A lack of clinically apparent vision loss among patients treated with vigabatrin with infantile spasms: The UCLA experience

Epileptic spasms relapse is associated with response latency but not conventional attributes of post-treatment EEG

OBJECTIVE

Relapse of epileptic spasms after initial treatment of infantile epileptic spasms syndrome (IESS) is common. However, past studies of small cohorts have inconsistently linked relapse risk to etiology, treatment modality, and EEG features upon response. Using a large single-center IESS cohort, we set out to quantify the risk of epileptic spasms relapse and identify specific risk factors.

METHODS

We identified all children with epileptic spasms at our center using a clinical EEG database. Using the electronic medical record, we confirmed IESS syndrome classification and ascertained treatment, response, time to relapse, etiology, EEG features, and other demographic factors. Relapse-free survival analysis was carried out using Cox proportional hazards regression.

RESULTS

Among 599 children with IESS, 197 specifically responded to hormonal therapy and/or vigabatrin (as opposed to surgery or other second-line treatments). In this study, 41 (21%) subjects exhibited relapse of epileptic spasms within 12 months of response. Longer duration of IESS prior to response (>3 months) was strongly associated with shorter latency to relapse (hazard ratio = 3.11; 95% CI 1.59-6.10; p = 0.001). Relapse was not associated with etiology, developmental status, or any post-treatment EEG feature.

SIGNIFICANCE

This study suggests that long duration of IESS before response is the single largest clinical predictor of relapse risk, and therefore underscores the importance of prompt and successful initial treatment. Further study is needed to evaluate candidate biomarkers of epileptic spasms relapse and identify treatments to mitigate this risk.

PLAIN LANGUAGE SUMMARY

Relapse of infantile spasms is common after initially successful treatment. With study of a large group of children with infantile spasms, we determined that relapse is linked to long duration of infantile spasms. In contrast, relapse was not associated with the cause of infantile spasms, developmental measures, or EEG features at the time of initial response. Further study is needed to identify tools to predict impending relapse of infantile spasms.

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.

Rapid determination of plasma vigabatrin by LC-ESI-MS/MS supporting therapeutic drug monitoring in children with infantile spasms

Vigabatrin is one of the second-generation anti-seizure medications (ASMs) designated orphan drugs by the FDA for monotherapy for pediatric patients with infantile spasms from 1 month to 2 years of age. Vigabatrin is also indicated as the adjunctive therapy for adults and pediatric patients 10 years of age and older with refractory complex partial seizures. Ideally, the vigabatrin treatment entails achieving complete seizure freedom without significant adverse effects, and the therapeutic drug monitoring (TDM) will make a significant contribution to this aim, which provides a pragmatic approach to such epilepsy care in that the dose tailoring can be undertaken for uncontrollable seizures and in cases of clinical toxicity guided by the drug concentrations. Thus, reliable assays are mandatory for TDM to be valuable, and blood, plasma, or serum are the matrixes of choice. In this study, a simple, rapid, and sensitive LC-ESI-MS/MS method for the measurement of plasma vigabatrin was developed and validated. The sample clean-up was performed by an easy-to-use method, i.e., protein precipitation using acetonitrile (ACN). Chromatographic separation of vigabatrin and vigabatrin-¹³C,d₂ (internal standard) was achieved on the Waters symmetry C18 column (4.6 mm × 50 mm, 3.5 μm) with isocratic elution at a flow rate of 0.35 mL min^-1. The target analyte was completely separated by elution with a highly aqueous mobile phase for 5 min, without any endogenous interference. The method showed good linearity over the 0.010-50.0 μg mL^-1 concentration range with a correlation coefficient r² = 0.9982. The intra-batch and inter-batch precision and accuracy, recovery, and stability of the method were all within the acceptable parameters. Moreover, the method was successfully used in pediatric patients treated with vigabatrin and also provided valuable information for clinicians by monitoring plasma vigabatrin levels in our hospital.

Treatment of Infantile Spasm Syndrome: Update from the Interdisciplinary Guideline Committee Coordinated by the German-Speaking Society of Neuropediatrics

OBJECTIVES

The manuscript serves as an update on the current management practices for infantile spasm syndrome (ISS). It includes a detailed summary of the level of current evidence of different treatment options for ISS and gives recommendations for the treatment and care of patients with ISS.

METHODS

A literature search was performed using the Cochrane and Medline Databases (2014 to July 2020). All studies were objectively rated using the Scottish Intercollegiate Guidelines Network. For recommendations, the evidence from these studies was combined with the evidence from studies used in the 2014 guideline.

RECOMMENDATIONS

If ISS is suspected, electroencephalography (EEG) should be performed within a few days and, if confirmed, treatment should be initiated immediately. Response to first-line treatment should be evaluated clinically and electroencephalographically after 14 days. The preferred first-line treatment for ISS consists of either hormone-based monotherapy (AdrenoCorticoTropic Hormone [ACTH] or prednisolone) or a combination of hormone and vigabatrin. Children with tuberous sclerosis complex and those with contraindications against hormone treatment should be treated with vigabatrin. If first-line drugs are ineffective, second-line treatment options such as ketogenic dietary therapies, sulthiame, topiramate, valproate, zonisamide, or benzodiazepines should be considered. Children refractory to drug therapy should be evaluated early for epilepsy surgery, especially if focal brain lesions are present. Parents should be informed about the disease, the efficacy and adverse effects of the medication, and support options for the family. Regular follow-up controls are recommended.

Ocular examinations, findings, and toxicity in children taking vigabatrin

BACKGROUND

The antiepileptic medication vigabatrin has been associated with ocular toxicity, and close ophthalmic monitoring has been recommended; however, there is no clear consensus regarding the value and feasibility of such monitoring in children. We describe ophthalmic assessments in children in a real-world clinical setting, the incidence of vigabatrin-related ocular toxicity, and the utility of regular screening or ancillary testing in children taking vigabatrin.

METHODS

The medical records of children taking vigabatrin with one or more ophthalmic assessments at Children's Hospital of Philadelphia or University of California, San Francisco, between May 2010 and May 2021, were reviewed retrospectively. Abnormalities on ophthalmic examination, visual field (VF), electroretinogram (ERG), and optical coherence tomography (OCT) were reviewed and categorized as attributable to vigabatrin, possibly attributable to vigabatrin, or not attributable to vigabatrin.

RESULTS

A total of 1,281 assessments of 284 children (mean age, 2.09 years) were included. Of these, 283 (99.6%) had funduscopic examination(s), 37 (13.0%) had ERG, 19 (6.7%) had OCT, and 6 (2.1%) had formal VF. Rate of examinations and ERGs per child decreased over the 10-year study period. Two children (0.7%) had definite vigabatrin-related ocular toxicity, both identified on ERG. An additional 4 children (1.4%) had optic atrophy of unclear relation to vigabatrin, categorized as possible toxicity. The remaining 278 children did not have abnormal examination or testing findings attributable to vigabatrin.

CONCLUSIONS

The incidence of vigabatrin-related ocular toxicity in children was low in our cohort. Ocular and neurologic comorbidities and limited examinations in children make identification of such toxicity challenging and the value of screening is unclear.

Real-World Evidence to Assess Medication Safety or Effectiveness in Children: Systematic Review

Background

The promise of real-world evidence (RWE) is especially relevant to pediatrics, where medicines prescribed for children are often used without evidence derived from randomized clinical trials.

Objectives

The aim of this systematic review was to describe the state of RWE in pediatrics by identifying observational studies published during 2016 that used RWE to assess medication safety or effectiveness in children.

Methods

An electronic search of PubMed was combined with an extended search of references within systematic reviews and expert suggestions. Studies were included if they reported on an infant or child under 18 years with exposure to medications; assessed safety or effectiveness; specified a comparison or control group, and were published in English in 2016. Data extraction was conducted by one team member using a standardized form and reviewed by a second team member. Study quality was assessed using the GRACE checklist for rating the quality of observational studies.

Results

After removing duplicates, 915 citations were screened and 29 studies met the eligibility criteria. Most of the eligible studies relied on primary data collection or chart review at a single institution and did not use the growing number of administrative or electronic health record databases available. One-quarter of the studies did not use well-established statistical methods to control for confounders. No single disease group or medication predominated, and age groups ranged from infants to adolescents.

Conclusions

A small body of observational studies published in 2016 were categorized by the study team as using real-world data to assess medication safety or effectiveness in children. Studies varied in age groups, diseases or conditions, and methods, and may not have fully met the FDA definition of RWE. Our review indicates that the use of RWE is not fully developed in pediatrics, and suggests an opportunity to further develop capabilities and more fully leverage administrative and electronic health record databases to study medication safety and effectiveness in children. Our systematic review appears generalizable to pediatrics broadly, and documents that the high level of activity in RWE in general has had less of an impact on pediatrics.

Electronic supplementary material

The online version of this article (10.1007/s40801-020-00182-y) contains supplementary material, which is available to authorized users.

Status Epilepticus Manifested as Continuous Epileptic Spasms

Objective: The etiology and outcome of status epilepticus with continuous epileptic spasms have not been fully understood; and only rare cases have been reported in the literature. Here, we described 11 children, who manifested continuous epileptic spasms with various etiologies and different outcomes. Methods: This is a case series study designed to systematically review the charts, video-electroencephalography (video-EEG), magnetic resonance images, and longitudinal follow-up of patients who presented continuous epileptic spasms lasting more than 30 min. Results: Median age at onset was 2 years old, ranging from 2 months to 5.6 years. The etiology of continuous epileptic spasms for these 11 cases consisted of not only some known electro-clinical epilepsy syndromes like West Syndrome and Ohtahara Syndrome, but also secondary symptomatic continuous epileptic spasms, caused by acute encephalitis or encephalopathy, which extends the etiological spectrum of continuous epileptic spasms. The most characteristic feature of these 11 cases was prolonged epileptic spasms, lasting for a median of 13.00 days (95% CI: 7.26-128.22 days). The interictal EEG findings typically manifested as hypsarrhythmia or its variants, including burst suppression. Hospital stays were much longer in acute symptomatic cases than in primary epileptic syndromic cases (59.67 ± 50.82 vs. 15.00 ± 1.41 days). However, the long-term outcomes were extremely poor in the patients with defined electro-clinical epilepsy syndromes, including severe motor and intellectual developmental deficits (follow-up of 4.94 ± 1.56 years), despite early diagnosis and treatment. Continuous epileptic spasms were refractory to corticosteroids, immuno-modulation or immunosuppressive therapies, and ketogenic diet. Conclusion: Continuous epileptic spasms were associated with severe brain impairments in patients with electro-clinical syndromes; and required long hospital stays in patients with acute symptomatic causes. We suggest to include continuous epileptic spasms in the international classification of status epilepticus, as a special form. Further investigations are required to better recognize this condition, better understand the etiology, as well as to explore more effective treatments to improve outcomes.

Metabolomic analyses of vigabatrin (VGB)-treated mice: GABA-transaminase inhibition significantly alters amino acid profiles in murine neural and non-neural tissues

The anticonvulsant vigabatrin (VGB; Sabril^R) irreversibly inhibits GABA transaminase to increase neural GABA, yet its mechanism of retinal toxicity remains unclear. VGB is suggested to alter several amino acids, including homocarnosine, β-alanine, ornithine, glycine, taurine, and 2-aminoadipic acid (AADA), the latter a homologue of glutamic acid. Here, we evaluate the effect of VGB on amino acid concentrations in mice, employing a continuous VGB infusion (subcutaneously implanted osmotic minipumps), dose-escalation paradigm (35-140 mg/kg/d, 12 days), and amino acid quantitation in eye, visual and prefrontal cortex, total brain, liver and plasma. We hypothesized that continuous VGB dosing would reveal numerous hitherto undescribed amino acid disturbances. Consistent amino acid elevations across tissues included GABA, β-alanine, carnosine, ornithine and AADA, as well as neuroactive aspartic and glutamic acids, serine and glycine. Maximal increase of AADA in eye occurred at 35 mg/kg/d (41 ± 2 nmol/g (n = 21, vehicle) to 60 ± 8.5 (n = 8)), and at 70 mg/kg/d for brain (97 ± 6 (n = 21) to 145 ± 6 (n = 6)), visual cortex (128 ± 6 to 215 ± 19) and prefrontal cortex (124 ± 11 to 200 ± 13; mean ± SEM; p < 0.05), the first demonstration of tissue AADA accumulation with VGB in mammal. VGB effects on basic amino acids, including guanidino-species, suggested the capacity of VGB to alter urea cycle function and nitrogen disposal. The known toxicity of AADA in retinal glial cells highlights new avenues for assessing VGB retinal toxicity and other off-target effects.

Preclinical tissue distribution and metabolic correlations of vigabatrin, an antiepileptic drug associated with potential use-limiting visual field defects

Vigabatrin (VGB; (S)-(+)/(R)-(-) 4-aminohex-5-enoic acid), an antiepileptic irreversibly inactivating GABA transaminase (GABA-T), manifests use-limiting ocular toxicity. Hypothesizing that the active S enantiomer of VGB would preferentially accumulate in eye and visual cortex (VC) as one potential mechanism for ocular toxicity, we infused racemic VGB into mice via subcutaneous minipump at 35, 70, and 140 mg/kg/d (n = 6-8 animals/dose) for 12 days. VGB enantiomers, total GABA and β-alanine (BALA), 4-guanidinobutyrate (4-GBA), and creatine were quantified by mass spectrometry in eye, brain, liver, prefrontal cortex (PFC), and VC. Plasma VGB concentrations increased linearly by dose (3 ± 0.76 (35 mg/kg/d); 15.1 ± 1.4 (70 mg/kg/d); 34.6 ± 3.2 μmol/L (140 mg/kg/d); mean ± SEM) with an S/R ratio of 0.74 ± 0.02 (n = 14). Steady state S/R ratios (35, 70 mg/kg/d doses) were highest in eye (5.5 ± 0.2; P < 0.0001), followed by VC (3.9 ± 0.4), PFC (3.6 ± 0.3), liver (2.9 ± 0.1), and brain (1.5 ± 0.1; n = 13-14 each). Total VGB content of eye exceeded that of brain, PFC and VC at all doses. High-dose VGB diminished endogenous metabolite production, especially in PFC and VC. GABA significantly increased in all tissues (all doses) except brain; BALA increases were confined to liver and VC; and 4-GBA was prominently increased in brain, PFC and VC (and eye at high dose). Linear correlations between enantiomers and GABA were observed in all tissues, but only in PFC/VC for BALA, 4-GBA, and creatine. Preferential accumulation of the VGB S isomer in eye and VC may provide new insight into VGB ocular toxicity.

Treatment of infantile spasms

The treatment of infantile spasms is challenging, especially in the context of the following: (1) a severe phenotype with high morbidity and mortality; (2) the urgency of diagnosis and successful early response to therapy; and (3) the paucity of effective, safe, and well-tolerated therapies. Even after initially successful treatment, relapse risk is substantial and the most effective therapies pose considerable risk with long-term administration. In evaluating any treatment for infantile spasms, the key short-term outcome measure is freedom from both epileptic spasms and hypsarrhythmia. In contrast, the most important long-term outcomes are enduring seizure-freedom and measures of intellectual performance in later childhood and adulthood. First-line treatment options-namely hormonal therapy and vigabatrin-display moderate to high efficacy but also exhibit substantial side-effect burdens. Data on efficacy and safety of each class of therapy, as well as the combination of these therapies, are reviewed in detail. Specific hormonal therapies (adrenocorticotropic hormone and various corticosteroids) are contrasted. Those etiologies that prompt specific therapies are reviewed briefly, as are an array of second-line therapies supported by less-compelling data. The ketogenic diet is discussed in greater detail, with a focus on the limitations of numerous available studies that generally suggest that it is efficacious. Special discussion is allocated to cannabidiol-the investigational therapy that has received the most attention, and which is already in use in the form of various artisanal cannabis extracts. Finally, a treatment algorithm reflecting the concepts and controversies discussed in this review is presented.

High vigabatrin dosage is associated with lower risk of infantile spasms relapse among children with tuberous sclerosis complex

After initially successful treatment of infantile spasms, the long-term cumulative risk of relapse approaches 50%, and there is no established protocol to mitigate this risk. Although vigabatrin may be an effective means to prevent relapse, there is little guidance as to ideal duration and dosage. Using a cohort of children with infantile spasms and tuberous sclerosis complex (TSC), we evaluated the potential association of post-response VGB treatment and the rate of infantile spasms relapse. Patients with infantile spasms and clinical response to vigabatrin were identified among a multicenter prospective observational cohort of children with TSC. For each patient we recorded dates of infantile spasms onset, response to vigabatrin, relapse (if any), and quantified duration and dosage of vigabatrin after response. Time to relapse as a function of vigabatrin exposure was evaluated using survival analyses. We identified 50 children who responded to VGB. During a median follow-up of 16.6 months (IQR 10.3-22.9), 12 (24%) patients subsequently relapsed after a median of 7.8 months (IQR 3.1-9.6). Relapse occurred after VGB discontinuation in four patients, and during continued VGB treatment in the remaining eight cases. In survival analyses, risk of relapse was unaffected by the presence or absence of VGB treatment (HR 0.31, 95%CI 0.01-28.4, P =  0.61), but weighted-average dosage was associated with marked reduction in relapse risk: Each 50 mg/kg/d increment in dosage was associated with 61% reduction in risk (HR 0.39, 95%CI 0.17 - 0.90, P =  0.026). This study suggests that the risk of infantile spasms relapse in TSC may be reduced by high-dose vigabatrin treatment.

Management of epilepsy associated with tuberous sclerosis complex: Updated clinical recommendations

Patients with tuberous sclerosis complex (TSC) are at very high risk for developing epilepsy, and the majority experience seizure onset during the first year of life. Early targeted interventions increase the probability of seizure-freedom and may protect neurodevelopment. In 2012, clinical recommendations for the management of epilepsy in patients with TSC were published by a panel of European experts. Since that time novel studies, reports, and expert opinions in preclinical and clinical TSC-related sciences prompted the need for updated recommendations, including epileptogenesis in TSC, the potential role of predictive biomarkers, the possible benefits of presymptomatic diagnosis and preventive treatment, and new treatment options including mTOR inhibitors. A reconvened panel reviewed the current literature to answer specific questions and five panelists discussed the findings, followed by a general discussion during which all issues were debated to achieve consensus regarding recommendations. A draft manuscript based on these discussions and recommendations was then circulated several times among the panelists, who added their own comments. All the panelists/authors agreed with the final manuscript, which was then submitted for publication. The panel concluded that the need for early diagnosis of TSC-associated seizures is now established, electroencephalographic monitoring has good predictive value for epilepsy before seizure onset in TSC, and, until conclusive data from the EPISTOP trial are available, administration of vigabatrin may be considered in children with subclinical epileptiform EEG discharges. The panel also supported the role of adjunctive everolimus for TSC-associated drug-refractory seizures and emphasized the necessity of early surgical evaluation.

Epileptic Encephalopathies

PURPOSE OF REVIEW

This article reviews the manifestations and treatment of the epileptic encephalopathies, which are a heterogeneous group of disorders characterized by both seizures and neurocognitive impairment.

RECENT FINDINGS

Next-generation (exome- and genome-based) sequencing technologies are revolutionizing the identification of single-gene causes of epileptic encephalopathy but have only had a modest impact on patient-specific treatment decisions. The treatment of most forms of epileptic encephalopathy remains a particularly challenging endeavor, with therapeutic decisions chiefly driven by the electroclinical syndrome classification. Most antiseizure drugs are ineffective in the treatment of these disorders, and treatments that are effective often entail significant risk and cost.

SUMMARY

The epileptic encephalopathies continue to pose a major challenge in diagnosis and treatment, with most patients experiencing very poor outcomes, although a significant minority of patients respond to, or are even cured by, specific therapies.

Efficacy and safety of vigabatrin in Japanese patients with infantile spasms: Primary short-term study and extension study

Vigabatrin was approved for the treatment of infantile spasms by the US Food and Drug Administration, but not in Japan at the time of initiating this clinical study because of concerns about irreversible peripheral visual field defects (VFDs). This study evaluated the efficacy and safety of vigabatrin for Japanese patients with infantile spasms. Of 15 patients (aged ≥4weeks and <2years) enrolled, with the exception of two patients who did not receive vigabatrin, 13 were treated with a titrated dosage of vigabatrin (50-150mg/kg/day; limited to 3000mg/day). Twelve out of 13 patients receiving vigabatrin had spasms that were treatment refractory; these patients were concurrently treated with at least one other antiepileptic drug. One patient received vigabatrin monotherapy. Eight of the 13 patients (61.5% [95% CI: 31.6-86.1%]) had a ≥50% reduction during the dose-adjustment phase compared with baseline in the frequency of spasms, with efficacy maintained through a 2-week maintenance phase. Spasms disappeared in six out of nine patients (66.7% [95% CI: 29.9-92.5%]) who transitioned to the maintenance phase and hypsarrhythmia on electroencephalography also resolved in four patients. Hypsarrhythmia was improved in another two patients. Six out of seven patients who continued treatment through Week 32 of an extension study reported ongoing efficacy for vigabatrin. The most common adverse events (AEs) were psychiatric disorders and nervous system disorders (n=8; 61.5%) that were generally mild in severity. No treatment-related peripheral VFDs were observed. No severe AEs or AEs resulting in discontinuation of vigabatrin therapy were reported. An abnormality in magnetic resonance images was observed in one patient during the extension period. Vigabatrin was deemed to be clinically effective and well tolerated in Japanese patients with infantile spasms.