Adjunctive treatment of partial seizures with tiagabine: a placebo-controlled trial

Efficacy and safety of add-on antiseizure medications for focal epilepsy: A network meta-analysis

OBJECTIVE

Several antiseizure medications (ASMs) have been approved for the treatment of focal epilepsy. However, there is a paucity of evidence on direct comparison of ASMs. We evaluated the comparative efficacy and safety of all approved add-on ASMs for the treatment of focal epilepsy using network meta-analysis.

METHODS

Data through extensive literature search was retrieved from PubMed, Embase, Cochrane, and ClinicalTrial.gov databases using predefined search terms from inception through March 2023. PRISMA reporting guidelines (CRD42023403450) were followed in this study. Efficacy outcomes assessed were ≥50%, ≥75%, and 100% responder rates. Patient retention rate and safety outcomes such as overall treatment-emergent adverse events (TEAEs) and individual TEAEs were assessed. "Gemtc" 4.0.4 package was used to perform Bayesian analysis. Outcomes are reported as relative risks (RRs) and 95% confidence interval (CI).

RESULTS

Literature search retrieved 5807 studies of which, 75 studies were included in the analysis. All ASMs showed significantly higher ≥50% responder rate compared with placebo. Except the ≥75% seizure frequency reduction for zonisamide (2.23; 95% CI: 1.00-5.70) and 100% for rufinamide (2.03; 95% CI: 0.54-11.00), all other interventions showed significantly higher ≥75% and 100% responder rates compared with placebo. Among treatments, significantly higher 100% responder rate was observed with cenobamate compared to eslicarbazepine (10.71; 95% CI: 1.56-323.9) and zonisamide (10.63; 95% CI: 1.37-261.2). All ASMs showed a lower patient retention rate compared to placebo, with the least significant value observed for oxcarbazepine (0.77; 95% CI: 0.7-0.84). Levetiracetam showed a lower risk of incidence (1.0; 95%CI: 0.94-1.1; SUCRA: 0.885067) for overall TEAE compared with other medications.

SIGNIFICANCE

All approved ASMs were effective as add-on treatment for focal epilepsy. Of the ASMs included, cenobamate had the greatest likelihood of allowing patients to attain seizure freedom.

PLAIN LANGUAGE SUMMARY

This article compares the efficacy and safety of antiseizure medications (ASMs) currently available to neurologists in the treatment of epileptic patients. Several newer generation ASMs that have been developed may be as effective or better than the older medications. We included 75 studies in the analysis. In comparison, all drugs improved ≥50%, ≥75% and 100% responder rates compared to control, except for Zonisamide and Rufinamide in the ≥75% and 100% responder rate categories. Retention of patients undergoing treatment was lower in drugs than placebo. All drugs were tolerated, the levetiracetam showed the best tolerability. Cenobamate more likely help completely to reduce seizures.

Established and emerging GABAA receptor pharmacotherapy for epilepsy

Drugs that modulate the GABAA receptor are widely used in clinical practice for both the long-term management of epilepsy and emergency seizure control. In addition to older medications that have well-defined roles for the treatment of epilepsy, recent discoveries into the structure and function of the GABAA receptor have led to the development of newer compounds designed to maximise therapeutic benefit whilst minimising adverse effects, and whose position within the epilepsy pharmacologic armamentarium is still emerging. Drugs that modulate the GABAA receptor will remain a cornerstone of epilepsy management for the foreseeable future and, in this article, we provide an overview of the mechanisms and clinical efficacy of both established and emerging pharmacotherapies.

Research Status, Synthesis and Clinical Application of Antiepileptic Drugs

According to the 2017 ILAE's official definition, epilepsy is a slow brain disease state characterized by recurrent episodes. Due to information released by ILAE in 2017, it can be divided into four types, including focal epilepsy, generalized epilepsy, combined generalized, and focal epilepsy, and unknown epilepsy. Since 1989, 24 new antiepileptic drugs have been approved to treat different types of epilepsy. Besides, there are a variety of antiepileptic medications under clinical monitoring. These novel antiepileptic drugs have plenty of advantages. Over the past 33 years, there have been many antiepileptic drugs on the mearket, but no one has been found that can completely cure epilepsy. In this paper, the mentioned drugs were classified according to their targets, and the essential information, and clinical studies of each drug were described. The structure-activity relationship of different chemical structures was summarized. This paper provides help for the follow-up research on epilepsy drugs.

Anti-seizure medications and efficacy against focal to bilateral tonic-clonic seizures: A systematic review with relevance for SUDEP prevention

We conducted a systematic review of anti-seizure medications (ASMs) and their efficacy for the control of focal to bilateral tonic-clonic seizures (FBTCS). FBTCS, especially when nocturnal, are recognized as one of the major risk factors for Sudden Unexpected Death in Epilepsy (SUDEP). We searched different online databases for all the randomized, double-blinded, and placebo-controlled clinical trials of ASMs that were FDA-approved after 1990 and that reported specifically on the reduction in FBTCS; when possible, this was compared to reduction in focal impaired awareness (FIA) seizures. The ASMs that yielded the most data (3 or more studies) were topiramate (TPM), followed by tiagabine (TGB), brivaracetam (BRV), and lamotrigine (LTG). TPM trials showed a reduction in FBTCS of 44.8% to 100% (4.5-99% over placebo); TGB 21.8% to 46.7% (21.8-61% over placebo); BRV 33.9% to 82.1% (11.6-57.4% over placebo); and LTG 55.2% (20.3-52% over placebo). Promising results, but with data from only one or two studies, were seen with cenobamate (18-59% efficacy above placebo), lacosamide (45.1-78.7%), levetiracetam (40.1-60.3%), oxcarbazepine (58.5-81.5%), and gabapentin (50-53.8%). Higher responses were often seen at higher doses, including at doses above those currently approved by the FDA. Results specific to nocturnal FBTCS were never reported for any ASM. Moreover, complete freedom from FBTCS specifically was very rarely reported, despite its relevance for SUDEP prevention. In conclusion, there are few data specifically comparing the efficacy of ASMs for prevention of FBTCS despite the known strong association of BTCS with SUDEP. This review was our attempt at filling a gap in the literature and calling for universal reporting of data specific to BTC seizure reduction in all future studies, preferably including specific reporting on nocturnal BTCS. This will help enable rational ASM selection to minimize BTC seizures and thereby decrease the risk of SUDEP.

Tiagabine add-on therapy for drug-resistant focal epilepsy

BACKGROUND

Epilepsy is a common neurological condition that affects up to 1% of the population. Nearly 30% of people with epilepsy are resistant to currently available antiepileptic drugs (AEDs) and require treatment with multiple antiepileptic drugs in combination. Tiagabine is one of the newer AEDs that can be used as an adjunct (add-on) to standard AEDs.

OBJECTIVES

To evaluate the efficacy and tolerability of tiagabine when used as an add-on treatment for people with drug-resistant focal seizures.

SEARCH METHODS

This is an updated Cochrane review, last published in 2014. For the latest update, we searched the following databases on 22 January 2019: Cochrane Register of Studies (CRS Web), which includes the Cochrane Epilepsy Group's Specialized Register and the Cochrane Central Register of Controlled Trials, MEDLINE (Ovid, 1946 to January 21, 2019), ClinicalTrials.gov, and the WHO International Clinical Trials Registry Platform. We imposed no language restrictions. We also contacted the manufacturers of tiagabine and experts in the field to identify any ongoing or unpublished studies.

SELECTION CRITERIA

We included randomised placebo-controlled add-on trials conducted in people of any age with focal epilepsy. The studies could be double-, single-, or unblinded and of parallel or cross-over design. They had to have a minimum treatment period of eight weeks. We also included trials using an active drug control group.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trials for inclusion and extracted data according to the standard methodological procedures expected by the Cochrane Collaboration for this review update. We resolved disagreements by discussion. Outcomes investigated included 50% or greater reduction in seizure frequency, treatment withdrawal, adverse effects, effects on cognition and quality of life. The primary analyses were performed by intention-to-treat. We calculated worst-case and best-case analyses for seizure outcomes. We evaluated dose response using regression models. Two review authors assessed risk of bias in each study using the Cochrane 'Risk of bias' tool.

MAIN RESULTS

No further studies were added since the previous update in 2014. The review included six trials (four parallel-group and two cross-over group trials) consisting of 948 participants. For the main comparison, tiagabine versus placebo, all participants were aged between 12 and 77 years and the study treatment periods ranged from 12 to 22 weeks. The overall risk ratio (RR) with 95% confidence intervals (CIs) for a 50% or greater reduction in seizure frequency (tiagabine versus placebo) was 3.16 (95% CI 1.97 to 5.07; 3 trials; 769 participants; high-certainty evidence). Because of differences in response rates among trials, regression models were unable to provide reliable estimates of response to individual doses. The RR for treatment withdrawal (tiagabine versus placebo) was 1.81 (95% CI 1.25 to 2.62; 3 trials, 769 participants; moderate-certainty evidence). Dizziness and tremor were significantly associated with tiagabine therapy. For cognitive and quality-of-life outcomes, the limited available data suggested no significant effects on cognition, mood, or adjustment. One trial comparing tiagabine with an active drug control group (tiagabine versus topiramate) found no significant differences between the two add-on drugs for a 50% or greater reduction in seizure frequency (RR 0.54, 95% CI 0.19 to 1.58; 1 trial; 41 participants) or for treatment withdrawal (RR 1.43, 95% CI 0.74 to 2.74; one trial; 41 participants). We judged two of the six included studies to have low risk of bias, three studies to have an unclear risk of bias, and one study to have a high risk of bias. Methods for randomisation sequence generation were the least reported trial design factor and generated the most concerns regarding risk of bias. We rated the overall certainty of the evidence as largely moderate to high using the GRADE approach. We rated the evidence for two of the adverse effect outcomes, nausea and tremor, as low certainty.

AUTHORS' CONCLUSIONS

Tiagabine reduced seizure frequency but was associated with some adverse effects when used as an add-on treatment in people with drug-resistant focal epilepsy. The findings of the current review are mainly applicable to adults and adolescents, and may not necessarily be applicable to children as none of the trials included participants aged under 12 years. We found no significant differences between tiagabine and topiramate as add-on drugs; however, evidence was provided by a single trial and was therefore limited.

Comparative effectiveness of add-on therapy with newer-generation antiepileptic drugs in Bulgarian patients with refractory epilepsy

OBJECTIVES

The objective of this study is to perform an open, prospective study on various aspects of comparative effectiveness of newer-generation antiepileptic drugs as add-on therapy in Bulgarian patients with drug-resistant epilepsy.

METHODS

The study was performed with the participation of 1259 patients with epilepsy who attended the Clinic of Neurology at the University Hospital in Plovdiv, Bulgaria for regular visits and completed diaries about seizure frequency, severity, and adverse events.

RESULTS

Oxcarbazepine was used in 82 patients, topiramate in 120 patients, lamotrigine in 73 patients, levetiracetam in 135 patients, pregabalin in 47 patients, tiagabine in 43 patients, gabapentin in 18 patients, lacosamide in 12 patients, and retigabine in 6 patients. During the first 24 months of study, improvement of seizure severity and frequency was most frequent in patients on treatment with pregabalin and levetiracetam and rarest in those on treatment with oxcarbazepine. The retention rate of patients on pregabalin and tiagabine was significantly lower compared to the retention rate of patients on most of the other antiepileptic drugs. The frequency of adverse events was higher in patients on treatment with tiagabine and pregabalin.

CONCLUSION

Despite some similar characteristics of newer-generation antiepileptic drugs' effectiveness, levetiracetam stands out with better dynamic improvement of seizure severity and frequency and satisfactory tolerability; typical for pregabalin is a very good dynamic improvement of seizure severity and frequency mainly in patients with focal seizures, but a lower tolerability, and the main advantage of oxcarbazepine is a good tolerability, efficacy, however, is less satisfactory.

New generation antiepileptic drugs: what do they offer in terms of improved tolerability and safety?

Over the last two decades a total of 11 antiepileptic drugs (AEDs) have been introduced to the US market. Randomized, placebo-controlled trials have yielded information about each drug's efficacy, tolerability, and safety profile; however, few studies have compared the newer generation AEDs directly with the older generation. Comparative studies are not always straightforward in their interpretation, as many characteristics of drugs, both favorable and unfavorable, may not be highlighted by such studies. In general, findings from the literature suggest that the newer generation AEDs (including vigabatrin, felbamate, gabapentin, lamotrigine, tiagabine, topiramate, levetiracetam, oxcarbazepine, zonisamide, pregabalin, rufinamide, and lacosamide) enjoy both improved tolerability and safety compared with older agents such as phenobarbital, phenytoin, carbamazepine, and valproate. This is partially supported by some of the findings of the QSS and the TTA Committee of the American Academy of Neurology (AAN), whose review of four AEDs (gabapentin, lamotrigine, topiramate, and tiagabine) is discussed. Briefly, when compared with carbamazepine, lamotrigine was better tolerated; topiramate adverse events (AEs) were fairly comparable to carbamazepine and valproate; and tiagabine compared with placebo was associated with a higher discontinuation rate due to AEs. The findings of the SANAD trial are also presented; when administered to patients with partial epilepsy, carbamazepine was most likely to fail due to AEs, and lamotrigine and gabapentin were least likely to fail due to AEs. When administered to patients with idiopathic generalized epilepsy, topiramate was most frequently associated with AE-related discontinuation, followed by valproate; and while valproate was the most efficacious drug in this arm of the study, lamotrigine was more tolerable. What makes the SANAD study valuable and somewhat unique is its head-to-head comparison of one drug with another. Such comparative trials are overall lacking for new AEDs, although some conclusions can be drawn from the available data. In the end, however, AED selection must be based on individual patient and drug characteristics.

Tiagabine add-on for drug-resistant partial epilepsy

BACKGROUND

Epilepsy is a common neurological condition that affects almost 0.5% to 1% of the population. Nearly 30% of people with epilepsy are resistant to currently available drugs. Tiagabine is one of the newer antiepileptic drugs; its effects as an adjunct (add-on) to standard drugs are assessed in this review.

OBJECTIVES

To evaluate the effects of add-on treatment with tiagabine on seizures, adverse effects, cognition and quality of life for people with drug-resistant localisation-related seizures.

SEARCH METHODS

This is an updated version of the original Cochrane review published in 2012 (Issue 5). We searched the Cochrane Epilepsy Group Specialised Register (November 2013), the Cochrane Central Register of Controlled Trials (CENTRAL, 2013, Issue 10) and MEDLINE (1946 to November 2013). No language restrictions were imposed. We also contacted the manufacturers of tiagabine and experts in the field to seek any ongoing or unpublished studies.

SELECTION CRITERIA

Randomised placebo-controlled add-on trials of people of any age with localisation-related seizures in which an adequate method of concealment of randomisation was used were included. The studies could be double-blind, single-blind or unblinded and of parallel or cross-over design. They had to have a minimum treatment period of eight weeks. Trials using an active drug control group were also included.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials for inclusion and extracted data. Disagreements were resolved by discussion. Outcomes investigated included 50% or greater reduction in seizure frequency, treatment withdrawal, adverse effects, effects on cognition and quality of life. The primary analyses were performed by intention-to-treat. Worst-case and best-case analyses were calculated for seizure outcomes. Dose response was evaluated in regression models. Risk of bias in each study was assessed by two review authors using the Cochrane 'Risk of bias' tool.

MAIN RESULTS

Four parallel-group and two cross-over group trials were included. The overall risk ratio (RR) with 95% confidence intervals (CIs) for a 50% or greater reduction in seizure frequency (tiagabine vs placebo) was 3.16 (95% CI 1.97 to 5.07). Because of differences in response rates among trials, regression models were unable to provide reliable estimates of response to individual doses. The RR for treatment withdrawal was 1.81 (95% CI 1.25 to 2.62). The 99% CIs for the adverse effects of dizziness, fatigue, nervousness and tremor did not include unity, indicating that they are significantly associated with tiagabine. For cognitive and quality of life outcomes, the limited available data suggested no significant effects on cognition and mood and adjustment. Two of the five studies were judged as having low risk of bias, three studies unclear risk of bias and one study high risk of bias. Overall study quality was rated as high using the GRADE approach.

AUTHORS' CONCLUSIONS

Tiagabine reduces seizure frequency but is associated with some adverse effects when used as an add-on treatment for people with drug-resistant localisation-related seizures.

A revisited strategy for antiepileptic drug development in children: designing an initial exploratory step

BACKGROUND

Randomized controlled trials (RCTs) in refractory paediatric epilepsy usually involve the two main types of epilepsy shared by children and adults, focal epilepsy and Lennox-Gastaut syndrome (LGS). Most other epilepsy syndromes, specifically paediatric, are excluded from drug development. In order to identify among them the candidate(s) for dedicated RCTs with a new drug, the European Medicine Agency (EMA) recently recommended proceeding in two steps: (1) an exploratory (prospective-observational) trial (POT) including a large variety of paediatric epilepsy syndromes and (2) a subsequent RCT in each of those that disclose a signal for possible efficacy.

OBJECTIVE

Our objective was to address the three following issues that have not been addressed by the EMA: (1) to determine a minimal threshold for this signal; (2) to establish a list of epilepsies to evaluate; and (3) to estimate the number of patients to include in such POTs.

METHODS

We extensively reviewed the POTs (including various syndromes) and RCTs reported in paediatric patients with uncontrolled epilepsy using MEDLINE (from 1990 to 2011) and the Cochrane library. We determined the threshold as the lowest percentage of responders observed in a POT with a positive corresponding RCT. The syndromes that reached this threshold in a POT were those to evaluate in an RCT. The minimal number of patients to include for each syndrome for a POT with a new antiepileptic drug was estimated in order to reach at least this threshold of responders with a 95 % confidence interval.

RESULTS

We found the minimal responder threshold to be 25 %. We identified eight epilepsy types/syndromes reaching this threshold and estimated for each of them the minimal sample needed: refractory focal epilepsy (n = 40), Lennox-Gastaut syndrome (n = 32), infantile spasms (n = 50), Dravet syndrome (n = 32), childhood absence epilepsy (n = 12), other symptomatic generalized epilepsy (n = 38), epileptic encephalopathy with continuous spikes and waves during sleep (n = 7) and epilepsy with myoclonic-astatic seizures (n = 4) [the two last samples may be underestimated due to the lack of RCTs in these conditions].

CONCLUSION

Among the eight epilepsy types/syndromes that we recommend to systematically include in exploratory trials using the POT procedure, we assume that, for the minimal sample given above, a responder threshold of 25 % will provide a reliable efficacy signal, to be confirmed by a dedicated RCT. This strategy should avoid missing new therapeutic possibilities for children with epilepsy and reduce the off-label use of drugs in paediatric neurology.

Tiagabine add-on for drug-resistant partial epilepsy

BACKGROUND

Epilepsy is a common neurological condition, affecting almost 0.5 to 1% of the population. Nearly 30% of people with epilepsy are resistant to currently available drugs. Tiagabine is one of the newer antiepileptic drugs and its effects as an adjunct (add-on) to standard drugs are assessed in this review.

OBJECTIVES

To evaluate the effects of add-on treatment with tiagabine upon seizures, adverse effects, cognition and quality of life for people with drug-resistant localisation related seizures.

SEARCH METHODS

This is an updated version of the original Cochrane review published in issue 10, 2010. We searched the Cochrane Epilepsy Group's Specialised Register (December 2011), the Cochrane Central Register of Controlled Trials (CENTRAL, issue 4, 2011 of The Cochrane Library), and MEDLINE (1948 to November 2011). No language restrictions were imposed. We also contacted the manufacturers of tiagabine and experts in the field to seek any ongoing or unpublished studies.

SELECTION CRITERIA

Randomised placebo controlled add-on trials of people of any age with localisation related seizures, in which an adequate method of concealment of randomisation was used were included. The studies could be double, single or unblinded and be of parallel or crossover design. They had to have a minimum treatment period of eight weeks. Trials using an active drug control group were also included.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials for inclusion and extracted data. Any disagreements were resolved by discussion. Outcomes investigated included 50% or greater reduction in seizure frequency; treatment withdrawal; adverse effects; effects on cognition and quality of life. The primary analyses were by intention-to-treat. Worst case and best case analyses were also calculated for seizure outcomes. Dose response was evaluated in regression models.

MAIN RESULTS

Four parallel group and two crossover group trials were included. The overall relative risk (RR) with 95% confidence intervals (CIs) for a 50% or greater reduction in seizure frequency (tiagabine versus placebo) was 3.16 (95% CI 1.97 to 5.07). Due to differences in response rates among trials, regression models were unable to provide reliable estimates of responses to individual doses. The RR for treatment withdrawal was 1.81 (95% CI 1.25 to 2.62). The 99% CIs for the following adverse effects: dizziness; fatigue; nervousness and tremor did not include unity, indicating that they are significantly associated with tiagabine. For cognitive and quality of life outcomes the limited data available suggested that there were no significant effects on cognition and mood and adjustment.

AUTHORS' CONCLUSIONS

Tiagabine reduces seizure frequency but is associated with some adverse effects when used as an add-on for people with drug-resistant localisation-related seizures.

Drug treatment of epilepsy in the century of the ILAE: the second 50 years, 1959-2009

The drug therapy of epilepsy evolved enormously in this 50 year period. Advances in therapeutics included the incorporation of pharmacokinetics into clinical practice, enormous advances in neurochemistry, a trend to antiepileptic drug monotherapy, better drug assessment, better understanding of therapeutic outcomes, and the recognition of the large epilepsy treatment gap in many countries. An unprecedented range of new drugs was introduced in this period. Before 1989, these included carbamazepine, valproate, ethosuximide, and the benzodiazepines. Since 1989, 13 more new drugs have been licensed and marketed and there are others in the pipeline. The International League Against Epilepsy and its leading figures have played an important role in these developments. In this period, too, there has been a rapid expansion in research and development within the pharmaceutical industry and a rise in the value of the antiepileptic drug market. In parallel, governmental regulation of pharmaceuticals has greatly increased. To what extent the overall prognosis of epilepsy has improved as a result of these activities is an interesting and perplexing question.

Advancements in the Treatment of Epilepsy

Diagnostic tools and treatment options for epilepsy have expanded in recent years. Imaging techniques once confined to research laboratories are now routinely used for clinical purposes. Medications that were unavailable a few years ago are now first-line agents. Patients with refractory seizures push for earlier surgical intervention, consider treatment with medical devices, and actively seek nonpharmacologic alternatives. We review some of these recent advances in the management of epilepsy.

Second-generation antiepileptic drugs' impact on balance: a meta-analysis

OBJECTIVE

To systematically review available evidence regarding whether second-generation antiepileptic drugs (AEDs) contribute to the risk of balance disorders.

METHODS

We systematically evaluated data from randomized controlled trials that compared adjunctive therapy with a second-generation AED (gabapentin, lamotrigine, levetiracetam, oxcarbazepine, pregabalin, tiagabine, topIramate, or zonisamide) vs placebo for partial epilepsy and that reported dose-specific rates of ataxia or Imbalance for each group. Random-effects meta-analysis was used to pool ratios (risk ratio [RR]) and associated 95% confidence Intervals to determine whether there was evidence of an overall AED class effect or a dose-response effect and whether there were differences between Individual AEDs.

RESULTS

Sixteen studies met inclusion criteria, representing 4279 individuals randomized to a second-generation AED and 1830 patients to placebo. Pooled analyses of all AEDs demonstrated that they Increase imbalance risk at any dose (RR, 2.73; 95% confidence interval, 2.07-3.61) and at lowest dose (RR, 1.76; 95% confidence interval, 1.26-2.46). The highest dose analysis showed heterogeneity; evaluation of individual AEDs revealed that oxcarbamazepine and topiramate increased imbalance risk at all doses, whereas gabapentin and levetiracetam did not increase imbalance risk at any dose. A dose-response effect was observed for most AEDs.

CONCLUSION

Second-generation AEDs at standard dosages, except for gabapentin and levetiracetam, increase the imbalance risk, and evidence exists for a dose-response effect. The mechanisms, risk factors, and consequences of this risk for individual AEDs warrant further study.

Negative Effects of Antiepileptic Drugs on Mood in Patients with Epilepsy

With the introduction of several new antiepileptic drugs into clinical practice, renewed attention has been focussed on treatment-emergent adverse effects, including mood disorders. There are several possible causes of psychiatric disorders in patients with epilepsy, including antiepileptic drugs, and it is often difficult to determine whether psychopathological manifestations, especially depressive symptoms, are due to drug therapy or to multiple other factors. Assessment of the negative effects of antiepileptic drugs on mood should always consider all potential factors. Case series, audits and open observational studies can identify psychopathological features, case-control studies are useful for identifying the endophenotypes of patients at risk of adverse effects on mood, and controlled clinical trials give good estimates of incidence of such effects, adjusted for the spontaneous occurrence of symptoms. The barbiturates, vigabatrin and topiramate show greater associations with the occurrence of depressive symptoms than other antiepileptic drugs, presenting in up to 10% of all patients, but even more so in susceptible patients. Data on zonisamide are scarce but it seems that mood disorders may occur in approximately 7% of patients who are receiving high dosages of this drug. In most cases, the use of monotherapy, with slow titration schedules, can significantly reduce the incidence of mood disorders. Tiagabine, levetiracetam and felbamate present an intermediate risk, with prevalence of depression of about 4% or lower. Phenytoin, ethosuximide, carbamazepine, oxcarbazepine, gabapentin, sodium valproate, pregabalin and lamotrigine are all associated with low risks for depression (<1%), and several of these antiepileptic drugs seem to have a positive effect on mood. Antiepileptic drugs can negatively affect mood and behaviour by different mechanisms: potentiation of GABA neurotransmission, folate deficiency, pharmacodynamic interactions with other antiepileptic drugs in polytherapy regimens, forced normalisation. Individuals with a personal or family history of depression should be carefully followed after initiation of therapy with a new antiepileptic drug, especially if structural brain abnormalities such as hippocampal sclerosis are present.

Comparison of the Cognitive Effects of Tiagabine and Carbamazepine as Monotherapy in Newly Diagnosed Adult Patients with Partial Epilepsy: Pooled Analysis of Two Long-term, Randomized, Follow-up Studies

PURPOSE

Patients with epilepsy are at greater risk for cognitive impairment than are age- and education-matched controls. Cognitive decline is a significant adverse event associated with many first-generation anticonvulsant drugs (AEDs); however, the past decade has seen the introduction of several new AEDs with more-favorable cognitive profiles. Tiagabine (TGB) is indicated as adjunctive therapy for the treatment of partial seizures. The cognitive effects of TGB and carbamazepine (CBZ) monotherapy were evaluated in adult epilepsy patients with partial seizures.

METHODS

This analysis pooled data from two randomized studies with similar populations, dosing, and cognitive assessments. TGB was titrated to 20-30 mg/day and CBZ to 400-800 mg/day over a 6-week period. A control or no-drug group of untreated patients with a single epileptic seizure was included for comparison. Cognitive function was assessed at baseline and 52 weeks.

RESULTS

Of the 105 epilepsy patients enrolled, 79 completed the 52 weeks of monotherapy (TGB, 74%; CBZ, 77%). Altogether, 19 untreated patients composed the no-drug group. During the 52-week follow-up, only one statistically significant difference was found between the treatment groups and the no-drug group [verbal fluency task: F(2, 92) = 3.16; p = 0.047]. On further analysis, it was determined that this statistical difference was solely based on the patients receiving CBZ performing worse than the control group (p = 0.048). Statistically significant improvements (p < 0.05) were found on six (26%) of 23 variables with TGB and CBZ, as well as the no-drug group, although the variables differed between the groups. Significant worsening in the test scores was not seen in any of the study groups.

CONCLUSIONS

The results of this 52-week, follow-up study show that successful TGB monotherapy with 20-30 mg/day has a cognitive profile similar to that of successful long-term CBZ monotherapy with 400-800 mg/day in newly diagnosed patients with epilepsy and to that of untreated patients with a single seizure. We observed no significant decline in cognitive scores associated with TGB monotherapy.

Lamotrigine for neuropathic pain

Lamotrigine is an antiepileptic drug that stabilizes neural membranes by blocking the activation of voltage-sensitive sodium channels and inhibiting the presynaptic release of glutamate. Full length reports of five open trials and six out of seven randomized controlled trials (plus two abstracts) have demonstrated the efficacy of lamotrigine in the treatment of various forms of neuropathic pain. The present drug profile provides a review of the pharmacologic properties of lamotrigine, the clinical evidence related to its efficacy and safety, and discusses the current and future role of the drug in the treatment of neuropathic pain.

Efficacy and tolerability of the new antiepileptic drugs, II: Treatment of refractory epilepsy: report of the TTA and QSS Subcommittees of the American Academy of Neurology and the American Epilepsy Society

PURPOSE

To assess the evidence demonstrating efficacy, tolerability, and safety of seven new antiepileptic drugs (AEDs) [gabapentin (GBP), lamotrigine (LTG), topiramate (TPM), tiagabine (TGB), oxcarbazepine (OXC), levetiracetam (LEV), and zonisamide (ZNS)] in the treatment of children and adults with refractory partial and generalized epilepsies.

METHODS

A 23-member committee, including general neurologists, pediatric neurologists, epileptologists, and doctors in pharmacy, evaluated the available evidence based on a structured literature review including MEDLINE, Current Contents, and Cochrane Library for relevant articles from 1987 to March 2003.

RESULTS

All of the new AEDs were found to be appropriate for adjunctive treatment of refractory partial seizures in adults. GBP can be effective for the treatment of mixed seizure disorders, and GBP, LTG, OXC, and TPM for the treatment of refractory partial seizures in children. Limited evidence suggests that LTG and TPM also are effective for adjunctive treatment of idiopathic generalized epilepsy in adults and children, as well as treatment of the Lennox-Gastaut syndrome.

CONCLUSIONS

The choice of AED depends on seizure and/or syndrome type, patient age, concomitant medications, and AED tolerability, safety, and efficacy. The results of this evidence-based assessment provide guidelines for the prescription of AEDs for patients with refractory epilepsy and identify those seizure types and syndromes for which more evidence is necessary.

Tiagabine synergistically interacts with gabapentin in the electroconvulsive threshold test in mice

Polytherapy, based on the rational combining of antiepileptic drugs (AEDs), is required for patients with drug-resistant epilepsy. In such cases, the combinations of AEDs usually offer a significant enhancement of their protective effects against seizures. There has appeared a hypothesis that combining two AEDs, influencing the same neurotransmitter system, results in the potentialization of their anticonvulsant effects. For corroborating this hypothesis, a pharmacological character of interaction between tiagabine (TGB) and gabapentin (GBP)-two novel AEDs affecting the GABA-ergic system, in the maximal electroshock seizure threshold (MEST)-test in mice was evaluated. TGB at the dose of 4 mg/kg and GBP at 75 mg/kg significantly raised the electroconvulsive threshold. Further, using the isobolographic calculations, TGB was coadministered with GBP at three fixed-ratios (1 : 3, 1 : 1, and 3 : 1) of their respective protective drug doses. All examined combinations of TGB with GBP exerted supra-additive (synergistic) interactions against MEST-induced seizures in mice. The interaction index, describing the strength and magnitude of interaction, ranged between 0.25 and 0.50 indicating supra-additivity. Adverse (neurotoxic) effects were evaluated in the chimney (motor performance) and the step-through, light-dark passive avoidance (long-term memory) tests in mice. The examined combinations of TGB with GBP did not affect the motor coordination, except for the fixed-ratio of 1 : 1, at which significant impairment of motor performance was observed. Moreover, all combinations selectively impaired the acquisition of the task in the passive avoidance test, having no impact on consolidation and retrieval in the long-term memory test. The pain threshold test revealed that the observed disturbances in the passive avoidance testing resulted presumably from the antinociceptive activity of these AEDs in combinations. After lengthening the exposing time to the direct current stimulus in the passive avoidance test from 2 to 6 s, the acquisition of the task, in animals receiving the combinations of TGB and GBP was not impaired. Neither the plasma, nor brain concentrations of GBP were affected by TGB application, so pharmacokinetic events that might negatively influence the observed effects are not probable. Results of this study clearly indicate that the activation of the same neurotransmitter system (GABA-ergic) leads to a synergistic interaction. The pain threshold test is a very good paradigm for screening the antinociceptive properties of AEDs, which may disturb the long-term memory testing in animals. Combinations of TGB with GBP (very promising from a preclinical point of view) should be clinically verified for elaborating the most effective treatment regimen in patients with intractable seizures.

Effects of 3-hydroxy-4-amino-4,5,6,7-tetrahydro-1,2-benzisoxazol (exo-THPO) and its N-substituted analogs on GABA transport in cultured neurons and astrocytes and by the four cloned mouse GABA transporters

The system of GABA transporters in neural cells constitutes an efficient mechanism for terminating inhibitory GABAergic neurotransmission. As such these transporter are important therapeutical targets in epilepsy and potentially other neurological diseases related to the GABA system. In this study a number of analogs of 3-hydroxy-4-amino-4,5,6,7-tetrahydro-1,2-benzisoxazol (exo-THPO), a promising lead structure for inhibitors of GABA uptake were investigated. It was found that the selectivity of N-acetyloxyethyl-exo-THPO for inhibition of the astroglial GABA uptake system was 10-fold as compared to inhibition of the neuronal GABA uptake system. Selectivity in this magnitude may provide potent anti-convulsant activity as has recently been demonstrated with the likewise glia-selective GABA uptake inhibitor, N-methyl-exo-THPO. In contrast to the competitive inhibition of GABA uptake exhibited by N-substituted analogs of 4,5,6,7-tetrahydroisoxazolo[4,5-c]pyridin-3-ol (THPO), nipecotic acid, and guvacine, N-4,4-diphenyl-3-butenyl(DPB)-N-methyl-exo-THPO and 4-phenylbutyl-exo-THPO exhibited non-competitive type inhibition kinetics. The lipophilic character of a number of GABA analogs was concluded by far to constitute the determining factor for the potency of these compounds as inhibitors of GAT1-mediated uptake of GABA. This finding underscores the complexity of the pharmacology of the GABA transport system, since these non-competitive inhibitors are structurally very similar to some competitive GABA uptake inhibitors. Whether these structure-activity relationships for inhibition of GABA uptake may provide sufficient information for the development of new structural leads and to what extent these compounds may be efficient as therapeutical anti-convulsant agents remain to be elucidated.

Interactions of tiagabine with some antiepileptics in the maximal electroshock in mice

Tiagabine (TGB), a new potent gamma-aminobutyric acid (GABA) uptake inhibitor, is widely applied in adjunctive treatment of partial seizures in humans. Although, polytherapy is not an initial method of epilepsy treatment, clinicians often combine TGB with other antiepileptics as add-on therapy for assuring the anticonvulsant protection in patients with refractory seizures. To evaluate the character of pharmacological interactions between TGB and some antiepileptics, the isobolographic analysis was used as a suitable method for determining the exact types of interactions. Determination of an influence of TGB on the protective effects of diphenylhydantoin (DPH), carbamazepine (CBZ), valproate (VPA), phenobarbital (PB), lamotrigine (LTG), topiramate (TPM), and felbamate (FBM) in maximal electroshock-induced seizures was essential for this study. To exclude or confirm a pharmacokinetic character of observed interactions, the free plasma and brain concentrations of antiepileptic drugs (AEDs) studied were evaluated by using the immunofluorescence or high-pressure liquid chromatography (HPLC).TGB (up to 2.5 mg/kg) remained ineffective upon the electroconvulsive threshold, whilst the drug in doses of 5 and 10 mg/kg significantly raised the electroconvulsive threshold in mice. According to the isobolography, TGB appears to act synergistically with VPA. The remaining combinations tested exerted additive interactions. A pharmacokinetic character of interaction between TGB and VPA was evidently corroborated either in plasma or brains. Moreover, TGB significantly reduced the plasma and brain concentrations of DPH; however, pharmacokinetic events were not accompanied by any changes in anticonvulsant activity of the latter. Finally, the isobolographic analysis revealed that combinations of TGB with VPA exerted synergistic (supra-additive) interaction resulting from a pharmacokinetic interaction.

Therapeutics in pediatric epilepsy, Part 1: The new antiepileptic drugs and the ketogenic diet

Epilepsy is one of the most common and challenging neurologic disorders affecting children. Although various modalities exist to treat pediatric-onset seizures, seizures in 25% of children who are diagnosed as having epilepsy remain refractory to available therapies. Of the 8 new antiepileptic drugs (AEDs) (felbamate, gabapentin, lamotrigine, topiramate, tiagabine, levetiracetam, oxcarbazepine, and zonisamide), all but 2 (zonisamide and levetiracetam) have received Food and Drug Administration approval for adjunctive use in the pediatric population. However, most of the new AEDs used in adults have also been used in children, beyond the AEDs' approved indications. The ultimate goal of patient management is to choose the therapeutic option that provides the best chance of improving the patient's quality of life. Issues that relate to treatment choice include the likelihood of seizure recurrence, type and severity of seizures, available AED efficacies and toxicities, need for hematologic monitoring, ease of dosing, underlying medical conditions, medication interactions, urgency of initiating therapy, and cost. In this review, we discuss these issues for each of the 8 new AEDs; we also discuss the ketogenic diet and briefly review the older AEDs. Knowledge of the available AEDs will enable the practitioner to choose the best drug or drugs for individual patients.

Tiagabine add-on for drug-resistant partial epilepsy

BACKGROUND

Epilepsy is a common neurological condition, affecting almost 0.5 to 1 per cent of the population. Nearly 30 per cent of people with epilepsy are resistant to currently available drugs. Tiagabine is one of the newer antiepileptic drugs and its effects as an adjunct (add-on) to standard drugs is assessed in this review.

OBJECTIVES

To evaluate the effects of add-on treatment with tiagabine upon seizures, side effects, cognition and quality of life for people with drug-resistant localization related seizures.

SEARCH STRATEGY

We searched the Cochrane Epilepsy Group trials register (28 March 2002), the Cochrane Controlled Trials Register (Cochrane Library Issue 1, 2002), MEDLINE (1966 to November 2001). In addition, we contacted Sanofi~Synthelabo (makers of tiagabine) and experts in the field to seek any unpublished or ongoing studies.

SELECTION CRITERIA

Randomized placebo controlled add-on trials of people of any age with localization related seizures, in which an adequate method of concealment of randomization was used. The studies could be double, single or unblinded and be of parallel or crossover design. They had to have a minimum treatment period of eight weeks.

DATA COLLECTION AND ANALYSIS

Two reviewers independently selected trials for inclusion and extracted data. Any disagreements were resolved by discussion. Outcomes investigated included 50 per cent or greater reduction in seizure frequency; treatment withdrawal; side effects; effects on cognition and quality of life. The primary analyses were by intention-to-treat. Worst case and best case analyses were also calculated for seizure outcomes. Dose response was evaluated in regression models.

MAIN RESULTS

Three parallel group and two crossover group trials were included. The overall relative risk (RR) for a 50 per cent or greater reduction in seizure frequency (tiagabine versus placebo) was 3.16(95% confidence interval 1.97 to 5.07). Due to differences in response rates among trials, regression models were unable to provide reliable estimates of responses to individual doses. The RR for treatment withdrawal was 1.81(95% confidence interval 1.25 to 2.62). The 99% confidence interval for the following side effects: dizziness; fatigue; nervousness and tremor did not include unity, indicating that they are significantly associated with tiagabine. For cognitive and quality of life outcomes the limited data available suggested that there were no significant effects on cognition and mood and adjustment.

REVIEWER'S CONCLUSIONS

Tiagabine reduces seizures frequency but is associated with some side effects when used as an add-on for people with drug-resistant localization related seizures.

GABAergic mechanisms in epilepsy

gamma-Aminobutyric acid (GABA), the principal inhibitory neurotransmitter in the cerebral cortex, maintains the inhibitory tone that counterbalances neuronal excitation. When this balance is perturbed, seizures may ensue. GABA is formed within GABAergic axon terminals and released into the synapse, where it acts at one of two types of receptor: GABAA, which controls chloride entry into the cell, and GABAB, which increases potassium conductance, decreases calcium entry, and inhibits the presynaptic release of other transmitters. GABAA-receptor binding influences the early portion of the GABA-mediated inhibitory postsynaptic potential, whereas GABAB binding influences the late portion. GABA is rapidly removed by uptake into both glia and presynaptic nerve terminals and then catabolized by GABA transaminase. Experimental and clinical study evidence indicates that GABA has an important role in the mechanism and treatment of epilepsy: (a) Abnormalities of GABAergic function have been observed in genetic and acquired animal models of epilepsy; (b) Reductions of GABA-mediated inhibition, activity of glutamate decarboxylase, binding to GABAA and benzodiazepine sites, GABA in cerebrospinal fluid and brain tissue, and GABA detected during microdialysis studies have been reported in studies of human epileptic brain tissue; (c) GABA agonists suppress seizures, and GABA antagonists produce seizures; (d) Drugs that inhibit GABA synthesis cause seizures; and (e) Benzodiazepines and barbiturates work by enhancing GABA-mediated inhibition. Finally, drugs that increase synaptic GABA are potent anticonvulsants. Two recently developed antiepileptic drugs (AEDs), vigabatrin (VGB) and tiagabine (TGB), are examples of such agents. However, their mechanisms of action are quite different (VGB is an irreversible suicide inhibitor of GABA transaminase, whereas TGB blocks GABA reuptake into neurons and glia), which may account for observed differences in drug side-effect profile.

Tiagabine in clinical practice

Among the newly introduced antiepileptic drugs (AEDs), tiagabine (TGB) stands out as a compound with a well-understood and documented mechanism of action. It is a lipophilic derivative of nipecotic acid that blocks gamma-aminobutyric acid (GABA) reuptake by inhibition of the GAT-1 transportation system, and that has no other significant pharmacodynamic effect. The relationship between intake and blood levels is linear. Usual daily maintenance doses range from 20 to 50 mg. It is completely absorbed by the gastrointestinal tract, and its half-life is approximately 7-9 h. TGB is sensitive to enzyme induction: when coprescribed with enzyme-inducing AEDs, its half-life is shortened to 2-3 h, whereas the daily dosage has to be increased into the upper range. It should be given 3 times per day. Placebo-controlled, double-blind, add-on studies conducted in patients with drug-resistant focal epilepsies have demonstrated its efficacy and overall safety. The clinical benefits appear to persist over time. Data on its use in monotherapy are scanty. The efficacy and tolerability of TGB in the pediatric age still remain to be investigated adequately. In daily practice, TGB appears to be a safe drug, but mild to moderate side effects are frequently seen, especially during titration: these include dizziness and fatigue, and are clearly abated when the drug is absorbed during meals. Titration should be especially slow, no faster than 5 mg weekly. Clinicians also should beware of the possible occurrence of confusion, which may be misdiagnosed as absence status, a short-lasting, quickly reversible central nervous system-related side effect that appears to be correlated with the peak plasma concentrations of TGB. Particularly beneficial indications for TGB and/or AED associations including TGB have not been pointed out, but there is a hint that it works best in temporal lobe epilepsies.

Tiagabine: efficacy and safety in adjunctive treatment of partial seizures

PURPOSE

To assess the efficacy and safety of tiagabine (TGB), a new antiepileptic drug (AED), as add-on therapy in patients with refractory partial seizures.

METHODS

This response-dependent study used an open-label screening phase (in which patients were titrated to their optimal TGB dose, < or =64 mg/day) followed by a double-blind, placebo-controlled, crossover phase. Initial eligibility criteria included (a) seizures inadequately controlled by existing AEDs, and (b) six or more partial seizures during an 8-week baseline period. Patients showing benefit from TGB (> or =25% reduction in total seizure rate relative to baseline) were eligible for randomization into the double-blind phase, which comprised two 7-week assessment periods separated by a 3-week crossover period.

RESULTS

Forty-four (50%) of the 88 enrolled patients entered the double-blind phase of the study during which there were significant reductions compared with placebo in all partial (p < 0.01), complex partial (p < 0.001), and secondarily generalized tonic-clonic seizure rates (p < 0.05). Thirty-three percent of patients experienced a reduction of > or =50% in the all partial seizure rate. Eight (22%) patients receiving TGB during the double-blind phase reported adverse events, of which dizziness and incoordination were the most frequent. Three patients withdrew from treatment during the double-blind phase because of adverse events; two during treatment with TGB and one during treatment with placebo. TGB did not affect plasma concentrations of other coadministered AEDs.

CONCLUSIONS

TGB was significantly better than placebo in terms of seizure rate reduction and was generally well-tolerated in patients with difficult to control seizures.

Treatment of epilepsy in the multiply handicapped

The medical management of epilepsy in the multi-handicapped patient requires careful evaluation, classification, and pharmacologic treatment. It is estimated that 20-40% of patients with mental retardation and cerebral palsy have epilepsy. This review reports the clinical trial data and personal experience related to the use of newer AEDs in the chronic management of epilepsy syndromes in children and adults, as well as information available on the treatment of seizures in individuals with mental retardation and associated handicaps. Furthermore, clusters of seizures, prolonged seizures and status epilepticus are more commonly seen in the multiply handicapped and mentally retarded population and require special attention. The new antiepileptic drugs felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine, topiramate, vigabatrin and zonisamide show specific advantage in some multiply handicapped patients, be it for seizure control or medication tolerance. Furthermore, new modalities of treatment for prolonged seizures allow better efficacy both outside of hospital and within hospital facilities. The treatment of epilepsy in multi-handicapped and retarded adults and children has significantly advanced in the past few years, and much of this improvement can be attributed to improved knowledge and monitoring of new antiepileptic drugs. Conventional anticonvulsants remain first line therapy for most clinicians, but newer AEDs must broaden the therapeutic option and do allow improved therapy for some multiply handicapped patients.

Pharmacology and clinical experience with tiagabine

Tiagabine (TGB), a recently approved anti-epileptic drug (AED), has a specific and unique mechanism of action involving the inhibition of gamma-aminobutyric acid (GABA) re-uptake into neurones and glia. TGB is potent and has linear and predictable pharmacokinetics. It does not induce or inhibit hepatic metabolism and has no clinically significant effects on the serum concentrations of other AEDs or commonly used non-AEDs. Double-blind, placebo-controlled studies in primarily hepatic enzyme-induced patients showed that TGB 30 - 56 mg/day is an effective add-on treatment for all subtypes of partial seizures. The most common adverse effects in the trials were dizziness, asthenia (weakness), somnolence, accidental injury, infection, headache, nausea and nervousness. These side effects were usually mild to moderate in severity and generally did not require medical intervention. Long-term safety studies show continued efficacy of TGB over time and no evidence of tolerance for efficacy. Open studies confirm that patients with medically refractory partial epilepsy can be successfully converted to TGB monotherapy and that TGB may be effective for other seizure types, such as infantile spasms.

Tiagabine adjunctive therapy in children with refractory epilepsy: a single-blind dose escalating study

Tiagabine, a specific gamma-aminobutyric acid-uptake inhibitor, has been shown to be reasonably well tolerated and efficacious as adjunctive treatment for partial seizures in adults and is now being investigated in children. This 4-month, single-blind study evaluated the tolerability, safety and preliminary efficacy of ascending doses (0.25-1.5 mg/kg/day) of tiagabine add-on therapy in 52 children over the age of 2 years with different syndromes of refractory epilepsy. Adverse events, mostly mild to moderate, were reported by 39% of children during the single-blind placebo period and by 83% of children during tiagabine treatment. The events predominantly affected the nervous system with asthenia (19%), nervousness (19%), dizziness (17%) and somnolence (17%) being the most common. Only three children (6%) withdrew because of adverse events. Tiagabine appeared to reduce seizures more in localisation-related epilepsy syndromes than in generalised epilepsy syndromes. Twenty-three patients with localisation-related epilepsy syndromes were included and 17 of these patients entered the fourth dosing period. The 17 patients had a median reduction of seizure rate in the fourth month of treatment of 33% compared with baseline. In comparison, 13 of 22 children with seven different generalised epilepsy syndromes entered the fourth dosing period with a median change of seizure rate of 0%. Two patients experienced single episodes of status epilepticus during treatment; both cases resolved. Tiagabine showed efficacy mainly in localisation-related syndromes and was well tolerated by most children in a group of very refractory patients and warrants further study in children with epilepsy.

Two different anticonvulsant actions of tiagabine in developing rats

PURPOSE

Our goal was to study the anticonvulsant action of tiagabine (TGB) at different levels of brain maturation in rats.

METHODS

Wistar rats in five age groups (7, 12, 18, 25, and 90 days old) were injected intraperitoneally with TGB at doses of 0.5-32 mg/kg. Thirty minutes later, motor seizures were induced by the subcutaneous adminstration of pentylenetetrazol (PTZ) in a dose of 100 mg/kg for all of the groups except the 18-day-old rat pups, which received a 90-mg/kg dose. The incidence and latency of two types of motor seizures, minimal clonic and generalized tonic-clonic seizures (GTCSs), were evaluated, and the seizure severity was scored. The time profile of TGB action at the 8-mg/kg dose was studied in the 12-and 25-day-old rats.

RESULTS

Minimal clonic seizures were reliably induced in rats 18 days old or older, and the seizures were suppressed by TGB in all of these age groups. Although TGB was very effective against this type of seizure in the 18-day-old rats, the efficacy of the drug decreased with the age of the animal. GTCSs were suppressed by TGB in the adult and 25-day-old rats, and a U-shaped dose-response curve was outlined in these two groups. The 18-and 12-day-old rat pups exhibited a selective suppression of the tonic phase of GTCSs. A mixture of these two effects was observed in the youngest group. TGB demonstrated a markedly longer action in the 12-day-old rats than in the 25-day-old rats.

CONCLUSIONS

TGB exhibits anticonvulsant action against both minimal seizures and GTCSs. Ontogenetic development of these two actions is markedly different.

Tiagabine in the treatment of epilepsy--a clinical review with a guide for the prescribing physician

Tiagabine is currently recommended mainly as add-on therapy in adults and children above 12 years with partial epilepsy not satisfactorily controlled with other antiepileptic drugs. Based on available evidence and our clinical experience, tiagabine should be used preferably in patients sharing one or more of the following additional features, (i) a history of drug-induced cutaneous adverse events; (ii) mild to moderate epilepsy allowing for a slow titration and gradual onset of anticonvulsant action over a few weeks; (iii) patients for whom it is particularly important to avoid a deterioration in cognitive performance; and, (iv) patients who failed to respond to previous treatment with sodium channel blocker agents as they may particularly benefit from the introduction of tiagabine, due to its GABAergic mechanism of action. Tiagabine can also be used successfully in other patients with refractory partial epilepsy. Tiagabine is not indicated for patients with generalized or unclassified epilepsies and for patients with severely impaired liver function.

Safety of long-term treatment with tiagabine

The aim of this study was to evaluate the safety of long-term treatment with tiagabine. We reviewed the case report forms of patients with refractory partial epilepsy who took tiagabine for longer than 6 months in two long-term studies. We classified all adverse events based on severity and persistence, and recorded the dose at onset of each adverse event. We then divided patients into those treated for 6-12 months, 12-24 months and > 24 months. We compared the adverse event profile and change in seizure frequency among the three groups. Forty-two patients took tiagabine for longer than 6 months. The mean duration of treatment was 22.6 months. The mean monthly seizure frequency was 12.7 at baseline and 8.1 at study termination (36% decrease). The most common adverse events were: tiredness (56%), headache (46%), dizziness (44%), visual symptoms (blurring, difficulty focusing, diplopia) (39%), altered mentation (32%), and tremor (31%). The adverse event profile was comparable among the three groups. Seizure frequency was significantly more improved in the > 24 months group. Long-term treatment with tiagabine is well tolerated. The most important predictor of long-term therapy with tiagabine was the degree of seizure improvement.

Treatment of epilepsy in the new millennium

Treatment options for epilepsy have increased markedly since 1990, when only carbamazepine, phenytoin, phenobarbital, primidone, and valproate were used commonly for partial and secondarily generalized seizures. Those with primary generalized seizures received ethosuximide or valproate. Over the past decade, however, additional agents have been introduced, with the promise of improved seizure control and minimal side effects. The new antiepileptic drugs (AEDs)-felbamate, gabapentin, lamotrigine, tiagabine, topiramate, vigabatrin and oxcarbazepine-have demonstrated superior efficacy for some with refractory epilepsy. In addition, the new agents frequently are better tolerated when used as monotherapy or adjunctive therapy. The optimal place for the new AED will require additional studies and careful postmarketing surveillance and assessments. Although these AEDs offer benefits, not all patients with epilepsy have responded. Thus, the search for new AEDs continues.

Enzyme induction and inhibition by new antiepileptic drugs: a review of human studies

The aim of this paper is to review a number of new antiepileptic agents (i.e. felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine, topiramate, vigabatrin and zonisamide) for their inducing and/or inhibitory properties in humans, mainly considering the interactions where they are involved as the cause rather than the object of such interactions. Two aspects have been particularly taken into account: the changes or absence of changes in plasma/serum concentrations of concomitant drugs and the direct or indirect evidence of induction, inhibition or lack of effect on the six major human hepatic CYP isozymes (CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1 and CYP3A4), as well as on other CYP isozymes or enzyme systems. Felbamate clearly affects the pharmacokinetics of a number of drugs, generally increasing but also decreasing their concentrations. It induces enzymes such as CYP3A4 and inhibits enzymes such as CYP2C19 and those of the beta-oxidation pathway. Topiramate is not devoid of potential interaction properties: it decreases the plasma concentrations of ethinylestradiol, induces CYP3A4 and inhibits CYP2C19. For oxcarbazepine, no inhibitory, only inductive effects have been observed thus far. Felbamate. topiramate and oxcarbazepine may induce the metabolism of steroidal oral contraceptives. In this respect, tiagabine has been studied at a rather low dose. Pharmacodynamic or pharmacokinetic interaction seems to exist between lamotrigine and carbamazepine. Lamotrigine appears to be a weak inducer of UGTs, whereas induction of CYP3A4 seems improbable as the compound does not change the concentrations of oral contraceptives or the urinary excretion of 6beta-hydroxycortisol. Zonisamide has very peculiar pharmacokinetics and an extensive metabolism. Additional information on its enzyme inducing or inhibiting properties would be necessary, as data so far collected on its effect on the pharmacokinetics of other drugs are conflicting. Gabapentin, vigabatrin and in particular levetiracetam appear to be devoid of significant enzyme inducing or inhibiting properties.

Newer anticonvulsants: comparative review of drug interactions and adverse effects

The tolerability and drug interaction profiles of 6 new anticonvulsants: oxcarbazepine, vigabatrin, lamotrigine, gabapentin, tiagabine and topiramate, are reviewed. In general, these new anticonvulsants are well tolerated and drug interaction problems are minor with the exception of the risk of failure of oral contraceptives during treatment with oxcarbazepine or topiramate. In this review, the clinical implications of the tolerability of these drugs are discussed for different patient groups. The choice of which new anticonvulsant for which patient depends upon individual factors, in particular, seizure type, tolerability and practical administration factors. Treating elderly patients may be complicated by an increased sensitivity to adverse effects as these patients very often receive polytherapy for accompanying diseases. Drugs with very simple pharmacokinetic properties may be preferred in this group. Women of childbearing age face specific problems related to the epilepsy and to treatment with anticonvulsants. These include impaired fertility, failure of oral contraceptives and the risk of birth defects. Some new anticonvulsants may be suggested in preference to classical drugs to avoid these problems, but the human experience with newer anticonvulsants is still limited and, therefore, so is knowledge of the risk of congenital malformations in the offspring of mothers taking anticonvulsants. Psychiatric and behavioural changes frequently complicate treatment of patients with mental retardation. Some of the new anticonvulsants, in particular those affecting the gamma-aminobutyric acid (GABA) system such as vigabatrin, seem to exacerbate this problem and should be used with caution in these patients.

New anti-epileptic drugs for the 21st century

Prior to 1993, there were only six major drugs available in the US for the treatment of patients with epilepsy. These included phenobarbital (PB), phenytoin (PHT), carbamazepine (CBZ), primidone (PRIM), valproic acid/sodium valproate (VPA) and ethosuximide (ESX). Of these drugs, VPA has the broadest spectrum of activity and ESX the most limited. Despite these six agents, as well as several secondary drugs, it is estimated that over 30% of patients have inadequate seizure control, while others, whose disease is adequately controlled, suffer from bothersome adverse events (AEs). Since 1993, ten new drugs have entered the worldwide market (not all in the US). Those released include felbamate (FBM), gabapentin (GBP), lamotrigine (LTG), topiramate (TPM), tiagabine (TGB), oxcarbazepine (OXC), levetiracetam (LVT), zonisamide (ZNS), clobazam (CLB) and vigabatrin (VGB). The purpose of this article is to review each of the above drugs, looking at efficacy, safety, tolerability and where they may play a role in the current treatment of epilepsy.

New antiepileptic drugs in children: which ones for which seizures?

Until 1993, carbamazepine (CBZ), phenytoin (PHT), phenobarbital (PB), and valproate (VPA) accounted for the great majority of the prescriptions written for the treatment of epilepsy. Since 1993, five antiepileptic drugs (AEDs) have been released in the United States, and at least three additional drugs are expected to be released by the end of the year 2000. As a group, these newer drugs differ from the established drugs in terms of their pharmacokinetics, interaction potential, and adverse effects. In addition, any one of the newer drugs may achieve seizure control in situations in which an established drug had not. The newer drugs certainly represent a welcome addition to the existing options for the treatment of epilepsy in children. However, the availability of several new AEDs represents a therapeutic dilemma for the clinician because optimal use of these drugs has not yet been established. This is particularly true in children because (i) newer drugs are often studied less frequently in children, (ii) pharmacokinetics in children differ from those in adults, (iii) children may have different adverse effects, and (iv) children have a broader spectrum of various seizure types and epilepsy syndromes. In the first part of this review, the clinical pharmacology of the currently available newer AEDs is discussed individually, with special emphasis on data in children. In particular, pharmacokinetics, interactions, dosage and titration, efficacy spectrum, and adverse effect profile is discussed for each drug. In the second part, an attempt is made to determine the place for the newer drugs in the treatment of the different pediatric seizures and epilepsy syndromes.

Tiagabine: absence of kinetic or dynamic interactions with ethanol

Tiagabine is a new antiepileptic drug that inhibits the uptake of gamma-aminobutyric acid into neurons and glia. This double-blind, placebo-controlled study investigated the effect of multiple doses of tiagabine on the adverse cognitive effects produced by a single dose of ethanol in 20 healthy volunteers. The effects of each drug on the pharmaco-kinetics of the other were also determined. Compared with placebo, tiagabine produced no statistically significant effects on digit vigilance speed (primary assessment variable) or accuracy, choice reaction time, immediate or delayed word recall, delayed word recognition speed or sensitivity, visual tracking, body sway, or subjective measures of alertness, calmness, and contentment. There was no evidence of a pharmacodynamic interaction between tiagabine and ethanol with respect to these variables. The pharmacokinetic parameters of tiagabine and ethanol (maximum plasma concentration [Cmax], time to Cmax and area under the plasma concentration-time curve) were unchanged during concomitant administration. Adverse events, which mainly affected the central nervous system, occurred with a similar incidence during tiagabine and placebo administration and were more common after the administration of ethanol. There appears to be no need for additional caution regarding driving or operating machinery when ethanol is administered to patients taking tiagabine.

Basic mechanisms of gabitril (tiagabine) and future potential developments

Gabitril (tiagabine) is a potent selective inhibitor of the principal neuronal gamma-aminobutyric acid (GABA) transporter (GAT-1) in the cortex and hippocampus. By slowing the reuptake of synaptically-released GABA, it prolongs inhibitory postsynaptic potentials. In animal models of epilepsy, tiagabine is particularly effective against kindled (limbic) seizures and against reflexly-induced generalized convulsive seizures. These data are predictive of its efficacy in complex partial seizures in humans. Possible clinical applications outside the field of epilepsy include bipolar disorder and pain.

Review of controlled trials of gabitril (tiagabine): a clinician's viewpoint

A recent problem for doctors has been the choice of which new antiepileptic drug (AED) to select for treatment of pharmacoresistant epilepsy. This article summarizes the clinical experience to date regarding the efficacy and safety of tiagabine (TGB; Gabitril) as adjunctive therapy in patients with partial-onset seizures. In its early Phase II development, TGB was evaluated in two multicenter pilot studies. Each had an open-label enrichment phase followed by a treatment phase with randomized, double-blind, two-period, cross-over phases. Between 24 and 50% of patients experienced reductions in seizure rates of > or =50%, depending on the type of partial seizure. In Phase III, three double-blind, parallel group, placebo-controlled adjunctive studies determined the efficacy of TGB in patients with refractory partial seizures. The first was a dose-response study employing doses of TGB-HCl of 16, 32 or 56 mg/day. Significant reductions in seizure rates were found with 32 and 56 mg/day. The second and third studies evaluated the efficacy of dosing TGB twice, three times, and four times daily, all of which showed similar efficacy. TGB efficacy in partial seizures was supported in several open trials, and no tolerance to efficacy was noted in long-term continuation studies. Tolerability was documented in all trials. Most adverse events were mild or moderate and transient, occurring during dose titration. They were clearly dose-related. No relevant changes in hematologic and biochemical tests, vital signs, or body weight were attributable to TGB. TGB appears to be an effective new drug for partial seizures with an acceptable safety profile.

Age-dependence of the anticonvulsant effects of the GABA uptake inhibitor tiagabine in vitro

Epileptic syndromes frequently start at childhood and therefore it is crucial to test new anticonvulsants at immature stages of the nervous system. We compared the effects of the gamma-aminobutyric acid (GABA) uptake inhibitor tiagabine [(R)-N-(4, 4-bis(3-methyl-2-thienyl)but)3-en-1-yl nipecotic acid] on low-Mg(2+)-induced epileptic discharges in brain slices from rat pups (p 5-8) and juvenile animals (p 15-20). In tissue from rat pups, tiagabine slightly reduced epileptiform activity in hippocampal area CA1 but had no effect in the entorhinal cortex. In juvenile rats, epileptiform discharges were unaffected in CA1 but suppressed by 60% in the entorhinal cortex. While tiagabine increases its efficacy with age, in-situ hybridisation and PCR analysis show that mRNA coding for the neuronal GABA-transporter GAT-1 is already present at p 5. We therefore conclude that the increasing efficacy of tiagabine during ontogenesis is due to functional maturation of GABAergic synapses rather than to up-regulation of GAT-1 expression.

Managing pediatric epilepsy syndromes with new antiepileptic drugs

The management of epilepsy in the pediatric patient requires careful evaluation, classification, and pharmacologic treatment. Despite best efforts on the part of clinicians, approximately 25% of children remain refractory to appropriate medical therapies. The development of an improved classification system and the emergence of several new antiepileptic drugs have enabled some progress in this area, specifically in children with disorders such as Lennox-Gastaut syndrome and infantile spasms, which are notoriously difficult to control. However, limited data are available that define the optimal use of new antiepileptic agents in pediatric patients. To most effectively treat children with epilepsy syndromes, further research must be completed to validate the positive effects described in case reports, open-label clinical trials, and early controlled clinical trials.

Use of new antiepileptic drugs in the treatment of childhood epilepsy

The management of epilepsy in children requires careful evaluation, classification, and pharmacologic treatment. With classic antiepileptic drugs (AEDs), at least 25% of children remain refractory to appropriate therapy. The past decade has allowed the introduction of a number of newer AEDs for treatment of both adults and children with epilepsy. These include felbamate, gabapentin, lamotrigine, topiramate, tiagabine, and vigabatrin. Emerging information regarding the efficacy of these AEDs in treating childhood epilepsy syndromes suggests advantages for many patients. Limited data are available that define the optimal use of new AEDs in pediatric patients. Further research must be completed to validate the positive effects described in existing clinical trials of the new AEDs in the treatment of childhood epilepsy.

Tiagabine

Tiagabine (TGB) is a recently approved antiepileptic drug (AED) that inhibits y-aminobutyric acid (GABA) reuptake into neurons and glia, a mechanism of action that is specific and unique among the AEDs. TGB is potent and has linear and predictable pharmacokinetics. It has no clinically relevant effects on hepatic metabolism or serum concentrations of other AEDs, effects on laboratory values, or interactions with common non-AEDs. TGB is effective as add-on therapy for partial seizures in patients with medically refractory epilepsy in doses ranging from 30 to 56 mg daily. Conversion to TGB monotherapy can be achieved in patients with medically refractory epilepsy, although additional controlled studies are needed to confirm the efficacy of TGB as monotherapy and to establish the effective dosage range. In controlled studies, the most common adverse events of TGB are dizziness, asthenia, somnolence, accidental injury, infection, headache, nausea, and nervousness. These are usually mild to moderate in severity and almost always resolve without medical intervention.

Absence of interaction between tiagabine, a new antiepileptic drug, and the benzodiazepine triazolam

In a randomised, double blind, placebo-controlled, four-period cross-over study in 12 healthy volunteers, the potential pharmacodynamic and pharmacokinetic interactions between the new antiepileptic drug, tiagabine, and the benzodiazepine, triazolam, were investigated. A single dose of tiagabine HCl 10 mg did not enhance the sedative or cognitive effects of a single dose of the benzodiazepine triazolam 0.125 mg, although the time-course of the effects was prolonged. Furthermore, tiagabine did not produce any statistically significant effects on the pharmacokinetics of triazolam. Similarly, the pharmacokinetics of tiagabine were not modified by triazolam. Tiagabine was well tolerated when administered alone or with triazolam.

New antiepileptic drugs: comparison of key clinical trials

PURPOSE

Data accrued from clinical trials of five new antiepileptic drugs (AEDs) are compared for efficacy in reducing seizures and self-reported adverse events as a basis of selection among new AEDs. Drawbacks to use of these data also are demonstrated.

METHODS

A review of double-blind, placebo-controlled clinical trials of a new AED or placebo added to a standard AED provided data on reduction of complex partial seizures (CPSs). Success is > or =50% fewer CPSs with a new AED or placebo; Overall Improvement is the success rate with drug minus the success rate with placebo. Adverse events were tabulated from product-labeling lists of COSTART items (incidence, > or =5%). The Summary Complaint score is the total number of reports of individual events for each AED.

RESULTS

Efficacy data demonstrate differences in Overall Improvement rates among five new AEDs and placebos (p = 0.001). However, rates of response to placebo also differed significantly among trials (p = 0.01). Adverse events predominantly affect central nervous system, psychiatric, and general body systems. However, patients in the placebo control groups did not consistently report adverse effects. Summary Complaint scores differ among the five new AEDs, but variability in use of COSTART terms nullifies comparisons.

CONCLUSIONS

Comparisons of data for five new AEDs provide information for selection among treatments when a second drug is needed to improve control of CPSs. However, significant differences among the control groups and other problems make comparisons between trials problematic. The final choice should be based on the need of the individual patient for superior seizure control versus minimal adverse effects.

Tiagabine: a novel antiepileptic drug

OBJECTIVE

To provide a comprehensive review of tiagabine, including its pharmacology, toxicology, pharmacokinetics, drug interactions, efficacy, adverse effects, and dosing recommendations.

DATA SOURCES

A computerized search of the MEDLINE database from 1966 to December 1997 was used to identify publications related to tiagabine and nipecotic acid derivatives. Included in this review was information gathered from scientific meetings. Manufacturer's information was used when there was no primary literature.

DATA SYNTHESIS

Tiagabine amplifies gamma-aminobutyric acid (GABA) neurotransmission, the predominant inhibitory neurotransmitter in the brain. Its mechanism of action is selective and has shown promise as an antiepileptic drug (AED) in patients with seizures refractory to other pharmaceutical products. Tiagabine exhibits dose-independent absorption, 90-95% bioavailability, high protein binding (96%), metabolism via hepatic cytochrome P450 enzymes (CYP3A subfamily), and displays first-order elimination pharmacokinetics. The mean plasma half-life is 5-8 hours. Concomitant medications that induce hepatic metabolism enhance tiagabine elimination; metabolism is reduced in patients with hepatic dysfunction. Adverse events of tiagabine typically involve the central nervous system, have been mild to moderate in intensity, and also have been transient in nature.

CONCLUSIONS

Tiagabine has demonstrated a good safety profile and, while it has not been demonstrated to be superior to other second-line AEDs for partial seizures, its safety and select mechanism of action warrant its further evaluation in the clinical setting. Tiagabine should be a good alternative add-on agent for patients with unsatisfactory seizure control or intolerable adverse effects of traditional therapies; thus, this agent should be made available to these patients.

Novel synthesis and release of GABA in cerebellar granule cell cultures after infection with defective herpes simplex virus vectors expressing glutamic acid decarboxylase

The inhibitory amino acid neurotransmitter gamma-aminobutyric acid (GABA) is synthesized from glutamate in a single step by the enzyme glutamatic acid decarboxylase (GAD). We sought to determine whether viral vectors containing GAD cDNA could be used to enhance synthesis and stimulation-evoked release of GABA in cultures of CNS neurons. For this purpose, we generated double-cassette defective herpes simplex virus (HSV) vectors that expressed one of the two GAD isoforms (GAD65 or GAD67), and Escherichia coli LacZ. Infection of cerebellar granule cell (CGC) cultures with vectors containing GAD cDNA resulted in a significant increase in isoform-specific expression of GAD, synthesis of GABA, and stimulation-evoked GABA release. GAD65 and GAD67 vector-infected neurons exhibited a comparable profile of GABA levels, synthesis and release, as well as GAD protein distribution. In CGCs cultured for 6 days in vitro (DIV), GABA synthesized after vector-derived GAD expression was released by treatment with glutamate or veratridine, but only in a Ca2+-independent fashion. In more mature (10 DIV) cultures, both Ca2+-dependent, K+ depolarization-induced, as well as Ca2+-independent, veratridine-induced, GABA release was significantly enhanced by GAD vector infection. Treatment of CGCs with kainic acid, which destroys most of the GABAergic neurons (<1% remaining), did not prevent vector-derived expression of GAD nor synthesis of GABA. This suggests that defective HSV vector-derived GAD expression can be used to increase GABA synthesis and release in CNS tissue, even in the relative absence of GABAergic neurons. The use of such GAD vectors in the CNS has potential therapeutic value in neurologic disorders such as epilepsy, chronic pain, Parkinson's and Huntington's disease.