Tiagabine-related non-convulsive status epilepticus in partial epilepsy: three case reports and a review of the literature

Tiagabine-induced encephalopathy suppressed by vagus nerve stimulation: A case report

Tiagabine has been associated with reports of status epilepticus as well as encephalopathy, even when used within therapeutic doses. Vagus nerve stimulation (VNS) has been used successfully to reduce seizure frequency in the outpatient setting as well as in the acute setting of status epilepticus. It is also theorized to reduce cortical synchronization. We present a case of a patient on adjunctive tiagabine therapy who developed sudden onset encephalopathy and rhythmic delta activity soon after vagus nerve stimulation was turned off in preparation for magnetic resonance imaging. The bilateral rhythmic delta activity significantly reduced in burden after VNS was turned back on and encephalopathy also gradually improved to baseline. We hypothesize that vagus nerve stimulation successfully interrupted diffuse hypersynchrony, in the form of bilateral rhythmic delta activity, caused by tiagabine. To our knowledge, this is the first report of such a phenomenon.

New GABA-Targeting Therapies for the Treatment of Seizures and Epilepsy: I. Role of GABA as a Modulator of Seizure Activity and Recently Approved Medications Acting on the GABA System

γ-Aminobutyric acid (GABA) is the most prevalent inhibitory neurotransmitter in the mammalian brain and has been found to play an important role in the pathogenesis or the expression of many neurological diseases, including epilepsy. Although GABA can act on different receptor subtypes, the component of the GABA system that is most critical to modulation of seizure activity is the GABAA-receptor-chloride (Cl-) channel complex, which controls the movement of Cl- ions across the neuronal membrane. In the mature brain, binding of GABA to GABAA receptors evokes a hyperpolarising (anticonvulsant) response, which is mediated by influx of Cl- into the cell driven by its concentration gradient between extracellular and intracellular fluid. However, in the immature brain and under certain pathological conditions, GABA can exert a paradoxical depolarising (proconvulsant) effect as a result of an efflux of chloride from high intracellular to lower extracellular Cl- levels. Extensive preclinical and clinical evidence indicates that alterations in GABAergic inhibition caused by drugs, toxins, gene defects or other disease states (including seizures themselves) play a causative or contributing role in facilitating or maintaning seizure activity. Conversely, enhancement of GABAergic transmission through pharmacological modulation of the GABA system is a major mechanism by which different antiseizure medications exert their therapeutic effect. In this article, we review the pharmacology and function of the GABA system and its perturbation in seizure disorders, and highlight how improved understanding of this system offers opportunities to develop more efficacious and better tolerated antiseizure medications. We also review the available data for the two most recently approved antiseizure medications that act, at least in part, through GABAergic mechanisms, namely cenobamate and ganaxolone. Differences in the mode of drug discovery, pharmacological profile, pharmacokinetic properties, drug-drug interaction potential, and clinical efficacy and tolerability of these agents are discussed.

Atypical or Typical Triphasic Waves-Is There a Difference? A Review

SUMMARY

The entity of triphasic waves (TWs) and TW encephalopathy has derived from the subjective art of EEG interpretation. Indeed, there are few if any guidelines regarding many different aspects of TWs. The authors seek to shed light on the nature and the diagnostic characteristics of various types of TWs, differentiating "typical" from "atypical" forms. The authors conclude that morphologies in the form of bursts of well-formed, smoothly contoured, negative-positive-negative, bilateral, symmetrical and synchronous, regular, reactive, periodic or rhythmic, 1.5 to 2.0 Hz, fronto-central, triphasic complexes with fronto-occipital lag meet the criteria for typical TWs and are highly suggestive of toxic-metabolic encephalopathies. These are most frequently hepatic, uremic, or sepsis-associated encephalopathies with multi-organ failure. In such cases, atypical TWs (frontopolar or parieto-occipital maximum, negative-positive or negative-positive-negative, asymmetric and asynchronous, unreactive, irregular, multifocal, continuous with spatiotemporal evolution, sharper and without fronto-occipital/occipito-frontal lag, or triphasic delta waves) are rarely seen. Atypical TWs are encountered in Angelman syndrome, toxic encephalopathies, hyperthyroidism/hypothyroidism, Hashimoto encephalopathy, nonconvulsive status epilepticus, dementia, sepsis-associated encephalopathy, cerebrovascular disorders, and certain boundary syndromes. Investigations describing TWs with uncommon etiologies revealed few with typical TWs, suggesting that the term "TWs" has been overused in the past. Triphasic waves arise from the interaction of multiple factors including toxic, metabolic, infectious, and structural disorders that affect circuits between thalamus and cortex. The patient's metabolic status, presence of potentially neurotoxic drugs, cerebral atrophy, white matter disease, dementia, or seizures help differentiate typical from typical TWs. Future studies will determine whether this dichotomy is heuristically and clinically helpful.

Tiagabine-related status epilepticus: a case report and systematic literature review

Tiagabine-related status epilepticus (SE) is an uncommon complication of tiagabine use. We aimed to detail the features and outcomes in a patient with tiagabine poisoning and review the relevant literature. We describe a case of tiagabine-related SE and literature review based on a 1995-2019 PubMed search. We report the case of a 30-year-old man with super-refractory SE after tiagabine poisoning. He fully recovered after 72 h of general anesthesia and was discharged from the ICU on day 16. A literature review showed distinct features among patients with tiagabine-related SE. Tiagabine side effects were characterized by non-convulsive SE after a slight increase in tiagabine dose and a rapid favorable evolution after benzodiazepine and early tiagabine withdrawal. Generalized convulsive SE was a complication of voluntary or involuntary tiagabine poisoning and was particularly refractory. Both presentations are characterized by a return to baseline after prompt and adequate management. Tiagabine-related SE electroclinical features vary according to the underlying pathophysiological mechanism and can be life threatening. Recovery is the rule after tiagabine withdrawal and SE management with progressive therapeutic escalation guided by response to prior anticonvulsant treatments.

Pregabalin induced visual hallucinations - a rare adverse reaction

Background

Pregabalin is an anticonvulsive, analgesic and anxiolytic medication. The typical side effects include dizziness, somnolence and weight gain. Few studies or case reports have demonstrated psychiatric side effects resulting from its use.

Case presentation

We present a patient who suffered visual hallucinations and agitation associated with an increase in pregabalin dose, resolving completely after pregabalin discontinuation.

Conclusions

Acute visual hallucinations should be considered in the clinical spectrum of very rare side effects of pregabalin use, especially at higher doses. Tapered discontinuation of the medication can improve and resolve symptoms.

Advances in anti-epileptic drug testing

In the past twenty-one years, 17 new antiepileptic drugs have been approved for use in the United States and/or Europe. These drugs are clobazam, ezogabine (retigabine), eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, perampanel, pregabalin, rufinamide, stiripentol, tiagabine, topiramate, vigabatrin and zonisamide. Therapeutic drug monitoring is often used in the clinical dosing of the newer anti-epileptic drugs. The drugs with the best justifications for drug monitoring are lamotrigine, levetiracetam, oxcarbazepine, stiripentol, and zonisamide. Perampanel, stiripentol and tiagabine are strongly bound to serum proteins and are candidates for monitoring of the free drug fractions. Alternative specimens for therapeutic drug monitoring are saliva and dried blood spots. Therapeutic drug monitoring of the new antiepileptic drugs is discussed here for managing patients with epilepsy.

Tiagabine in clinical practice: effects on seizure control and behavior

OBJECTIVE

Preapproval randomized controlled trials of antiepileptic drugs provide data in limited patient groups. We assessed the side effect and seizure reduction profile of tiagabine (TGB) in typical clinical practice.

METHODS

Investigators recorded adverse effect (AE), seizure, and assessment-of-benefit data prospectively in sequential patients treated open label with TGB.

RESULTS

Two hundred ninety-two patients (39 children) were enrolled to be treated long term with TGB. Seizure types were focal-onset (86%), generalized-onset (12%), both focal- and generalized-onset (0.3%), and multiple associated with Lennox-Gastaut Syndrome (2%). Two hundred thirty-one received at least one dose of TGB (median = 28 mg/day) and had follow-up seizure or AE data reported. Common AEs were fatigue, dizziness, psychomotor slowing, ataxia, gastrointestinal upset, weight change, insomnia, and "others" (mostly behavioral). Serious AEs occurred in 19 patients: behavioral effects (n = 12), status epilepticus (n = 3), others (n = 3), and sudden unexplained death (n = 1). No patients experienced suicidal ideation/behavior, rash, nephrolithiasis, or organ failure. Seizure outcomes were seizure freedom (5%), ≥75% reduction (12%), ≥50% reduction (23%), and increased number of seizures (17%), or new seizure type (1%).

CONCLUSIONS

Behavioral AEs occurred in a larger proportion of patients compared to those reported in TGB preapproval randomized controlled trials. A moderate percentage of patients had a meaningful reduction in seizure frequency. In clinical practice, TGB remains a useful antiepileptic drug.

Tiagabine-induced stupor in patients with psychogenic nonepileptic seizures: nonconvulsive status epilepticus or encephalopathy?

BACKGROUND

Nonconvulsive status epilepticus has been rarely reported with tiagabine (TGB) use.

METHODS

We report findings from continuous video-EEG monitoring and serial neurological examinations during prolonged episodes of stupor associated with TGB use in three patients who did not have epilepsy.

RESULTS

All three patients had emergence of new type of events after starting TGB treatment. All three patients had gradual decline in responsiveness to verbal stimuli, intermittent twitching of the upper extremities, and urinary incontinence. The corresponding EEG showed gradual build-up of generalized bisynchronous delta-wave activity with subsequent intermingled sharp transients. Two patients did not respond to IV lorazepam, one of whom also did not respond to IV phenytoin. The EEG slowly normalized in conjunction with associated clinical improvement. Habitual seizures were found to be psychogenic, with no interictal evidence for epilepsy.

CONCLUSION

Tiagabine-related stupor may represent a form of toxic encephalopathy in some cases rather than nonconvulsive status epilepticus.

Tiagabine for acute affective episodes in bipolar disorder

BACKGROUND

Bipolar disorder is a common recurrent illness with high levels of chronicity. Treatment resistance persists despite the use of established medications, such as lithium and valproate. New medications are required for the treatment of refractory cases. Some open-label reports have suggested that the anticonvulsant tiagabine may be efficacious in bipolar disorder. There is a need to clarify the evidence available, in the form of randomised controlled trials, for its use in the treatment of acute affective episodes in bipolar disorder.

OBJECTIVES

To review the evidence for the efficacy and acceptability of tiagabine in the treatment of acute mood episodes in bipolar disorder.

SEARCH METHODS

In this update, we searched the Cochrane Depression, Anxiety and Neurosis Group's Specialised Register (CCDANCTR-Studies and CCDANCTR-References) to October 2012. This register contains relevant randomised controlled trials from: The Cochrane Library (all years), EMBASE (1974 to date), MEDLINE (1950 to date) and PsycINFO (1967 to date). We examined reference lists of relevant papers and major textbooks of affective disorder. We contacted authors, other experts in the field and pharmaceutical companies for knowledge of suitable published or unpublished trials. We handsearched specialist journals and conference proceedings.

SELECTION CRITERIA

Randomised controlled trials, which compared tiagabine with placebo or with active agents in the treatment of any acute mood episodes in bipolar disorder in adults, male and female, aged 18 to 74 years.

DATA COLLECTION AND ANALYSIS

Two review authors performed data extraction and methodological quality assessment independently. For analysis, we planned to use risk ratio for binary efficacy outcomes and mean difference or standardised mean difference for continuously distributed outcomes.

MAIN RESULTS

In this updated review we found no studies which fulfilled the Cochrane criteria for randomised controlled trials.

AUTHORS' CONCLUSIONS

We found no randomised controlled trials of tiagabine in the treatment of acute episodes of bipolar disorder. However, there are reports that a number of patients suffered episodes of syncope or seizure. Further investigation of the efficacy and acceptability of tiagabine in the treatment of acute affective episodes of bipolar disorder should await the clarification of the nature of the reported episodes of syncope and seizure-like activity and an examination of the level of risk involved.

Antiepileptic drug therapy: does mechanism of action matter?

This article represents a synthesis of presentations made by the authors during a scientific meeting held in London on 7 June 2010 and organized by GlaxoSmithKline. Each speaker produced a short précis of his lecture to answer a specific question, resulting in an overview of what we know about the relevance of the mechanisms of action of antiepileptic drugs in determining appropriate combination therapies for the treatment of drug-resistant epilepsy.

Selected pharmacokinetic issues of the use of antiepileptic drugs and parenteral nutrition in critically ill patients

OBJECTIVES

To conduct a systematic review for the evidence supporting or disproving the reality of parenteral nutrition- antiepileptic drugs interaction, especially with respect to the plasma protein-binding of the drug.

METHODS

The articles related to the topic were identified through Medline and PubMed search (1968-Feburary 2010) for English language on the interaction between parenteral nutrition and antiepileptic drugs; the search terms used were anti-epileptic drugs, parenteral nutrition, and/or interaction, and/or in vitro. The search looked for prospective randomized and nonrandomized controlled studies; prospective nonrandomized uncontrolled studies; retrospective studies; case reports; and in vitro studies. Full text of the articles were then traced from the Universiti Sains Malaysia (USM) library subscribed databases, including Wiley-Blackwell Library, Cochrane Library, EBSCOHost, OVID, ScienceDirect, SAGE Premier, Scopus, SpringerLINK, and Wiley InterScience. The articles from journals not listed by USM library were traced through inter library loan.

RESULTS

There were interactions between parenteral nutrition and drugs, including antiepileptics. Several guidelines were designed for the management of illnesses such as traumatic brain injuries or cancer patients, involving the use of parenteral nutrition and antiepileptics. Moreover, many studies demonstrated the in vitro and in vivo parenteral nutrition -drugs interactions, especially with antiepileptics.

CONCLUSIONS

There was no evidence supporting the existence of parenteral nutrition-antiepileptic drugs interaction. The issue has not been studied in formal researches, but several case reports and anecdotes demonstrate this drug-nutrition interaction. However, alteration in the drug-free fraction result from parenteral nutrition-drug (i.e. antiepileptics) interactions may necessitate scrupulous reassessment of drug dosages in patients receiving these therapies. This reassessment may be particularly imperative in certain clinical situations characterized by hypoalbuminemia (e.g., burn patients).

The uncommon causes of status epilepticus: a systematic review

This paper reports the first systematic review of uncommon causes of status epilepticus reported in the literature between 1990 and 2008. Uncommon causes are defined as those not listed in the main epidemiological studies of status epilepticus. 181 causes were identified. These were easily categorised into 5 specific aetiological categories: immunological disorders, mitochondrial disorders, infectious diseases, genetic disorders and drugs/toxins. A sixth category of 'other causes' has also been included. Knowledge of these causes is important for clinical management and treatment, and also for a better understanding of the pathophysiology of status epilepticus.

Therapeutic Drug Monitoring of the Newer Anti-Epilepsy Medications

In the past twenty years, 14 new antiepileptic drugs have been approved for use in the United States and/or Europe. These drugs are eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, pregabalin, rufinamide, stiripentol, tiagabine, topiramate, vigabatrin and zonisamide. In general, the clinical utility of therapeutic drug monitoring has not been established in clinical trials for these new anticonvulsants, and clear guidelines for drug monitoring have yet to be defined. The antiepileptic drugs with the strongest justifications for drug monitoring are lamotrigine, oxcarbazepine, stiripentol, and zonisamide. Stiripentol and tiagabine are strongly protein bound and are candidates for free drug monitoring. Therapeutic drug monitoring has lower utility for gabapentin, pregabalin, and vigabatrin. Measurement of salivary drug concentrations has potential utility for therapeutic drug monitoring of lamotrigine, levetiracetam, and topiramate. Therapeutic drug monitoring of the new antiepileptic drugs will be discussed in managing patients with epilepsy.

Therapeutic Drug Monitoring of the Newer Anti-Epilepsy Medications

In the past twenty years, 14 new antiepileptic drugs have been approved for use in the United States and/or Europe. These drugs are eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, pregabalin, rufinamide, stiripentol, tiagabine, topiramate, vigabatrin and zonisamide. In general, the clinical utility of therapeutic drug monitoring has not been established in clinical trials for these new anticonvulsants, and clear guidelines for drug monitoring have yet to be defined. The antiepileptic drugs with the strongest justifications for drug monitoring are lamotrigine, oxcarbazepine, stiripentol, and zonisamide. Stiripentol and tiagabine are strongly protein bound and are candidates for free drug monitoring. Therapeutic drug monitoring has lower utility for gabapentin, pregabalin, and vigabatrin. Measurement of salivary drug concentrations has potential utility for therapeutic drug monitoring of lamotrigine, levetiracetam, and topiramate. Therapeutic drug monitoring of the new antiepileptic drugs will be discussed in managing patients with epilepsy.

An alternative perspective on the management of status epilepticus

The definition of status epilepticus (SE) has been reduced from 30 minutes to 5 minutes and this article questions if treatment should not be offered before reaching that window. After provision of first aid, benzodiazepines (BDZ) are the initial form of intervention, with either nasal or buccal midazolam being favored for nonprofessionals. Proper patient supervision, including admission to an intensive care unit for more difficult patients, is endorsed, and the need to warn nonprofessionals of the potential risk of respiratory depression is imperative. The article criticizes the use of phenytoin as the antiepileptic medication (AEM) with which to load patients, as it is no longer a first-line AEM, and argues in favor of using a first-line AEM such as valproate or carbamazepine, or preferably the AEM that previously proved efficacious in a patient with known epilepsy who was noncompliant. Alternative routes of administration of AEMs are discussed, and the use of blood level monitoring, as an adjunct to management, to protect against further episodes of SE, is supported. Touched on in this article are the use of some of the newer AEMs in the management of SE and exploration of treatment strategies that acknowledge that treatment must also include patient education that incorporates techniques to enhance compliance.

Seizures in a pediatric patient with a tiagabine overdose

INTRODUCTION

Tiagabine (TGB) is a novel antiepileptic that decreases GABA uptake. The literature contains one report of an adult with epilepsy who ingested up to 1 gram of TGB and developed status epilepticus. We reported on a pediatric patient who ingested significantly less TGB but still developed tonic-clonic seizures.

CASE REPORT

A previously healthy, 13 kg, two-year-old girl developed generalized tonic-clonic seizure activity at home approximately 1 hour after ingesting 90 mg of her grandmother's TGB (forty five 2 mg tablets). At the hospital she had two 5 minute seizures at 1.5 and 3.5 hours post ingestion. Her serum TGB levels were 530 and 130 ng/ml approximately 5 and 11 hours post-ingestion (5-70 ng/ml trough levels with most probable range for seizure control). She was discharged 27 hours post ingestion, and she was in good condition.

CONCLUSION

An overdose of TGB, a novel anti-epileptic, can cause convulsive seizures.

Currently available antiepileptic drugs

Many new antiepileptic drugs (AEDs) have become available over the past 15 years. At the same time, the emphasis on treating patients with epilepsy has grown from stopping seizures to avoiding side effects and maximizing quality of life. This review summarizes currently available AEDs, and presents general treatment principles and guidelines for AED selection. Unfortunately, despite the increased treatment options of today, seizure freedom without side effects remains unattainable for too many patients with epilepsy. Consequently, there remains a significant need for further development of new therapies.

Characterization of the Anticonvulsant, Behavioral and Pharmacokinetic Interaction Profiles of Stiripentol in Combination with Clonazepam, Ethosuximide, Phenobarbital, and Valproate Using Isobolographic Analysis

PURPOSE

Isobolographic analysis was used to characterize the interactions between stiripentol (STP) and clonazepam (CZP), ethosuximide (ETS), phenobarbital (PB), and valproate (VPA) in suppressing pentylenetetrazole (PTZ)-induced clonic seizures in mice.

METHODS

The anticonvulsant and acute adverse (neurotoxic) effects of STP in combination with the various conventional antiepileptic drugs (AEDs), at fixed ratios of 1:3, 1:1, and 3:1, were evaluated in the PTZ and chimney tests in mice using the isobolographic analysis. Additionally, protective indices (PI) and benefit indices (BI) were calculated to identify their pharmacological profiles so that a ranking in relation to advantageous combination could be established. Moreover, adverse-effect paradigms were determined by use of the step-through passive avoidance task (long-term memory), threshold for the first pain reaction, grip-strength test (neuromuscular tone), and the hot plate test (acute thermal pain). Brain AED concentrations were also measured so as to ascertain any pharmacokinetic contribution to the pharmacodynamic interactions.

RESULTS

All AED combinations comprising of STP and CZP, ETS, PB, and VPA (at the fixed ratios of 1:3, 1:1 and 3:1) were additive in terms of clonic seizure suppression in the PTZ test. However, these interactions were complicated by changes in brain AED concentrations consequent to pharmacokinetic interactions. Thus STP significantly increased total brain ETS and PB concentrations, and decreased VPA concentrations, but was without effect on CZP concentrations. In contrast, PB significantly decreased and VPA increased total brain STP concentrations while CZP and ETS were without effect. Furthermore, while isobolographic analysis revealed that STP and CZP in combination, at the fixed ratios of 1:1 and 3:1, were supraadditive (synergistic; p < 0.05), the combinations of STP with CZP (1:3), ETS, PB, or VPA (at all fixed ratios of 1:3, 1:1, and 3:1) were barely additivity in terms of acute neurotoxic adverse effects in the chimney test. Additionally, none of the examined combinations of STP with conventional AEDs (CZP, ETS, PB, VPA--at their median effective doses from the PTZ-test) affected long-term memory, threshold for the first pain reaction, neuromuscular tone, and acute thermal pain.

CONCLUSIONS

Based on BI values, the combination of STP with PB at the fixed ratio of 1:3 appears to be a particularly favourable combination. In contrast, STP and CZP or ETS (at the fixed ratios of 1:1 and 3:1) were unfavorable combinations. However, these conclusions are confounded by the fact that STP is associated with significant pharmacokinetic interactions. The remaining combinations of STP with PB (1:1 and 3:1), CZP (1:3), ETS (1:3), and VPA (at all fixed ratios of 1:3, 1:1, and 3:1) do not appear to be potential favorable AED combinations.

Tiagabine in the treatment of acute affective episodes in bipolar disorder: efficacy and acceptability

BACKGROUND

Bipolar disorder is a common recurrent illness with high levels of chronicity. Treatment resistance persists despite the use of established medications, such as lithium and valproate. New medications are required for the treatment of refractory cases. Some open-label reports have suggested that the anticonvulsant tiagabine may be efficacious in bipolar disorder. There is a need to clarify the evidence available, in the form of randomised controlled trials, for its use in the treatment of acute affective episodes in bipolar disorder

OBJECTIVES

To review the evidence for the efficacy and acceptability of tiagabine in the treatment of acute mood episodes in bipolar disorder.

SEARCH STRATEGY

The following databases were searched on 13-10-2005. The Cochrane Collaboration Depression, Anxiety and Neurosis Controlled Trials Registers (CCDANCTR-Studies and CCDANCTR-References),The Cochrane Controlled Clinical Trials Register (CCCTR),EMBASE,MEDLINE,LILACS,PsycLIT andPsyndex. Reference lists of relevant papers and major textbooks of mood disorder were searched. Handsearches were done (specialist journals and conference proceedings). Authors, other experts in the field and pharmaceutical companies were contacted for knowledge of suitable published or unpublished trials.

SELECTION CRITERIA

Randomised controlled trials, which compared tiagabine with placebo or with active agents in the treatment of any acute mood episodes in bipolar disorder, were selected. Studies of participants with bipolar disorder were to be included. Subjects could be of either sex and of all ages.

DATA COLLECTION AND ANALYSIS

Data extraction and methodological quality assessment were performed independently by two reviewers. For analysis, relative risk was used for binary efficacy outcomes and the weighted mean difference or standardised mean differerence was used for continuously distributed outcomes

MAIN RESULTS

We did not find any studies which fulfilled the Cochrane criteria of randomised controlled trials. However, one uncontrolled open label study and one case series were found. There were also three case reports/series of acute treatment which were continued into maintenance therapy, and one open non-randomised study with this design. The results of these studies are inconsistent.

AUTHORS' CONCLUSIONS

We found no randomised controlled trials of tiagabine in bipolar disorder. In the reported cases, a significant proportion of patients suffered episodes of syncope or seizure. There is a need for randomised controlled trials examining the efficacy and acceptability of tiagabine in the acute treatment of bipolar disorder, after the nature of these episodes has been clarified.

Management of Seizures in the Critically Ill

Seizures in a critically ill patient are not infrequent phenomena. Physicians are perplexed by the wide range of possible cranial or extracranial etiologies, alerted by the risk for further crucial organ compromise if seizures recur, and confused about the treatment options in an environment rich in complex drug interactions and multiple organ dysfunction. The advent of an armamentarium containing multiple new antiepileptic medications complicates the situation further, since several of them have less known mechanisms of action, side effects, or interactions with other intensive care unit (ICU) medications. This review contains useful information regarding the most common etiologies and treatment options for intensivists, consulting neurologists, neurosurgeons, or other specialized physicians treating ICU patients with seizures.

Pregabalin Exerts Oppositional Effects on Different Inhibitory Circuits in Human Motor Cortex: A Double-blind, Placebo-controlled Transcranial Magnetic Stimulation Study

PURPOSE

To explore acute effects of pregabalin (PGB) on human motor cortex excitability with transcranial magnetic stimulation (TMS).

METHODS

PGB, 600 mg/day, was orally administered in 19 healthy subjects twice daily in a randomized, double-blind, placebo-controlled crossover design. Several measures of motor cortex excitability were tested with single- and paired-pulse TMS.

RESULTS

Mean short-interval intracortical inhibition (SICI) was reduced after PGB (74 +/- 7% of unconditioned response) compared with placebo (60 +/- 6% of unconditioned response). In contrast, mean long-interval intracortical inhibition (LICI) was increased by PGB (26 +/- 4% of unconditioned response) compared with placebo (45 +/- 8% of unconditioned response), and mean cortical silent period (CSP) showed an increase from 139 +/- 8 ms or 145 +/- 8 ms after placebo to 162 +/- 7 ms or 161 +/- 10 ms after PGB. Motor thresholds, intracortical facilitation, and corticospinal excitability were unaffected.

CONCLUSIONS

The observed excitability changes with oppositional effects on SICI and LICI or CSP suggest gamma-aminobutyric acid (GABA)B-receptor activation. They are markedly distinct from those induced by gabapentin, although both PGB and gabapentin are thought to mediate their function by binding to the alpha2-delta subunit of voltage-gated calcium channels. Conversely, the TMS profile of PGB shows striking similarities with the pattern evoked by the GABA-reuptake inhibitor tiagabine.

Pregabalin-associated acute psychosis and epileptiform EEG-changes

Pregabalin is a novel anticonvulsive and analgesic drug that has been marketed in Europe for more than a year. The typical side effects are dizziness, somnolence and weight gain. We present a patient who, after unintended rapid up-titration of pregabalin, experienced psychotic symptoms associated with rhythmic EEG-changes resolving completely after discontinuation of pregabalin and benzodiazepine administration.

Retrospective evaluation of tiagabine overdose

BACKGROUND

Tiagabine is an anticonvulsant that blocks reuptake of the inhibitory neurotransmitter GABA. There are no published studies or case series of tiagabine overdoses.

METHODS

The records of six poison centers and one statewide poison center network were searched for all exposures to tiagabine for the years 2000-2002. Inclusion criterion was a human tiagabine exposure with follow-up to a known outcome; exclusion criterion was multiple drug ingestion.

RESULTS

57 cases met the inclusion criterion. Thirty-seven patients were female (67%). Mean and median ages were 30.5 years (S.D. +/- 18.5) and 31 years, respectively, with a range of 2 to 80 years. Seven patients were < or = 6 years. Neurologic symptoms were common: lethargy, seizures (multiple), status epilepticus, seizure (single), coma, confusion, agitation, tremors, dizziness, dystonias/abnormal posturing, and hallucinations. Other symptoms included respiratory depression, tachycardia, hypertension, and hypotension. Therapies included benzodiazepines, mechanical ventilation, phenytoin, phenobarbital, diphenhydramine, and dopamine. The mean onset and duration of symptoms were 1.3 hours (+/- 0.5, range 1-2 hours) and 9.1 hours (+/- 3.8, range 4-24 hours), respectively. Dose ingested by history was known for 38 patients (67%). The lowest dose with the development of multiple seizures and coma was 96 mg. This occurred in a 36-year-old female with a history of epilepsy. The lowest dose with symptoms in a child was 8 mg, in a 6-year-old with drowsiness. Mean dose of those with and without symptoms was 102 mg and 10 mg, respectively. The mean dose for patients experiencing seizures was 224 mg (+/- 172, range 96 to 680 mg). The mean dose for patients experiencing coma and respiratory depression was 270 mg (+/- 204, range 96 to 680 mg). Fifty-two patients (91%) were evaluated in the ED of whom 43 were admitted for medical care.

CONCLUSION

Seizures and altered mental status were common with tiagabine overdose, with rapid onset and resolution of symptoms. In this series, seizures did not occur until the ingestion was greater than three times the maximum recommended daily dose.

Status Epilepticus and Tiagabine Therapy Revisited

PURPOSE

To determine whether antiepileptic treatment with tiagabine (TGB) is associated with an increased frequency of nonconvulsive status epilepticus (NCSE) in patients with refractory epilepsy.

METHODS

We reviewed retrospectively the medical and EEG records of all inpatients with refractory localization-related epilepsy at the National Society for Epilepsy treated with TGB between January 1997 and December 2000. Clinical and electroencephalographic (EEG) data before, during, and after TGB therapy were evaluated in those patients who experienced a deterioration in seizure control suggestive of NCSE. Frequency of NCSE was determined in a comparable, non-TGB-treated patient population.

RESULTS

Seven (7.8%) of 90 TGB-treated patients were identified who experienced episodes of electroclinically confirmed NCSE. Serial EEGs showed deterioration during TGB treatment, with resolution of abnormality on discontinuation of TGB in all seven patients. During the same observation period, 32 (2.7%) of 1,165 non-TGB-treated patients developed electroclinically defined NCSE.

CONCLUSIONS

Treatment with TGB is associated with an increased frequency of NCSE in patients with refractory localization-related epilepsy.

Tiagabine-induced generalised non convulsive status epilepticus in patients with lesional focal epilepsy

PURPOSE

To report 3 cases with focal lesional epilepsy that had non-convulsive status epilepticus (NCSE) induced by treatment with tiagabine (TGB) and review the previously published cases. Drugs that enhance GABAnergic transmission are recognised to promote absence seizures in patients with generalised epilepsy syndromes and may on occasions even induce NCSE. However, that TGB can also induce NCSE in focal lesional epilepsy is not widely recognised in clinical practice.

METHOD

The clinical history, EEG and MRI findings were reviewed in 3 patients with lesional focal epilepsy who presented to our epilepsy programs over a 12 month period with TGB-induced NCSE. All previously reported cases in the English medical literature were reviewed.

RESULTS

The three patients had longstanding complex partial and secondarily generalised seizures refractory to multiple different anti-epileptic drugs. In two cases, MRI demonstrated a focal malformation of cortical development in the left parieto-occipital region and in the third left mesial temporal sclerosis. Following commencement of TGB in one patient and dose escalation in two, prolonged episodes of confusion and poor responsiveness were noted. Prolonged EEG monitoring demonstrated continuous high amplitude, generalised, 2-4 Hz delta activity with intermingled spikes during the episodes of unresponsiveness, consistent with NCSE. The clinical and EEG activity normalised following the administration of IV clonazepam followed by dose reduction or withdrawal of the TGB. Eleven previously reported cases of patients with partial epilepsy and a focal underlying lesion on MRI were identified, all of whom had similar features to that seen in our cases.

CONCLUSIONS

These cases illustrate that TGB may induce generalised NCSE in patients with focal lesional epilepsy, in addition to those with generalised syndromes. We hypothesise that patients may have developed an acquired alteration in the sensitivity of their thalamocortical circuitry that renders them more sensitive to the effects of drugs that enhance GABAnergic activity.

Management of seizures in critically ill patients

For many neurologists, seizures in critically ill patients represent a difficult problem. Etiology can be elusive because of the complexity of the environment, and treatment decisions can be compromised by the paucity of evidence-based guidelines. Emerging data support a higher than previously thought incidence of nonconvulsive epileptic activity in this patient population, which is another important consideration. Although a seizure in the intensive care unit should be treated aggressively, prophylactic antiepileptic drug administration is dependent on the specific etiology, time of onset, and ensuing complications. After ischemic stroke, prophylactic treatment is not generally recommended, and after intracerebral hemorrhage treatment is recommended only after a few weeks. After subarachnoid hemorrhage, prophylactic treatment beyond discharge is also not recommended. Although there is no reason to believe that late seizures after severe head trauma cannot be prevented with prophylactic treatment, such an approach may be useful during the first week after the injury. Physicians, however, have to individualize the treatment to the critical patient after stroke or trauma based on the presence of additional factors that increase the risk for seizures, including structural cortical injuries and medications used in critical illness with epileptogenic potential. A general therapeutic scheme for seizures in the intensive care unit and the role newer antiepileptic drugs can play are also presented in this review.

Inhibition of gamma-aminobutyric acid uptake: anatomy, physiology and effects against epileptic seizures

The transport of gamma-aminobutyric (GABA) limits the overspill from the synaptic cleft and serves to maintain a constant extracellular level of GABA. Two transporters, GABA transporter-1 (GAT-1) and GAT-3, are the most likely candidates for regulating GABA transport in the brain. Drugs acting either selectively or nonselectively at GATs exert distinct anticonvulsant effects, presumably because of distinct regions of action. Here I shall give a brief review of the localization and physiology of GATs and describe effects of selective and nonselective inhibitors thereof in different animal models of epilepsy.

Non-convulsive status epilepticus associated with tiagabine therapy in children

A case of a 7-year-old male with epilepsy who developed non-convulsive status epilepticus (NCSE) with electroclinical features consistent with those of atypical absence seizures after adjunctive antiepileptic therapy of tiagabine (TGB) is reported. The patient had frequent generalised and rare partial seizures with generalised epileptic discharges on prior electroencephalogram (EEG) recordings. NCSE was developed when rapid dosage increase and high dose of TGB was given. This case emphasises the need for close monitoring of children with epilepsy taking TGB for exacerbation of seizures or development of NCSE.

Non-convulsive status epilepticus associated with tiagabine in a pediatric patient

We report a 4-year-old patient who developed non-convulsive status epilepticus (NCSE) following tiagabine (TGB) as add-on treatment for refractory partial seizures. NCSE occurred while the patient received TGB 0.83 mg/kg/day. In our case, the TGB reduction led to a significant improvement of electroclinical features. The mechanisms of this abnormal effect are not clear. GABA-ergic hyperfunction and/or multiplicity of interlinked brain GABA systems associated with individual specific sensitivity could play a critical role in the pathogenesis of NCSE. This is the first report of NCSE documented by electroencephalogram (EEG) in a child under 12 years of age on TGB treatment.

Clinical and EEG findings in six patients with altered mental status receiving tiagabine therapy

Tiagabine (TGB), a novel GABA reuptake inhibitor antiepileptic drug, has been reported to induce nonconvulsive status epilepticus (NCSE) in patients with generalized or partial onset seizures. We describe six patients with refractory partial epilepsy treated with add-on TGB. They developed acute intermittent or progressive chronic confusion associated with diffuse slowing of the electroencephalogram (EEG), shortly after an increase in dose of TGB. This remitted in each situation after reduction of the daily dose. The possibility of nonconvulsive status epilepticus or toxic encephalopathy is discussed.