Optimizing the indication of vigabatrin in children with refractory epilepsy

Pharmacokinetics and tissue distribution of vigabatrin enantiomers in rats

Purpose

To investigate the pharmacokinetics and tissue distribution of VGB racemate and its single enantiomers, and explore the potential of clinic development for single enantiomer S-VGB.

Methods

In the pharmacokinetics study, male Sprague-Dawley rats were gavaged with VGB racemate or its single enantiomers dosing 50, 100 or 200 mg/kg, and the blood samples were collected during 12 h at regular intervals. In the experiment of tissue distribution, VGB and its single enantiomers were administered intravenously dosing 200 mg/kg, and the tissues including heart, liver, spleen, lung and kidney, eyes, hippocampus, and prefrontal cortex were separated at different times. The concentrations of R-VGB and S-VGB in the plasma and tissues were measured using HPLC.

Results

Both S-VGB and R-VGB could be detected in the plasma of rats administered with VGB racemate, reaching Cmax at approximately 0.5 h with t1/2 2-3 h. There was no significant pharmacokinetic difference between the two enantiomers when VGB racemate was given 200 mg/kg and 100 mg/kg. However, when given at the dose of 50 mg/kg, S-VGB presented a shorter t1/2 and a higher Cl/F than R-VGB, indicating a faster metabolism of S-VGB. Furthermore, when single enantiomer was administered respectively, S-VGB presented a slower metabolism than R-VGB, as indicated by a longer t1/2 and MRT but a lower Cmax. Moreover, compared with the VGB racemate, the single enantiomers S-VGB and R-VGB had shorter t1/2 and MRT, higher Cmax and AUC/D, and lower Vz/F and Cl/F, indicating the stronger oral absorption and faster metabolism of single enantiomer. In addition, regardless of VGB racemate administration or single enantiomer administration, S-VGB and R-VGB had similar characteristics in tissue distribution, and the content of S-VGB in hippocampus, prefrontal cortex and liver was much higher than that of R-VGB.

Conclusions

Although there is no transformation between S-VGB and R-VGB in vivo, those two enantiomers display certain disparities in the pharmacokinetics and tissue distribution, and interact with each other. These findings might be a possible interpretation for the pharmacological and toxic effects of VGB and a potential direction for the development and optimization of the single enantiomer S-VGB.

Stiripentol and vigabatrin current roles in the treatment of epilepsy

INTRODUCTION

Stiripentol and vigabatrin are the two anticonvulsant drugs currently approved in severe infantile-onset epilepsies, respectively Dravet syndrome and infantile spasms.

AREAS COVERED

For both, the indication was discovered by chance thanks to an exploratory study. Both demonstrated indisputable efficacy through randomized-controlled trials. Stiripentol as adjunctive therapy to clobazam and valproate performed better than placebo, and vigabatrin as first-line monotherapy better than the reference steroid therapy in spasms due to tuberous sclerosis. At one-year treatment vigabatrin and steroids were equally efficient in the other etiologies of spasms. However, it took more than 20 years for both drugs to be approved world-wide.

EXPERT OPINION

Stiripentol suffered from pharmacokinetic potentiation of clobazam, thus raising the question whether it was efficient per se. Finally, animal models and pharmacogenetic data on CYP2C19 confirmed its specific anticonvulsant effect. Stiripentol (in comedication with clobazam and valproate) is therefore to be recommended for Dravet patients. Vigabatrin was found to have a frequent and irreversible retinal toxicity, which required an alternative visual testing to be detected in young children. Today the benefit/risk ratio of vigabatrin as first-line is considered to be positive in infantile spasms, given the severity of this epilepsy and the lack of a safer alternative therapy.

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.

Neurogenetic disorders and treatment of associated seizures

Seizures are a frequent complication associated with several neurogenetic disorders. Antiepileptic medications remain the mainstay of treatment in these patients. We summarized the available data associated with various antiepileptic therapies used to treat patients with neurogenetic disorders who experienced recurrent seizures. A MEDLINE search was conducted to identify articles and abstracts describing the use of antiepileptic therapy for the treatment of various neurogenetic syndromes. Of all the neurogenetic syndromes, only autism spectrum disorders, Angelman syndrome, Rett syndrome, Dravet syndrome, and tuberous sclerosis complex were identified as having sufficient published information to evaluate therapy. Some efficacy trends were identified, including frequent successes with valproic acid with clonazepam for epilepsy with Angelman syndrome; valproic acid, stiripentol, and clobazam (triple combination therapy) for epilepsy with Dravet syndrome; and vigabatrin for infantile spasms associated with tuberous sclerosis complex. Due to a paucity of information regarding the mechanisms by which seizures are generated in the various disorders, approach to seizure control is primarily based on clinical experience and a limited amount of study data exploring patient outcomes. Although exposure of the developing brain to antiepileptic medications is of some concern, the control of epileptic activity is an important undertaking in these individuals, as the severity of eventual developmental delay often appears to correlate with the severity of seizures. As such, early aggressive therapy is warranted.

Stiripentol : in severe myoclonic epilepsy of infancy (dravet syndrome)

Stiripentol is an anticonvulsant used as adjunctive therapy with valproate and clobazam in the management of patients with severe myoclonic epilepsy of infancy (SMEI; Dravet syndrome), a rare form of epilepsy that develops in the first year of life and is subsequently associated with significant morbidity and mortality. Results of a randomized, double-blind trial, in which patients (≥3 years of age) whose SMEI was inadequately controlled with valproate and clobazam received adjunctive therapy with stiripentol or placebo for 2 months, showed a significantly higher response rate in the stiripentol group compared with the placebo group (71 % vs. 5 %; p < 0.0001; primary endpoint). Responders were defined as those patients who experienced a ≥50 % reduction in clonic or tonic-clonic seizure frequency during the second month of the double-blind period compared with baseline. Almost half of the stiripentol recipients were seizure free during this period compared with none in the placebo group. Stiripentol was also statistically superior to placebo for secondary efficacy outcomes in the randomized controlled trial, which included the median number of seizures during the second month of the double-blind period and the mean percentage change from baseline in seizure frequency. These results are supported by efficacy data from other studies in patients with SMEI treated with stiripentol as adjunctive therapy, including a long-term retrospective analysis, prospectively conducted open-label studies and a meta-analysis. Drowsiness, loss of appetite and weight loss are the most frequently reported adverse events with stiripentol, and the drug inhibits various cytochrome P450 isoenzymes, potentially leading to clinically significant drug interactions. Stiripentol is an important addition to the limited treatment options available for the management of patients with SMEI.

The safety and tolerability of newer antiepileptic drugs in children and adolescents

The newer antiepileptic drugs (AEDs) provide more therapeutic options and overall improved safety and tolerability for patients. To provide the best care, physicians must be familiar with the latest tolerability and safety data. This is particularly true in children, given there are relatively fewer studies examining the effects of AEDs in children compared with adults. Since we now have significant paediatric literature on each of these agents, we provide a comprehensive and current literature review of the newer AEDs, focusing on safety and tolerability data in children and adolescents. Because the safety profiles in children differ from those in adults, familiarity with this literature is important for child neurologists and other paediatric caregivers. We have organized the data by organ system for each AED for easier reference.

Visual field loss in patients with refractory partial epilepsy treated with vigabatrin: final results from an open-label, observational, multicentre study

BACKGROUND

Use of the antiepileptic drug vigabatrin is associated with an elevated risk of visual field loss.

OBJECTIVE

To determine the frequency of, and risk factors for, vigabatrin-attributed visual field loss (VAVFL) in the setting of a large-scale, multinational, prospective, observational study.

STUDY DESIGN

A comparative, open-label, parallel-group, multicentre study.

SETTING

Hospital outpatient clinics at 46 centres in five countries.

PATIENTS

734 patients with refractory partial epilepsy, divided into three groups and stratified by age (8-12 years; >12 years) and exposure to vigabatrin. Group I comprised patients treated with vigabatrin for > or =6 months. Group II comprised patients previously treated with vigabatrin for > or =6 months who had withdrawn from the drug for > or =6 months. Group III comprised patients never treated with vigabatrin. Patients underwent perimetry at either 4- or 6-month intervals, for up to 36 months. Visual field outcome was evaluated masked to drug exposure.

INTERVENTION

Perimetry.

MAIN OUTCOME MEASURE

The visual field outcome at each of four analysis points: (i) at enrolment (i.e. baseline, all patients); (ii) for patients exhibiting a conclusive outcome at the initial visual field examination; (iii) for patients exhibiting at least one conclusive outcome to the visual field examinations; and (iv) at the last conclusive outcome to the visual field examinations.

RESULTS

Of the 734 patients, 524 yielded one or more conclusive visual field examinations. For Group I, the frequency of VAVFL at the last conclusive examination was 10/38 (26.3%) for those aged 8-12 years and 65/150 (43.3%) for those aged >12 years. For Group II, the respective frequencies were 7/47 (14.9%) and 37/151 (24.5%). One case resembling VAVFL was present amongst the 186 patients in Group III at the last conclusive examination. The frequency of VAVFL in Groups I and II combined was 20.0% for those aged 8-12 years and 33.9% for those aged >12 years. VAVFL was associated with duration of vigabatrin therapy (odds ratio [OR] up to 15.2; 95% CI 4.4, 51.7), mean daily dose of vigabatrin (OR up to 26.4; 95% CI 2.4, 291.7) and male gender (OR 2.51; 95% CI 1.5, 4.1). VAVFL was more frequently detected with static than with kinetic perimetry (OR up to 0.43; 95% CI 0.24, 0.75).

CONCLUSIONS

Since the probability of VAVFL is positively associated with treatment duration, careful assessment of the risk-benefit ratio of continuing treatment with vigabatrin is recommended in patients currently receiving this drug. All patients continuing to receive vigabatrin should undergo visual field examination at least every 6 months for the duration of treatment. We recommend two-level (three-zone), gradient-adapted, suprathreshold static perimetry of the peripheral field together with threshold perimetry of the central field out to 30 degrees from fixation. The frequency of ophthalmological and perimetric examinations should be increased in the presence of VAVFL.

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.

Treatment of epilepsy: the GABA-transaminase inhibitor, vigabatrin, induces neuronal plasticity in the mouse retina

Vigabatrin was a major drug in the treatment of epilepsy until the discovery that it was associated with an irreversible constriction of the visual field. Nevertheless, the drug is still prescribed for infantile spasms and refractory epilepsy. Disorganization of the photoreceptor nuclear layer and cone photoreceptor damage have been described in albino rats. To investigate the vigabatrin-elicited retinal toxicity further, we examined the retinal tissue of albino mice treated with two vigabatrin doses. The higher dose did not always cause the photoreceptor layer disorganization after 1 month of treatment. However, it triggered a massive synaptic plasticity in retinal areas showing a normal layering of the retina. This plasticity was shown by the withdrawal of rod but not cone photoreceptor terminals from the outer plexiform layers towards their cell bodies. Furthermore, both rod bipolar cells and horizontal cells exhibited dendritic sprouting into the photoreceptor nuclear layer. Withdrawing rod photoreceptors appeared to form ectopic contacts with growing postsynaptic dendrites. Indeed, contacts between rods and bipolar cells, and between bipolar cells and horizontal cells were observed deep inside the outer nuclear layer. This neuronal plasticity is highly suggestive of an impaired glutamate release by photoreceptors because similar observations have been reported in different genetically modified mice with deficient synaptic transmission. Such a synaptic deficit is consistent with the decrease in glutamate concentration induced by vigabatrin. This description of the neuronal plasticity associated with vigabatrin provides new insights into its retinal toxicity in epileptic patients.

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.

Prophylactic antiepileptic treatment in Sturge-Weber disease

PURPOSE

In Sturge-Weber disease, motor and cognitive defects are supposed to result mostly from severe epilepsy. They might, therefore be partly prevented by prophylactic antiepileptic drug treatment. This condition constitutes a possible model for the study of prophylactic drug treatment in severe epilepsy. In the present study, we compared the outcome of patients treated prospectively with phenobarbitone before the first seizure, with those referred following the first seizure, in order to identify the issues related to the evaluation of prophylactic treatment of severe epilepsy.

METHODS

Motor and cognitive outcome were compared in patients treated prophylactically with phenobarbitone (16 cases) and in those treated following the first seizures (21 cases).

RESULTS

Whereas the incidence of motor deficit was similar in both groups (44 vs. 52%), that of mental retardation was lower in the group treated prophylactically (76.2 vs. 43.7%, P< 0.05). The major methodological issues encountered included the small number of patients identified at birth that could be included in the study, the need for randomization taking into account the size of the angioma, and the choice of the prophylactic medication, including the occurrence of epilepsy together with the course of motor and cognitive functions among the endpoints.

CONCLUSION

Prophylactic anti-epileptic drug treatment is worth considering for Sturge-Weber disease, but a randomized prospective study is necessary to determine this. It should be multicentric, take in account the size of the angioma, and decide what the most appropriate medication should be.

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.

Stiripentol in severe myoclonic epilepsy in infancy: a randomised placebo-controlled syndrome-dedicated trial. STICLO study group

BACKGROUND

Stiripentol is an inhibitor of cytochrome P450 that showed antiepileptic efficacy in severe myoclonic epilepsy in infancy (SMEI) in association with clobazam and valproate in an open study. To confirm these results, 41 children with SMEI were included in a randomised, placebo-controlled, add-on trial.

METHODS

After a baseline period of 1 month, placebo (n=20) or stiripentol (n=21) was added to valproate and clobazam during a double-blind period of 2 months. Patients then received stiripentol in an open fashion. Responders were defined as having more than 50% reduction in the frequency of clonic (or tonic-clonic) seizures during the second month of the double-blind period compared with baseline.

FINDINGS

15 (71%) patients were responders on stiripentol (including nine free of clonic or tonic-clonic seizures), whereas there was only one (5%) on placebo (none were seizure free; stiripentol 95% CI 52.1-90.7 vs placebo 0-14.6). The 95% CI of the difference was 42.2-85.7. Percentage of change from baseline was higher on stiripentol (-69%) than on placebo (+7%), p<0.0001. 21 patients on stiripentol had moderate side-effects (drowsiness, loss of appetite) compared with eight on placebo, but side-effects disappeared when the dose of comedication was decreased in 12 of the 21 cases.

INTERPRETATION

This controlled trial shows the antiepileptic efficacy, of add-on stiripentol in children with SMEI. The results also provide good reason to focus studies on a specific epilepsy syndrome-a small sample of patients is sufficient to show the efficacy that might have been missed in a heterogeneous population.

Vigabatrin: a novel therapy for seizure disorders

OBJECTIVE

To review the pharmacology, pharmacokinetics, efficacy, and adverse effects of vigabatrin and its role in the management of seizure disorders.

METHODS

A MEDLINE search of English-language literature from January 1993 through January 1999 was conducted using vigabatrin as a search term to identify pertinent studies and review articles. Additional studies were identified from the bibliographies of reviewed literature. The manufacturer provided postmarketing surveillance data. Priority was given to randomized, double-blind, placebo-controlled studies.

FINDINGS

Vigabatrin is a selective and irreversible inhibitor of gamma-aminobutyric acid transaminase. In controlled clinical trials of vigabatrin add-on therapy in patients with uncontrolled partial seizures, 24-67% of patients achieved a < or =50% reduction in seizure frequency. Data from two comparative trials with carbamazepine monotherapy indicate that vigabatrin monotherapy reduces the frequency of partial seizures in patients with newly diagnosed epilepsy. Vigabatrin also controls infantile spasms, particularly those associated with tuberous sclerosis. Vigabatrin is more effective in patients with partial seizures than in those with generalized seizures. The drug is generally well tolerated. Headache and drowsiness were the most common adverse effects observed in controlled clinical trials; visual field defects, psychiatric reactions, and hyperactivity also have been reported. There are no known clinically significant drug interactions.

CONCLUSIONS

Vigabatrin improves seizure control as add-on therapy for refractory partial seizures and may produce therapeutic benefits in the treatment of infantile spasms. Vigabatrin is generally well tolerated, with a convenient administration schedule, a lack of known significant drug interactions, and no need for routine monitoring of plasma concentrations.

Efficacy of lamotrigine and vigabatrin in drug-resistant epilepsies of childhood

It was the purpose of this study to compare the efficacy and side effects of lamotrigine (LTG) and vigabatrin (VGB) as add-on therapy in epilepsies of childhood resistant to conventional drugs. Retrospective analysis of the medical charts and electroencephalograms of 134 children (LTG 57, VGB 77) was performed considering the various epileptic seizures and syndromes. In general, LTG and VGB had similar efficacy, with 30-40 % of patients demonstrating significant improvement. Few differences according to seizure type and epileptic syndrome were observed. Primary generalized tonic-clonic seizures more frequently improved and less frequently worsened with LTG than with VGB. In tonic seizures the treatment results were significantly more favorable with VGB. Only insignificantly better results occurred with LTG in the generalized group and with VGB in the localization-related group. VGB was significantly more effective in symptomatic than in idiopathic and cryptogenic syndromes. The frequency of adverse reactions with both drugs was close to 60%. However, treatment had to be discontinued because of severe rashes in only a few patients taking LTG or because of behavior disturbances in patients taking VGB.

Stiripentol: efficacy and tolerability in children with epilepsy

PURPOSE

Stiripentol (STP) is a new antiepileptic drug (AED) that inhibits cytochrome P450, resulting in increased plasma concentrations of concomitant AEDs. The efficacy and tolerability of STP as an add-on therapy in children were assessed.

METHODS

Two hundred twelve patients with refractory epilepsy, aged from 1 month to 20.5 years, received STP either in a single-blind, placebo-controlled trial (108 patients) or in a further open trial (104 other patients selected by epilepsy syndrome for possible efficacy based on the results of the previous trial).

RESULTS

Among the 97 patients who could be analyzed for efficacy in the placebo-controlled study, the median seizure frequency was lower at 3 months with STP than with the placebo (p<0.0001); 49% responded to the drug, including 10% who became seizure free. Patients with partial epilepsy had the highest response rate (57%). Results were confirmed in the open study where 68% of the 91 patients receiving STP responded at 3 months. These patients were mainly those with partial epilepsy (73%) who were receiving carbamazepine (CBZ) (75%) as comedication (p<0.001). Ten of the 20 children with severe myoclonic epilepsy in infancy also responded with clobazam (CLB) as comedication. Efficacy was sustained long term in 74% of the 94 patients still receiving STP at a mean 30-month follow-up. Adverse events were reported in 48% of the 212 patients, mainly anorexia and loss of weight, but these events required STP discontinuation in only nine cases. Side effects were minimized in the open trial by optimizing the dose of comedication.

CONCLUSIONS

STP seems to be a promising add-on drug, particularly when combined with CBZ in patients with partial childhood epilepsy refractory to vigabatrin (VGB) and with CLB in patients with severe myoclonic epilepsy in infancy.

Effects of blocking GABA degradation on corticotropin-releasing hormone gene expression in selected brain regions

PURPOSE

The gamma-aminobutyric acid (GABA) degradation blocker gamma-vinyl-GABA (VGB) is used clinically to treat seizures in both adult and immature individuals. The mechanism by which VGB controls developmental seizures is not fully understood. Specifically, whether the anticonvulsant properties of VGB arise only from its elevation of brain GABA levels and the resulting activation of GABA receptors, or also from associated mechanisms, remains unresolved. Corticotropin-releasing hormone (CRH), a neuropeptide present in many brain regions involved in developmental seizures, is a known convulsant in the immature brain and has been implicated in some developmental seizures. In certain brain regions, it has been suggested that CRH synthesis and release may be regulated by GABA. Therefore we tested the hypothesis that VGB decreases CRH gene expression in the immature rat brain, consistent with the notion that VGB may decrease seizures also by reducing the levels of the convulsant molecule, CRH.

METHODS

VGB was administered to immature, 9-day-old rats in clinically relevant doses, whereas littermate controls received vehicle.

RESULTS

In situ hybridization histochemistry demonstrated a downregulation of CRH mRNA levels in the hypothalamic paraventricular nucleus but not in other limbic regions of VGB-treated pups compared with controls. In addition, VGB-treated pups had increased CRH peptide levels in the anterior hypothalamus, as shown by radioimmunoassay.

CONCLUSIONS

These findings are consistent with a reduction of both CRH gene expression and secretion in the hypothalamus, but do not support an indirect anticonvulsant mechanism of VGB via downregulation of CRH levels in limbic structures. However, the data support a region-specific regulation of CRH gene expression by GABA.

Treatment of infantile spasms: results of a population-based study with vigabatrin as the first drug for spasms

PURPOSE

The efficacy of a protocol consisting of vigabatrin (VGB) as the first and adrenocorticotropic hormone (ACTH) or valproate (VPA) as the second drug was studied in the treatment of newly diagnosed infantile spasms (IS) during 1994 to 1997 in a population-based design.

METHODS

Only total disappearance of the spasms with a minimal duration of 1 month was accepted as a response. The treatment response was confirmed by video-EEG study. All infants were studied by magnetic resonance imaging (MRI) or computed tomography (CT) for etiology.

RESULTS

Altogether 42 infants, 10 with cryptogenic and 32 with symptomatic etiology, were treated. Eleven (26%) responded to VGB, five (50%) with cryptogenic, and six (19%) with symptomatic etiology; 91% of infants responded to a dose of 50-100 mg/kg/day, and 82% of them within 1 week. ACTH was offered in combination with VGB to 22 and VPA to four infants for whom VGB failed. Eleven responded to ACTH and one to VPA. In total, 26 (62%) infants responded to the treatment protocol; all (100%) with cryptogenic etiology and 16 (50%) with symptomatic etiology. ACTH treatment was associated with more severe side effects than VGB or VPA. Only one infant relapsed after a spasm-free period with VGB of >4 months, but none after ACTH was combined with VGB.

CONCLUSIONS

We suggest VGB as a first drug to all infants with IS. After a treatment trial of 10-14 days with increasing dose from 50 to 150 mg/kg, ACTH should be considered.

Adverse effects of vigabatrin in Angelman syndrome

New antiepileptic drugs designed for enhancing GABAergic inhibition, such as vigabatrin (VGB) may be effective in Angelman syndrome (AS), because associated convulsions could be related to a reduced GABA-receptor density or receptor abnormality. From our preliminary experiences in four children with AS treated with VGB, we conclude that it may induce and increase seizures in patients with AS.