the long extracellular N-terminus was identified in a patient with infantile epilepsy; p.P260L, p.M263T, and p.M263I in transmembrane spanning domain 1 (TM1) were identified in three unrelated patients with West syndrome and a patient with Ohtahara syndrome, respectively; and p.V287L in TM2 was identified in a patient with unclassified early onset epileptic encephalopathy. Four of these mutations have not been observed previously.

SIGNIFICANCE

Our study suggests that de novo GABRA1 mutations can cause early onset epileptic encephalopathies, including Ohtahara syndrome and West syndrome.

Rett Syndrome: Reaching for Clinical Trials

Rett syndrome (RTT) is a syndromic autism spectrum disorder caused by loss-of-function mutations in MECP2. The methyl CpG binding protein 2 binds methylcytosine and 5-hydroxymethycytosine at CpG sites in promoter regions of target genes, controlling their transcription by recruiting co-repressors and co-activators. Several preclinical studies in mouse models have identified rational molecular targets for drug therapies aimed at correcting the underlying neural dysfunction. These targeted therapies are increasingly translating into human clinical trials. In this review, we present an overview of RTT and describe the current state of preclinical studies in methyl CpG binding protein 2-based mouse models, as well as current clinical trials in individuals with RTT.

Targeted pharmacological treatment of autism spectrum disorders: fragile X and Rett syndromes

Autism spectrum disorders (ASDs) are genetically and clinically heterogeneous and lack effective medications to treat their core symptoms. Studies of syndromic ASDs caused by single gene mutations have provided insights into the pathophysiology of autism. Fragile X and Rett syndromes belong to the syndromic ASDs in which preclinical studies have identified rational targets for drug therapies focused on correcting underlying neural dysfunction. These preclinical discoveries are increasingly translating into exciting human clinical trials. Since there are significant molecular and neurobiological overlaps among ASDs, targeted treatments developed for fragile X and Rett syndromes may be helpful for autism of different etiologies. Here, we review the targeted pharmacological treatment of fragile X and Rett syndromes and discuss related issues in both preclinical studies and clinical trials of potential therapies for the diseases.

Treatment of infantile spasms

BACKGROUND

Infantile spasms (West's Syndrome) is a syndrome that includes a peculiar type of epileptic seizure-the spasms-and an electroencephalographic (EEG) abnormality often called hypsarrhythmia. Psychomotor retardation is frequently found at follow-up. Approximately two-thirds of affected infants will have a detectable underlying neurological abnormality, but still little is known about the pathophysiological basis for infantile spasms, and treatment remains problematic.

OBJECTIVES

To compare the effects of single pharmaceutical therapies used to treat infantile spasms in terms of control of the spasms, resolution of the EEG, relapse rates, psychomotor development, subsequent epilepsy, side effects, and mortality.

SEARCH METHODS

To identify published data, we searched the Cochrane Epilepsy Group Specialised Register (October 2012), CENTRAL (The Cochrane Library 2012, Issue 9), MEDLINE (1946 to September Week 4, 2012), EMBASE (1980 to March 2003), and the reference lists of all retrieved articles.To identify unpublished data, we searched the ISRCTN Register (www.controlled-trials.com), corresponded with colleagues and drug companies, and made requests at international conferences.

SELECTION CRITERIA

All randomised controlled trials (RCTs) of the administration of drug therapy to patients with infantile spasms.

DATA COLLECTION AND ANALYSIS

Data collection from all relevant publications was independently undertaken by three review authors (before 2010) or by two review authors using a standard proforma. Analysis included assessment of study quality and a search for sources of heterogeneity.

MAIN RESULTS

We found 16 small RCTs (fewer than 100 patients enrolled) and 2 larger RCTs (more than 100 patients enrolled). These 18 studies looked at a total of 916 patients treated with a total of 12 different pharmaceutical agents. Overall methodology of the studies was poor, in part because of ethical dilemmas such as giving placebo injections to children. Two studies showed that placebo was not as good as active treatment in resolving the spasms. The strongest evidence suggested that hormonal treatment (prednisolone or tetracosactide depot) leads to resolution of spasms faster and in more infants than does vigabatrin. Responses without subsequent relapse may be no different. The same study suggests that hormonal treatments might improve the long-term developmental outcome compared with vigabatrin in infants not found to have an underlying cause for their infantile spasms.

AUTHORS' CONCLUSIONS

To date, few well-designed RCTs have considered the treatment of infantile spasms, and the numbers of patients enrolled have been small. In the majority, methodology has been poor, hence it is not clear which treatment is optimal in the treatment of this epilepsy syndrome. Hormonal treatment resolves spasms in more infants than vigabatrin, but this may or may not translate into better long-term outcomes. If prednisolone or vigabatrin is used, high dosage is recommended. Vigabatrin may be the treatment of choice in tuberous sclerosis. Resolution of the EEG features may be important, but this has not been proven. Further research using large studies with robust methodology is required.

Treatment of infantile spasms

BACKGROUND

Infantile spasms (West's Syndrome) is a syndrome which includes a peculiar type of epileptic seizure, the spasms, and an electroencephalogram (EEG) abnormality often called hypsarrhythmia. Psychomotor retardation is frequently found at follow up. Approximately two thirds of affected infants will have a detectable underlying neurological abnormality, but still little is known about the pathophysiological basis for infantile spasms and treatment remains problematic.

OBJECTIVES

To compare the effects of single pharmaceutical therapies used to treat infantile spasms in terms of control of the spasms, resolution of the EEG, relapse rates, psychomotor development, subsequent epilepsy, side effects, and mortality.

SEARCH STRATEGY

Published data: Cochrane Epilepsy Group Specialised Register, CENTRAL (The Cochrane Library 2007, Issue 4), MEDLINE, EMBASE, and the reference lists of all retrieved articles.Unpublished data: ISRCTN Register (www.controlled-trials.com), correspondence with colleagues and drug companies, and requests at international conferences.

SELECTION CRITERIA

All randomised controlled trials of the administration of drug therapy to patients with infantile spasms.

DATA COLLECTION AND ANALYSIS

Data collection from all relevant publications was independently undertaken by three review authors using a standard proforma. Analysis included assessment of study quality and looking for sources of heterogeneity.

MAIN RESULTS

We found 12 small RCTs (less than 60 patients enrolled) and two larger RCT (more than 100 patients enrolled). These 14 studies looked at a total of 681 patients treated with a total of nine different pharmaceutical agents. Overall methodology of the studies was poor, partly because of ethical dilemmas such as giving placebo injections to children. Two studies showed that placebo was not as good as active treatment in resolving the spasms. The strongest evidence suggested that hormonal treatment leads to resolution of spasms faster and in more infants than does vigabatrin. Responses without subsequent relapse may be no different. The same study suggests that hormonal treatments (prednisolone or tetracosactide) might improve the long-term developmental outcome compared with vigabatrin in infants not found to have an underlying cause for their infantile spasms.

AUTHORS' CONCLUSIONS

To date, there have been few well-designed RCTs that considered the treatment of infantile spasms, and the numbers of patients enrolled have been small. Overall methodology has been poor, hence it is not clear which treatment is optimal in the treatment of this epilepsy syndrome. Hormonal treatment resolves spasms in more infants than vigabatrin but this may or may not translate into a better long-term outcome. If prednisone or vigabatrin are used then high dosage is recommended. Vigabatrin may be the treatment of choice in tuberous sclerosis. Resolution of the EEG features may be important but this has not been proven. Further research using large studies with robust methodology is still required.

Inhibition of basal and stimulated release of endothelin-1 from guinea pig tracheal epithelial cells in culture by beta 2-adrenoceptor agonists and cyclic AMP enhancers

The effects of cyclic AMP-related compounds and beta adrenoceptor agonists on the basal and lipopolysaccharide (LPS)-stimulated release of endothelin-1 (ET-1) from guinea-pig tracheal epithelial cells (GPTEpCs) in culture were studied. Forskolin (a potent activator of adenylyl cyclase), 8-bromo-cyclic AMP (a cyclic AMP analogue), salbutamol and salmeterol (two beta 2-adrenoceptor agonists), were used to increase cyclic AMP levels. Cultured GPTEpCs released ET-1 continuously over a 24 h incubation period. The values reached 1,938 +/- 122 pg/mg of total cell proteins after 24 h. LPS (10 microg/ml) significantly stimulated the release of ET-1 by 1.6- to 1.8-fold, up to 1,262 +/- 56 pg/mg total cell proteins after an 8 h incubation period. Compound 8-bromo-cyclic AMP (10(-5), 10(-4) and 10(-3) M) reduced the basal release of ET-1 from GPTEpCs by up to 31% (P < 0.01) and the LPS stimulated release by up to 42% (P < 0.05), after an 8 h incubation period. Forskolin (10(-6), 10(-5) and 10(-4) M) also inhibited the basal release of ET-1 by up to 28% (P < 0.05) and LPS-stimulated release of ET-1 by up to 50% (P < 0.05), after an 8 h incubation period. At the concentration of 10(-5) M, forskolin increased cyclic AMP levels in GPTEpCs by 17-fold (P < 0.001) in the medium, 15 min after the beginning of the incubation. Salbutamol (10(-8) to 10(-6) M) had no effect on the basal production and release of ET-1 after 8 h. Conversely, this short acting beta 2-adrenoceptor agonist significantly reduced LPS-mediated increase of ET-1 production by up to 55% (P < 0.05) after an 8 h incubation period. Salmeterol (10(-9) M to 10(-5) M) inhibited basal and LPS-stimulated production and release of ET-1 after an 8 h incubation period (between 44 and 51%, P < 0.01). Both salbutamol and salmeterol (10(-6) M) increase cyclic AMP levels by five- and twofold, respectively (P < 0.05). In summary, these observations indicate that beta 2-adrenoceptor agonists or cyclic AMP enhancers can modulate both basal and more markedly, the enhanced production of ET-1 from LPS-activated guinea pig airway EpCs. In addition, these compounds increase cyclic AMP levels in the cells. It is suggested that there is a correlation between cyclic AMP increase and inhibition of ET-1 release by guinea pig airway EpCs. Since ET-1 production was shown to be elevated in asthmatic subjects and in patients suffering from other inflammatory lung disorders, the inhibition of its production by beta adrenoceptor agonists, such as salbutamol and salmeterol, could be added to their therapeutical benefits.

Addition of transdermal or inhaled long-acting Beta2-agonists in adult asthmatic patients treated with inhaled corticosteroids: switchover study from tulobuterol patch to salmeterol dry powder inhaler

Sixty-four patients with persistent asthma receiving 200 to 800 microg of fluticasone propionate daily were enrolled in this switchover study. The patients applied a tulobuterol patch 2 mg every 24 hours for 4 weeks followed by inhalation of salmeterol 100 microg bid for 4 weeks. The mean values for morning and evening peak expiratory flow improved significantly compared with baseline during the 4 weeks of tulobuterol patch treatment. Further improvement was seen on switching to salmeterol treatment, which was significant even in the first week, and continued until the final week of the study. Use of salmeterol alone resulted in a significant increase in the percentage of forced expiratory volume in 1 second %FEV1 from baseline, with 51% of patients feeling that the treatment was effective (vs. 37% on tulobuterol). These data suggest that salmeterol can achieve better control in asthmatic patients after switching from using tulobuterol patches.

Tiagabine does not attenuate alcohol-induced activation of the human reward system

RATIONALE

The rewarding effects of ethanol and other drugs of abuse are mediated by activation of the mesolimbic dopamine system. Recent neuroimaging studies in primates and humans suggest that cocaine-induced dopamine stimulation might be diminished by drugs augmenting gamma-aminobutyric acid A (GABA-A) receptor function such as the GABA transaminase inhibitor vigabatrin.

OBJECTIVES

The objective of this study was to test the property of the selective GABA transporter 1 (GAT1) inhibitor tiagabine to block ethanol-induced activation of the mesolimbic reward system in an i.v. ethanol challenge.

MATERIALS AND METHODS

Twenty nonaddicted healthy volunteers underwent an i.v. ethanol challenge after 1 week of tiagabine (15 mg/day) administration. Neuronal activation was measured using [(18)F]-fluoro-deoxyglucose positron emission tomography (PET).

RESULTS

Tiagabine did not prevent ethanol-induced stimulation of the mesolimbic reward system but augmented ethanol-induced hypometabolism within areas of the visual system and the cerebellum. Tiagabine alone also decreased neuronal metabolism within parts of the right temporal cortex that are highly enriched with GABA-ergic neurons.

CONCLUSIONS

Our ethanol challenge imaging study does not provide supporting evidence that the GAT1 inhibitor tiagabine diminishes the rewarding effects of ethanol. Further PET imaging studies using established anticraving compounds, such as the mu-opioid receptor antagonist naltrexone and antiepileptic drugs affecting the GABA-ergic system more broadly, will provide additional important insights on the interaction between the GABA-ergic and the brain reward system in vivo and the suitability of GABA-ergic drugs as anticraving compounds.

The pharmacokinetics of antiepileptic drugs in rats: consequences for maintaining effective drug levels during prolonged drug administration in rat models of epilepsy

Rodent models of chronic epilepsy with spontaneous recurrent seizures likely represent the closest parallel to the human condition. Such models may be best suited for therapy discovery for pharmacoresistant epilepsy and for antiepileptogenic or disease-modifying therapeutics. However, the use of such rodent models for therapy discovery creates problems with regard to maintaining effective drug levels throughout a prolonged testing period. This is particularly due to the fact that rodents such as rats and mice eliminate most drugs much more rapidly than humans. Thus, knowledge about elimination rate of a test drug in a laboratory species is essential for development of a treatment paradigm that allows maintaining adequate drug levels in the system over the period of treatment. Currently, the most popular models of epilepsy with spontaneous seizures are poststatus epilepticus models of temporal lobe epilepsy in rats. Such models are both used for studies on antiepileptogenesis and drug resistance. For validation of these models, current antiepileptic drugs (AEDs) have to be used. In this article, the elimination rates of these AEDs and their effective plasma levels in rats are reviewed as a guide for developing treatment protocols for chronic drug testing. The advantages and disadvantages of several technologies for drug delivery are discussed, and some examples for calculation of adequate treatment protocols are given. As shown in this review, because of the rapid elimination of most AEDs in rats, it is no trivial task to maintain effective steady-state AED levels in the plasma throughout the day over multiple days to ensure that there will be adequate levels in the system for the purpose of the experiment. However, the use of an adequate dosing regimen that is based on elimination rate is an absolute prerequisite when using rat models for discovery of new antiepileptogenic therapies or therapies for pharmacoresistant epilepsy, because otherwise such models may lead to erroneous conclusions about drug efficacy.

Salmeterol improves pulmonary function in persons with tetraplegia

beta(2)-Adrenergic agonists are known to improve muscle strength because of anabolic properties. The purpose of this study was to determine if long-term administration of a long-acting beta(2)-adrenergic agonist to subjects with tetraplegia is associated with improvement in pulmonary function parameters and maximal static inspiratory and expiratory mouth pressures (MIP and MEP, respectively), measures of respiratory muscle strength. The study was a randomized, prospective, double-blind, placebo-controlled, crossover trial and conducted at the James J. Peters Veterans Affairs Medical Center. Thirteen subjects who had complete or incomplete tetraplegia for more than one year participated in the study. Eleven subjects completed the study. All were clinically stable outpatients without any history of asthma or use of inhaled bronchodilators. Following baseline measurements, patients were randomized to receive salmeterol or placebo from identically marked Diskus containers for 4 weeks. Following a 4-week washout period, the subjects were randomized to receive the alternate preparation for 4 weeks. Pulmonary function parameters and static mouth pressure were measured during baseline and during the fourth week of the two study periods. During the 4-week period of salmeterol administration, forced vital capacity, forced expiratory volume in 1 s, peak expiratory flow, MIP, and MEP improved significantly compared with placebo and baseline. Expiratory reserve volume increased significantly compared to baseline. Increases in MIP and MEP during salmeterol administration suggest improvement in respiratory muscle strength. However, this cannot be stated with certainty because MIP and MEP are dependent on volume parameters at which they are measured. Regardless of the mechanism, improvement in static mouth pressures indicates that salmeterol should benefit these individuals by improving cough effectiveness.

Double-blind, double-dummy, multinational, multicenter, parallel-group design clinical trial of clinical non-inferiority of formoterol 12 microg/unit dose in a b.i.d. regimen administered via an HFA-propellant-pMDI or a dry powder inhaler in a 12-week treatment period of moderate to severe stable persistent asthma in adult patients

BACKGROUND

Pressurized metered-dose inhalers (pMDIs) have traditionally used CFCs as propellants. However, the worldwide phase-out of CFCs has necessitated the development of new pMDIs that use alternative propellants. One such replacement is the hydrofluoroalkane HFA-134a.

OBJECTIVES

This study sought to establish the clinical non-inferiority of a new HFA-134a-containing pMDI to a conventional dry powder inhaler (DPI) in the administration of formoterol to adult patients with moderate-to-severe, stable persistent asthma. The secondary aim was to collect safety data in a multiple-dose long-term study.

METHODS

During this multicenter, double-blind, parallel study, 500 patients were randomized to receive 12 microg of formoterol twice daily for 12 weeks via either an HFA pMDI or a DPI. If necessary, the dose could be increased to 24 microg twice daily. At baseline, all patients (aged 18-70 years) had an FEV1 40-80% of predicted and a documented positive response to the reversibility test.

RESULTS

After 12 weeks' therapy, the adjusted mean morning PEFR was 343.69 l/min in the formoterol HFA pMDI group and 344.56 l/min in the formoterol DPI group. Because the lower limit of the 95% CI for the between-group difference (-11.64 l/min) was well within the non-inferiority margin (-20 l/min), the HFA device was deemed clinically non-inferior to the DPI device. This finding was confirmed when evening PEFR and FEV1 were assessed. Both formulations of formoterol were well tolerated during prolonged multiple dosing.

CONCLUSIONS

This study provides evidence that the new HFA-formulated formoterol pMDI has a similar efficacy and safety profile to the conventional formoterol DPI in the treatment of patients with moderate-to-severe asthma.

Treatment of infantile spasms

BACKGROUND

Infantile spasms (West's Syndrome) is a syndrome which includes a peculiar type of epileptic seizure, usually hypsarrhythmia and in the majority of people, psychomotor retardation. It remains poorly understood and despite modern imaging techniques an underlying cause is often not found. Little is known about their pathophysiological basis and treatment remains problematic.

OBJECTIVES

To compare the effects of single drugs used to treat infantile spasms in terms of long-term psychomotor development, subsequent epilepsy, control of the spasms and adverse effects.

SEARCH STRATEGY

Our search included the Cochrane Epilepsy Group trials register, MEDLINE (1966 to 2003) and EMBASE (1981 to 2003), contacting pharmaceutical companies and appeals at international conferences.

SELECTION CRITERIA

All randomised controlled trials (RCTs) of the administration of drugs to people with infantile spasms.

DATA COLLECTION AND ANALYSIS

Three reviewers independently selected trials for inclusion and extracted data. Outcomes included cessation of spasms, time to cessation of spasms, participants with cessation of spasms remaining spasm free, reduction in spasms, resolution of hypsarrhythmia, subsequent epilepsy rates and adverse effects.

MAIN RESULTS

Eleven RCTs were included, who in total recruited just 514 participants and tested eight different drugs. Overall, methodology of the studies was poor. No study assessed long-term psychomotor development or onset of other seizure types. One small study found vigabatrin to be more efficacious than hydrocortisone in stopping infantile spasms in a group of people with tuberous sclerosis. One underpowered study showed a trend for vigabatrin to be more efficacious than placebo in stopping infantile spasms. Two small studies when combined showed ACTH to be more efficacious than low-dose prednisone (2 mg/kg). One study also suggested that control of spasms occurred more frequently with high dose vigabatrin as compared to low dose vigabatrin. It was not possible to compare reduction in the number of spasms between the different treatments because of differences in methods of analysis. Overall, only 18 individuals were reported to have been withdrawn from the trial treatments due to adverse effects and 4 deaths were reported.

REVIEWER'S CONCLUSIONS

We found no single treatment to be proven to be more efficacious in treating infantile spasms than any of the others (other than vigabatrin in the treatment of infantile spasms in tuberous sclerosis in one underpowered study). Few studies considered psychomotor development or subsequent seizure rates as outcomes and none had long-term follow-up. Further trials with larger numbers of participants, and longer follow-up are required.

The treatment of West syndrome: a Cochrane review of the literature to December 2000

BACKGROUND

West syndrome is an age dependent syndrome, which includes a peculiar type of epileptic seizure (infantile spasms), usually hypsarrhythmia and in the majority psychomotor retardation. Despite huge advances in medicine it still remains a poorly understood entity and although with newer imaging techniques we are more often able to elicit the underlying 'causes' of these spasms, still little is known about their pathophysiological basis and treatment remains problematic.

OBJECTIVES

To compare the effects of single pharmaceutical therapies used to treat infantile spasms in terms of long-term psychomotor development, subsequent epilepsy, control of the spasms and side effects.

METHODS

A search of the central trials register of the Cochrane Epilepsy Group, medline database, embase database and the reference lists of all retrieved articles was undertaken. Correspondence with colleagues and drug companies and appeals at international conferences were also undertaken to try and discover unpublished data. All randomised controlled trials (RCTs) on the medical treatment of infantile spasms were included. Data was then extracted independently by the three reviewers and analysed using the RevMan software package.

MAIN RESULTS

We found ten small RCTs on the pharmacological treatment of infantile spasms. No unpublished trials were discovered. These ten studies looked at just 335 patients treated with a total of eight different pharmaceutical agents. Overall methodology of the studies was poor, partly because of ethical dilemmas such as giving placebo injections to children. No study considered the effects of treatment on long-term psychomotor development or onset of other seizure types. One small study found vigabatrin to be more efficacious in stopping infantile spasms in a group of patients with tuberous sclerosis than hydrocortisone. One underpowered study showed a trend for vigabatrin to be more efficacious than placebo in stopping infantile spasms, another two equally underpowered studies suggested adrenocorticotrophic hormone (ACTH) to be more efficacious than low-dose prednisone. It was not possible to compare reduction in the number of spasms between the different treatments because of differences in methods of analysis. Overall, only nine patients were reported to have been withdrawn from the trial treatments due to side effects and two deaths were reported.

CONCLUSIONS

There is still little evidence available on the optimum treatment for infantile spasms. Further trials with larger number of patients, and longer follow-up are required.

Increased vigabatrin entry into the brain by polysorbate 80 and sodium caprate

The effects of a non-ionic surfactant, polysorbate 80, and the sodium salt of the saturated fatty acid, sodium caprate (C10), as potential brain absorption enhancers for vigabatrin were studied. Vigabatrin is an enzyme-activated irreversible inhibitor of gamma-aminobutyric acid (GABA) transaminase that increases brain and cerebrospinal GABA concentrations in animals and man. Before intravenous administration, a range of concentrations of the surfactants were tested using erythrocyte lysis or the red blood cell lysis test to establish the non-toxic concentration range. Vigabatrin was dissolved in 0.1% polysorbate 80 and 0.1% sodium caprate and administered intravenously in doses of 4 mL kg(-1) to male Wistar rats (230-250 g; n = 3). Rats were killed 2 h after drug and surfactant administration and the brains were immediately removed and homogenized in 0.4 M perchloric acid. Selected ion monitoring electrospray mass spectrometry was used to determine the concentration of vigabatrin and GABA directly from the perchloric acid extract of the rat brain. This method was developed to increase the speed and efficiency of the analysis by removing the need for complex extraction and derivatization procedures while retaining the specificity of the mass spectrometer as a detector. The stability of both vigabatrin and GABA in perchloric acid was established by monitoring their pseudo molecular ions in standard solutions at timed intervals over 24 h. Although the detection level for vigabatrin and GABA was at least 50 pg, only GABA was detected in rat brain. Vigabatrin caused a small increase in whole brain GABA. However, GABA levels were higher in the samples with vigabatrin + enhancer than in the samples where vigabatrin alone was administered. One-way analysis of variance indicated a significant effect of the surfactants on GABA levels (F (5,17) = 11.86, P < 0.01) and vigabatrin absorption was presumed. The rectal temperature of the rats is lowered by the presence of vigabatrin in the brain. Vigabatrin alone decreased rectal temperature by 6%. When given with either polysorbate 80 or sodium caprate, the extent of temperature lowering was significantly greater (P < 0.001). There was no significant difference after 2 h between polysorbate 80 + vigabatrin, and sodium caprate + vigabatrin.

Lack of subsensitivity to albuterol after treatment with salmeterol in patients with asthma

The development of tolerance to the bronchodilator effects of beta2-agonists used in asthma therapy has been the subject of debate. We conducted two placebo-controlled crossover studies to assess the bronchodilator response to a short-acting beta2-agonist before and after chronic therapy with salmeterol. Patients in one study were corticosteroid-naive; patients in the other study were using inhaled corticosteroids. Changes in FEV1 after cumulative doubling doses of inhaled albuterol were assessed after a 2-wk beta-agonist washout period, before administering study medication on Day 1, and again after 28 d of therapy. Ipratropium bromide was provided as rapid-relief treatment for asthma, and use of any beta2-agonist except the study treatment was prohibited. On both assessment days for salmeterol, and during placebo administration periods, significant increases from predose FEV1 values were observed beginning with the lowest dose of albuterol and continuing throughout the dose-response assessment (p </= 0.001). These increases in FEV1 were maintained for 6 h after the last dose of albuterol (p < 0.05). There were no statistically significant differences in the albuterol dose response following salmeterol or placebo. These studies indicate that irrespective of concurrent corticosteroid treatment, chronic therapy with salmeterol does not result in tolerance to the bronchodilator effects of albuterol.

Acute bronchodilatory effect of salmeterol on methacholine-induced bronchoconstriction in childhood asthma

A review of the literature highlights the need for research, particularly on the acute bronchodilatory effect of salmeterol on bronchoconstriction in the pediatric age group. The present study attempted to evaluate the acute bronchodilatory effect of salmeterol on methacholine-induced bronchoconstriction in childhood asthma and to compare it with the effect of salbutamol. Forty-four asymptomatic children with mild-to-moderate asthma (23 boys and 21 girls; aged 7-17 years) were studied. At the beginning, the baseline forced expiratory volume in 1 s (FEV1) was measured, and the methacholine challenge was performed by doubling the dose to determine PC20 (provocative concentration of inhaled methacholine required to reduce FEV1 by 20%). At the same time, the transcutaneous arterial oxygen saturation (SaO2) was also measured. Each subject inhaled a single dose of 25 micrograms salmeterol (n: 23, group I) or 100 micrograms salbutamol (n: 21, group II) following the SaO2 measurement. The same measurements (FEV1, SaO2) were repeated 5 and 20 min after the inhalation. After inhalation of salmeterol or salbutamol, the differences between the values of FEV1 and SaO2 after 5 and 20 min were insignificant in both group I and group II (P > 0.05), although there was a significant improvement in both FEV1 and SaO2 after 5 and 20 min (P < 0.005). From these findings it was concluded that salmeterol can be considered as effective as salbutamol on methacholine-induced bronchoconstriction.

Plasma concentrations of vigabatrin in epileptic patients

OBJECTIVE

To measure plasma concentrations of vigabatrin in a group of 30 adult epileptic patients with complex partial seizures (CPS) refractory to conventional antiepileptic drugs. With a view to better defining the drug's dose-response relationships in the presence of concomitant alternative antiepileptic drugs.

METHODS

High-performance liquid chromatographic analysis of blood samples drawn at steady-state trough levels from patients receiving vigabatrin.

RESULTS

The steady-state plasma concentrations of vigabatrin showed marked interpatient variability (CV = 59.5%). The mean concentration was 42 +/- 25 micrograms/ml (range 11.5-102.7 micrograms/ml). Nineteen patients (63%) had plasma levels between 20 and 60 micrograms/ml. The plasma clearance of vigabatrin ranged from 0.24 to 1.37 ml/min/kg (mean +/- SD = 0.74 +/- 0.40 ml/min/kg), with a median value of 0.64 ml/min/kg. Concomitant treatment with carbamazepine increased the plasma clearance of vigabatrin from 0.59 ml/min/kg (monotherapy), 0.54 ml/min/kg (co-treated with phenobarbital) and 0.41 ml/min/kg (co-treated with valproic acid) to 0.92 ml/min/kg.

CONCLUSION

Vigabatrin plasma levels show wide interpatient variability, and co-administration with carbamazepine increases vigabatrin's clearance. While there is no relationship between plasma level and anti-epileptic effect, abnormally high levels of the drug may increase toxicity.

Anticonvulsant Therapy in Children: An Update

Over the years, extensive research has led to the development of a new generation of anticonvulsant medications for the treatment of patients with intractable seizure disorders. Currently three new drugs have been approved in the United States since 1993, and many others have entered into the later stages of development. The purpose of this article is to discuss the pharmacology, pharmacokinetics, drug interactions, clinical use, adverse effects, and dosage and administration of felbamate, gabapentin, lamotrigine, and vigabatrin. Felbamate is indicated in children as adjunctive therapy in the treatment of partial and generalized seizures secondary to Lennox-Gastaut syndrome. Because of life-threatening adverse effects, including aplastic anemia and hepatotoxicity, felbamate is reserved for use only when the benefits of treatment outweigh the risks of toxicity. Presently, gabapentin is indicated as adjunctive treatment of partial seizures with or without generalization in patients older than 12 years of age. To date gabapentin has not been studied in patients younger than age 12 years. Even though lamotrigine is not approved by the Food and Drug Administration (FDA) for pediatric use, preliminary clinical trials show promising results in the treatment of partial and absence seizures as well as Lennox-Gastaut syndrome. Many studies have evaluated the use of vigabatrin for the treatment of intractable seizures. Seizure types most effectively treated include partial seizures, Lennox-Gastaut syndrome, and possibly infantile spasms. Lamotrigine and vigabatrin should be used with caution in patients with myoclonic seizures because an increase in seizure frequency may occur. Copyright © 1996 by W.B. Saunders Company

Vigabatrin-associated reversible acute psychosis in a child

OBJECTIVE

To describe a child with vigabatrin-associated reversible acute psychosis and review the literature reports on this adverse effect.

CASE SUMMARY

A 7-year-old boy with intractable epilepsy developed acute psychosis 3 days after initiating a rapid vigabatrin dosage escalation. All symptoms resolved within 48 hours after vigabatrin therapy was withdrawn. Two months later, reinitiation of vigabatrin therapy using a slower dosage escalation was well-tolerated by the patient, and he currently is being treated with vigabatrin successfully.

DISCUSSION

Although vigabatrin-associated psychosis is rare, a few cases have been reported in predisposed adult patients, especially in the early stages of treatment. The mechanism of this reaction remains unclear and its incidence is unknown. To our knowledge, there has been no previous report of this adverse effect in children.

CONCLUSIONS

Caution must be taken in children with predisposing factors at the beginning of vigabatrin therapy.

Adjunctive therapy in epilepsy: a cost-effectiveness comparison of alternative treatment options

A pharmaco-economic study of the administration of adjunctive therapy in patients with chronic epilepsy is described. A decision-analytic model has been used, which represents the consequences of treatment over a 1-year time period, when one of three drugs is used first. The cost-effectiveness ratio for clobazam, lamotrigine and vigabatrin have been calculated. The expected cost per patient of treatment over the 1-year period was up to 50% higher with vigabatrin and lamotrigine compared with clobazam, with a cost-effectiveness ratio around 40% higher.

Advances in pharmacotherapy: recent developments in the treatment of epilepsy

Epilepsy is a disorder of the central nervous system in which the clinical symptoms are recurrent seizures. An increased understanding of the underlying mechanism of seizures and more definitive diagnostic procedures have improved the care of the patient with epilepsy. An improved classification of various seizure types, including specific epilepsy syndromes has helped optimize use of the standard antiepileptic drugs. Research on the mechanism of seizures has led to new antiepileptic drugs. More definitive diagnostic procedures have led to more accurate identification of patients likely to benefit from epilepsy surgery. This review focuses on these areas.