Tiagabine versus phenytoin and carbamazepine as add-on therapies: effects on abilities, adjustment, and mood

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 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.

The cognitive impact of antiepileptic drugs

Effective treatment of epilepsy depends on medication compliance across a lifetime, and studies indicate that drug tolerability is a significant limiting factor in medication maintenance. Available antiepileptic drugs (AEDs) have the potential to exert detrimental effects on cognitive function and therefore compromise patient wellbeing. On the other hand, some agents may serve to enhance cognitive function. In this review paper, we highlight the range of effects on cognition linked to a variety of newer and older AEDs, encompassing key alterations in both specific executive abilities and broader neuropsychological functions. Importantly, the data reviewed suggest that the effects exerted by an AED could vary depending on both patient characteristics and drug-related variables. However, there are considerable difficulties in evaluating the available evidence. Many studies have failed to investigate the influence of patient and treatment variables on cognitive functioning. Other difficulties include variation across studies in relation to design, treatment group and assessment tools, poor reporting of methodology and poor specification of the cognitive abilities assessed. Focused and rigorous experimental designs including a range of cognitive measures assessing more precisely defined abilities are needed to fill the gaps in our knowledge and follow up reported patterns in the literature. Longitudinal studies are needed to improve our understanding of the influence of factors such as age, tolerance and the stability of cognitive effects. Future trials comparing the effects of commonly prescribed agents across patient subgroups will offer critical insight into the role of patient characteristics in determining the cognitive impact of particular AEDs.

Psychiatric symptomatologies and disorders related to epilepsy and antiepileptic medications

INTRODUCTION

Psychiatric comorbidities (such as depression, anxiety, psychosis, inattention, obsession, personality traits, aggression and suicide) are frequent in patients with epilepsy and have a significant impact on medical management and quality of life.

AREAS COVERED

A literature search was performed in MEDLINE for epidemiological, longitudinal, prospective, double-blind clinical trial studies published between 1990 and 2011 using the following words: epilepsy, antiepileptic drugs (AEDs), behavioral/emotional/psychiatric comorbidities, suicide and aggression. In this review, the author discusses: i) the characterization and prevalence of behavioral disturbances associated with epilepsy, ii) variables correlated with behavioral comorbidities which include: psychosocial-, clinical- and treatment-related variables, iii) the complex mechanisms of behavioral comorbidities associated with epilepsy, which include both psychosocial (functional) and organic; the process of epileptogenesis, neuronal plasticity, abnormalities in hypothalamic-pituitary axis and neurotransmitters and pathways are fundamental determinants, iv) the negative psychotropic effects of AEDs and their mechanisms and v) the suggested biopsychosocial model of management (pharmacological and non-pharmacological).

EXPERT OPINION

The relationship between psychiatric disorders and epilepsy has relevant therapeutic implications which should be directed towards a comprehensive biopsychosocial approach that focuses on the whole person rather than simply on the disease process.

Antiepileptic drug-induced cognitive adverse effects: potential mechanisms and contributing factors

Cognitive dysfunction is frequently observed in patients with epilepsy and represents an important challenge in the management of patients with this disorder. In this respect, the relative contribution of antiepileptic drugs (AEDs) is of relevance. The fact that a considerable number of patients require AED therapy for many years, or perhaps even a lifetime, emphasizes the need to focus on the long-term adverse effects of these drugs on cognition. The most prevalent of the CNS adverse effects observed during AED therapy are sedation, somnolence, distractibility, insomnia and dizziness. Sedation, in particular, is associated with most of the commonly used AED therapies. Nevertheless, cognitive function in individuals with epilepsy may also be influenced by several factors, of which AEDs constitute only one of many putative causes. In general terms, most studies agree that some differences exist among the older AEDs with regard to the effects on cognition, and some newer generation molecules may have a better cognitive profile than older AEDs. The mechanisms of action are an obvious determinant; however, there is still a lack of evidence for differentiation between available drugs with regard to cognitive effects. Some authors have suggested that there may be different cognitive effects associated with individual drugs; however, the question as to whether there are more specific deficits related to the action of individual drugs remains unsolved. There seems to be agreement that polytherapy and high-dose treatment can produce cognitive adverse effects and when high dosages or adjunctive polytherapy is needed, the balance between benefits and disadvantages may be negatively biased against drug treatment. Thus, drug treatment requires careful balancing in the attempt to reach maximal seizure control while avoiding neurotoxic adverse effects. Finally, the mood status of the patient and clinical relevance of the information obtained by neuropsychological testing represent important variables that need to be taken into account when discussing cognitive adverse effects of AEDs.

The aspects and mechanisms of cognitive alterations in epilepsy: the role of antiepileptic medications

Epilepsy is a major health problem. Several studies suggest a significant influence of epilepsy and its treatment on dynamic and functional properties of brain activity. Epilepsy can adversely affect mental development, cognition, and behavior. Epileptic patients may experience reduced intelligence, attention, and problems in memory, language, and frontal executive functions. Neuropsychological, functional, and quantitative neuroimaging studies revealed that epilepsy affect the brain as a whole. Mechanisms of epilepsy-related cognitive dysfunction are poorly delineated. Cognitive deficits with epilepsy may be transient, persistent, or progressive. Transient disruption of cognitive encoding processes may occur with paroxysmal focal or generalized epileptic discharges, whereas epileptogenesis-related neuronal plasticity, reorganization, sprouting, and impairment of cellular metabolism are fundamental determinants for progressive cognitive deterioration. Also antiepileptic drugs (AEDs) have differential, reversible, and sometimes cumulative cognitive adverse consequences. AEDs not only reduce neuronal irritability but also may impair neuronal excitability, neurotransmitter release, enzymes, and factors critical for information processing and memory. The present article serves as an overview of recent studies in adult and childhood epilepsy literatures present in PubMed that highlighted cognitive evaluation in epilepsy field (publications till 2008 were checked). We also checked the reference lists of the retrieved studies for additional reports of relevant studies, in addition to our experience in this field. Our search revealed that although the aspects of cognitive dysfunction, risk factors, and consequences have been explored in many studies; however, the mechanisms of contribution of epilepsy-related variables, including AEDs, to patients' cognition are largely unexplored. In this review, we discussed the differential effect of AEDs in mature and immature brains and the known mechanisms underlying epilepsy and AEDs adverse effects on cognition. The nature, timing, course, and mechanisms of cognitive alteration with epilepsy and its medications are of considerable clinical and research implications.

Do recent seizures and recent changes in antiepileptic drugs impact performances on neuropsychological tests in subtle ways that might easily be missed?

PURPOSE

The possibility that a recent seizure or a recent change in antiepileptic medication might produce an occult change in neuropsychological performance is of interest, and especially so in the context of evaluation for epilepsy surgery. Such an evaluation is often done in a setting of video-EEG monitoring where a strong effort is made to produce seizures as quickly as possible with abrupt changes in medication, alterations in sleep, etc., which could impact the validity of neuropsychological findings.

METHODS

A total of 126 adults were studied who had seizures of strictly temporal origin (47 right, 79 left) and whose recent medication history and seizure occurrence prior to testing was as clear as possible. All were tested with an extensive neuropsychological battery with great attention to giving tests only when the patients appeared clinically not to be suffering from recent seizures (seizures occurring on the day of testing or on the day prior to testing) or medication change effects. The cognitive correlates of side of seizures were also evaluated in order to provide a strength-of-effect comparison with recency of AED changes and seizures.

RESULTS

Findings from three-way ANOVA showed a possible slight adverse effect of recent AED change, no effects of recent seizures, and a sizeable relationship with side of seizures. A simultaneous consideration of all three of these variables did not provide additional findings of interest.

CONCLUSIONS

Although it is not possible to completely rule out some subtle cognitive effects of recent changes in medication or recent seizures, this investigation does not provide evidence for such effects when the neuropsychological evaluation is conducted carefully with no testing during any questionable or definite postictal periods.

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.

Efficacy and cognitive side effects of tiagabine and topiramate in patients with epilepsy

OBJECTIVE

Whereas the efficacy of the newer antiepileptic drugs (AEDs) is well established, there remain questions regarding their cognitive side effects. Therefore, we performed a comparative open randomized trial with TPM and TGB as add-on therapy, with particular consideration of cognition, mood, and health-related quality of life (HRQOL).

METHODS

Forty-one patients with refractory epilepsy were randomly assigned to one of the two treatment groups (TPM vs TGB) and received neuropsychological testing at baseline (T1), after titration (3 months, T2), and during the maintenance phase (another 3 months, T3). Tests included measures of intelligence, attention, working memory, episodic memory, language, and self-report questionnaires regarding mood and HRQOL. Twenty patients (8 TPM, 12 TGB) discontinued the trial for different reasons (no group difference).

RESULTS

Seizure outcome (intention-to-treat analysis) was comparably good in both groups (8.1% seizure free, 29.7% seizure reduction>50%). From baseline to after the titration paired sample t tests revealed significant deterioration in verbal fluency, language comprehension, working memory, and visual block tapping under TPM and a deterioration in verbal memory (delayed free recall) in the TGB group. These functions remained stable in the maintenance phase. Self-report measures initially indicated concerns about AED side effects in both groups and concerns about worse cognitive functioning and depression under TPM. In the maintenance phase the TGB group reported feeling a lack of energy, whereas patients on TPM demonstrated improvement on all QOLIE scales on a descriptive level.

CONCLUSION

This study demonstrates the comparable efficacy of TPM and TGB. Consistent with previous reports, TPM but not TGB appears to be associated with persistent negative cognitive side effects on frontal lobe-associated functions, the degree of which may be estimated by the fact that this effect was observed with a very small sample size. In contrast, in patients taking TPM, initially negatively affected HRQOL returns to baseline in the long run on a descriptive level. The latter finding may be interpreted in accordance with the observation that objective performance and subjective self-report under TPM can be dissociated.

GABA transporter deficiency causes tremor, ataxia, nervousness, and increased GABA-induced tonic conductance in cerebellum

GABA transporter subtype 1 (GAT1) knock-out (KO) mice display normal reproduction and life span but have reduced body weight (female, -10%; male, -20%) and higher body temperature fluctuations in the 0.2-1.5/h frequency range. Mouse GAT1 (mGAT1) KO mice exhibit motor disorders, including gait abnormality, constant 25-32 Hz tremor, which is aggravated by flunitrazepam, reduced rotarod performance, and reduced locomotor activity in the home cage. Open-field tests show delayed exploratory activity, reduced rearing, and reduced visits to the central area, with no change in the total distance traveled. The mGAT1 KO mice display no difference in acoustic startle response but exhibit a deficiency in prepulse inhibition. These open-field and prepulse inhibition results suggest that the mGAT1 KO mice display mild anxiety or nervousness. The compromised GABA uptake in mGAT1 KO mice results in an increased GABA(A) receptor-mediated tonic conductance in both cerebellar granule and Purkinje cells. The reduced rate of GABA clearance from the synaptic cleft is probably responsible for the slower decay of spontaneous IPSCs in cerebellar granule cells. There is little or no compensatory change in other proteins or structures related to GABA transmission in the mGAT1 KO mice, including GAT1-independent GABA uptake, number of GABAergic interneurons, and GABA(A)-, vesicular GABA transporter-, GAD65-, and GAT3-immunoreactive structures in cerebellum or hippocampus. Therefore, the excessive extracellular GABA present in mGAT1 KO mice results in behaviors that partially phenocopy the clinical side effects of tiagabine, suggesting that these side effects are inherent to a therapeutic strategy that targets the widely expressed GAT1 transporter system.

Determining the effects of antiepileptic drugs on cognitive function in pediatric patients with epilepsy

The majority of children with epilepsy are of normal intelligence; however, a significant subset suffers from temporary or permanent cognitive impairment. Factors that affect cognitive function are myriad and include the neuropathology underlying the epilepsy, seizures, epileptiform activity, psychosocial problems, and antiepileptic drug side effects. Although cognitive impairment is often wrongly attributed to the effects of antiepileptic drugs, antiepileptic drugs do impair cognition in some children. Clinicians should be aware of the differential cognitive effects of antiepileptic drugs and should monitor cognitive function closely when adding or changing therapy. Based on published data from prospective, chronic dosing studies, phenobarbital and topiramate have the highest potential for causing cognitive dysfunction.

Multidisciplinary approach to childhood epilepsy: exploring the scientific rationale and practical aspects of implementation

The management of childhood epilepsy requires attention to more than seizure control because children with epilepsy often suffer from comorbidities that lead to an increased frequency of psychiatric disease, learning difficulties, and other problems of psychosocial development. These comorbidities can stem in part from the same genetic traits that determine seizure susceptibility. Thus, mutations affecting potassium, calcium, and sodium channels have been linked with epilepsy syndromes and affective and behavioral abnormalities. It is important to consider the effect of antiepilepsy drugs on comorbid conditions and the effect on seizures of drugs used to treat comorbidities. A number of antiepilepsy drugs are available that have minimal adverse cognitive effects, and some can have positive effects on mood and behavior. Epilepsy in a child is a condition that affects and is affected by the entire family situation. In addition to appropriate neuropsychologic evaluation, optimal management of childhood epilepsy also can require the involvement of the social worker, advanced practice nurse, and educational specialist. Many elements of the multidisciplinary team approach can be instituted by the child neurologist in community practice and at large, specialized epilepsy centers.

Mood effects of antiepileptic drugs

This article reviews our knowledge about a specific subgroup of chronic CNS-related side effects of antiepileptic drugs (AED) treatment, i.e., the effects of AEDs on mood. In line with a recent hypothesis, using the experience of AED treatment in psychiatry, we examined whether mood effects are related to the known anticonvulsant mechanisms of action of the AEDs. Specifically we examined whether AEDs, acting through potentiation of GABAergic neurotransmitter release, have "sedating" effects on mood, whereas AEDs that act through the reduction of excitatory glutamate neurotransmitter release have "activating" effects on mood. The results of this review yield evidence that there are relationships between the known anticonvulsant mechanisms of action of the AEDs and mood effects. Mood effects occur especially when the drugs have a sustained effect on neuronal mechanisms, in particular when the inhibitory or excitatory neurotransmitter release is altered. Drugs with "use-dependent" impact on sodium or calcium channels probably have a more transient impact and do not lead to interictal stable mood effects. Drugs with multiple mechanisms of action seem to combine a favorable efficacy profile with an increased risk of severe mood problems. The quality of the evidence, however, is not conclusive and there are many paradoxical results. One reason for this lack of "fit" may be the use in this review of a simplified classification, based only on the predominant mechanism of action to classify a drug. Only a limited number of AEDs (ethosuximide, tiagabine) are characterized by a single anticonvulsant mechanism of action. Probably more detailed coupling of mechanisms of action (e.g., inspecting the type and route of impact on GABA release) and mood effects may give less confusing results. The use of magnetic resonance imaging techniques such as spectroscopy may provide interesting results.

Effect of antiepileptic drugs on cognitive function in individuals with epilepsy: a comparative review of newer versus older agents

Several 'new' antiepileptic drugs (AEDs), i.e. oxcarbazepine, vigabatrin, lamotrigine, zonisamide, gabapentin, tiagabine, topiramate and levetiracetam have been introduced into clinical practice within the last decade. Most of these new drugs are at least as effective as the 'old' AEDs [phenytoin, phenobarbital (phenobarbitone), valproic acid (sodium valproate) and carbamazepine] and, in general, they seem to be better tolerated than the old drugs. The new AEDs might have less influence on cognitive functions but the aspect has not been systematically studied. Neuropsychological testing has been the major method of objectively examining cognitive function related to the use of AEDs but a number of methodological problems blur the results. Alteration of cognition might reflect a chronic adverse effect of AEDs but the negative effects of the drugs are only one of several factors that may influence cognition. In addition, subjective complaints about cognitive deficits (e.g. memory problems or attention) may also reflect other aspects of adverse effects than those concerning specific cognitive functions (e.g. mood and anxiety). This review focuses on studies of the cognitive effects of the new AEDs, and in particular on studies that compare cognitive effects of the old and new drugs. In general, the new AEDs seem to display no or minor negative cognitive effects. In studies in which new AEDs have been compared with old AEDs, there was a tendency in favour of the new AEDs in some of the studies.

New antiepileptic drugs: comparative studies of efficacy and cognition

Over the past 10 years, the Food and Drug Administration has approved eight prophylactic antiepileptic drugs (AEDs). Although the goal of universal seizure control without side effects has not been reached, the tolerability of medications has improved. This paper reviews the AEDs introduced since 1993 and tries to objectively present comparative data obtained in double-blind studies.

Differential cognitive effects of antiepileptic drugs

As a group, children and adolescents with epilepsy have a higher prevalence of cognitive and behavioral disorders, although many fall within the normal distribution. For those affected, several causes have been identified, some of which may be interrelated. It has proven to be methodologically sound to isolate the role of specific antiepileptic drugs as a cause of cognitive impairment. The large body of literature that has accumulated on this topic is characterized by a relatively high proportion of inconclusive or contradictory observations. This may be due in part to the many methodological pitfalls in this area of research. The emerging picture is that cognitive effects caused by antiepileptic drugs are neither the rule nor the exception. Although certain drugs appear more likely to be involved, no single drug causes problems in every patient, and no drug can be assumed never to cause any cognitive impairment. The subgroup of patients that are at higher risk cannot be easily defined. Early detection of cognitive effects is based on actively eliciting reports of symptoms. This can be complemented by a screening battery in case of suspicion.