Cognitive and Behavioral Effects of Antiepileptic Drugs

Summary: All antiepileptic drugs (AEDs) have the potential for adverse effects on cognition and behavior. Most of the major AEDs, administered in therapeutic doses, cause little or no cognitive or behavioral impairment in group studies. However, individual variability is considerable, and some patients do not tolerate low serum levels, whereas others tolerate high levels without subjective or objective effects. In the past, carbamazepine (CBZ) and valproate (VPA) have been reported to have the fewest adverse cognitive and behavioral effects in children and adults. However, several recent, well-controlled studies have not found significant differences between the effects of phenytoin (PHT) and those of CBZ or VPA. Greater adverse effects have been found for phenobarbi-tal (PB). However, we must use environmentally relevant measures of cognitive and behavioral functioning to measure effects on daily functioning. Future studies must define cognitive and behavioral toxicity in subpopulations (e.g., post-traumatic epilepsy, mental retardation, depression) and with the new AEds.     

Effects of antiepileptic drugs on attention as assessed by a five-choice serial reaction time task in rats

Patients with epilepsy can have impaired cognitive abilities. Antiepileptic drugs (AEDs) may contribute to the cognitive deficits observed in patients with epilepsy, and have been shown to induce cognitive impairments in healthy individuals. However, there are few systematic data on the effects of AEDs on specific cognitive domains. We have previously evaluated a number of AEDs with respect to their effects on working memory. The purpose of the present study was to evaluate the effects of AEDs on attention as measured by five-choice serial reaction time behavior in nonepileptic rats. The GABA-related AEDs triazolam, phenobarbital, and chlordiazepoxide significantly disrupted performance by increasing errors of omission, whereas tiagabine, valproate, and gabapentin did not. The sodium channel blocker carbamazepine increased errors of omission at relatively high doses, whereas the sodium channel blockers phenytoin, topiramate, and lamotrigine were without significant effect. Levetiracetam had no effect on attention. The disruptions produced by triazolam, phenobarbital, chlordiazepoxide, and carbamazepine were similar in magnitude to the effects of the muscarinic cholinergic receptor antagonist scopolamine. The present results indicate that AEDs can disrupt attention, but there are differences among AEDs in the magnitude of the disruption in nonepileptic rats, with drugs that enhance GABA receptor function producing the most consistent disruption of attention.     

Effects of antiepileptic drugs on attention as assessed by a five-choice serial reaction time task in rats

Patients with epilepsy can have impaired cognitive abilities. Antiepileptic drugs (AEDs) may contribute to the cognitive deficits observed in patients with epilepsy, and have been shown to induce cognitive impairments in healthy individuals. However, there are few systematic data on the effects of AEDs on specific cognitive domains. We have previously evaluated a number of AEDs with respect to their effects on working memory. The purpose of the present study was to evaluate the effects of AEDs on attention as measured by five-choice serial reaction time behavior in nonepileptic rats. The GABA-related AEDs triazolam, phenobarbital, and chlordiazepoxide significantly disrupted performance by increasing errors of omission, whereas tiagabine, valproate, and gabapentin did not. The sodium channel blocker carbamazepine increased errors of omission at relatively high doses, whereas the sodium channel blockers phenytoin, topiramate, and lamotrigine were without significant effect. Levetiracetam had no effect on attention. The disruptions produced by triazolam, phenobarbital, chlordiazepoxide, and carbamazepine were similar in magnitude to the effects of the muscarinic cholinergic receptor antagonist scopolamine. The present results indicate that AEDs can disrupt attention, but there are differences among AEDs in the magnitude of the disruption in nonepileptic rats, with drugs that enhance GABA receptor function producing the most consistent disruption of attention.     

Effects of antiepileptic drugs on working memory as assessed by spatial alternation performance in rats

Patients with epilepsy can have impaired cognitive abilities. Many factors contribute to this impairment, including the adverse effects of antiepileptic drugs (AEDs). However, there are few systematic data on the effects of AEDs on specific cognitive domains, such as working memory. The purpose of the present study was to evaluate the effects of AEDs on working memory as measured by delayed spatial alternation behavior in nonepileptic rats. The GABA-related AEDs triazolam and phenobarbital significantly disrupted performance, whereas tiagabine, valproate, and gabapentin did not. The sodium channel blockers carbamazepine and topiramate produced modest but significant disruption of performance, whereas the effects of lamotrigine were not significant and phenytoin produced a modest but significant improvement in performance but at doses that abolished responding in some animals. Levetiracetam had no effect on working memory. In contrast, ethosuximide significantly disrupted working memory. The disruptions produced by triazolam and phenobarbital were similar in magnitude to the effects of the muscarinic antagonist scopolamine. The present results indicate that AEDs can disrupt working memory, but there are differences among AEDs in the magnitude of the disruption that do not appear to be correlated with mechanism of action.     

Psychiatric and Behavioural Disorders in Children with Epilepsy (ILAE Task Force Report): Adverse cognitive and behavioural effects of antiepileptic drugs in children

The literature was evaluated for cognitive and more general behavioural effects. We distinguished the older antiepileptic drugs (AEDs), from the newer and newest AEDs. The striking finding was the lack of information on children. From the available evidence it would appear that there may be negative cognitive effects with phenobarbital, phenytoin, topiramate and zonisamide, and adverse behavioural effects with phenobarbital, valproate, gabapentin, topiramate, levetiracetam and zonisamide. There is inconclusive data on ethosuximide, clobazam, vigabatrin, felbamate, pregabalin, stiripentol, rufinamide, lacosamide and retigabine. The following drugs appear to be neutral with regard to cognitive effects: valproate, carbamazepine, gabapentin and oxcarbazepine. Carbamazepine appears to be neutral with regard to behavioural effects. Positive cognitive effects have been reported with lamotrigine and levetiracetam. Positive behavioural effects have been reported with lamotrigine. Recommendations are provided.     

Introduction: Goals

Summary: Epilepsy is characterized by recurrent seizures. Many epilepsies with focal seizures as well as convulsive generalized seizures respond satisfactorily to antiepileptic drugs (AEDs) that reduce repetitive firing (e.g., phenytoin, carbamazepine, and valproate) or that augment GABA_A-mediated inhibition (e.g., phenobarbital and benzodiazepines). A number of drugs presently under development, such as NMDA receptor antagonists, loreclezole, losigamone, meth-ysticine, and dextromethorphan, are promising in acute animal models of otherwise drug-resistant convulsant activity. As a result of recent studies in both experimental models and surgically resected human epileptic brain, the prospects for development of AEDs have significantly improved. Several new AEDs recently have reached the commercial market or are in experimental or clinical trials. A comparative presentation of the standing of the new AEDs with respect to their efficacy and side effects is necessary, but still very difficult. Because initial experience with new AEDs is restricted to populations with severe drug-resistant epilepsy, the crucial question whether potential new AEDs can alter prognosis is not yet definitively answered. There is a clear need to compare the effects of standard AEDs and new AEDs in naive patients and over longer follow-up periods. Moreover, because of the strong desire to develop antiepileptic therapy that directly treats the primary etiology of a given epileptic syndrome , or modifies the neurobiological processes that cause recurrent seizures, better experimental epilepsy models for chronic epilepsy and further clinical studies are necessary to increase the knowledge on the pathophysiology of distinct epileptic syndromes. In this respect, studies on the differences between responders and nonresponders to a given AED treatment are extremely valuable.     

Cognitive function and anticonvulsant therapy: effect of monotherapy in epilepsy

Introduction – The effect of antiepileptic drugs (AED) on cognitive function was studied in 87 patients with epilepsy. Material and methods – Group A: (n = 52) started AED treatment (carbamazepine, oxcarbazepine, sodium-valproate, phenobarbital or phenytoin). Group B: (n = 27) had AED monotherapy withdrawn (carbamazepine or sodium-valproate). Group C: (n = 8) was switched from phenytoin to carbamazepine monotherapy. The patients were tested before and 4 months after change of the treatment. Results – In group A the test performances were in general unchanged. Patients who had their drug treatment withdrawn (group B) and the patients who were switched from phenytoin to carbamazepine (group C) improved in single tests. The predominant changes in performance seem to be due to practice effect. Conclusion – Cognitive functions are only minimally influenced by AEDs after short-term treatment whereas there is a slight improvement after discontinuation of long-term administration of carbamazepine and valproate. A lack of practice effect might be the first indicator of a negative effect of AED on cognitive function.     

Effects of antiepileptic drugs on learning as assessed by a repeated acquisition of response sequences task in rats

Patients with epilepsy can have impaired cognitive abilities. Antiepileptic drugs (AEDs) may contribute to the cognitive deficits observed in patients with epilepsy, and have been shown to induce cognitive impairments in healthy individuals. However, there are few systematic data on the effects of AEDs on specific cognitive domains. We have previously demonstrated that a number of AEDs can impair working memory and attention. The purpose of the present study was to evaluate the effects of AEDs on learning as measured by a repeated acquisition of response sequences task in nonepileptic rats. The GABA-related AEDs phenobarbital and chlordiazepoxide significantly disrupted performance by shifting the learning curve to the right and increasing errors, whereas tiagabine and valproate did not. The sodium channel blockers carbamazepine and phenytoin suppressed responding at higher doses, whereas lamotrigine shifted the learning curve to the right and increased errors, and topiramate was without significant effect. Levetiracetam also shifted the learning curve to the right and increased errors. The disruptions produced by triazolam, chlordiazepoxide, lamotrigine, and levetiracetam were qualitatively similar to the effects of the muscarinic cholinergic receptor antagonist scopolamine. The present results indicate that AEDs can impair learning, but there are differences among AEDs in the magnitude of the disruption in nonepileptic rats, with drugs that enhance GABA receptor function and some that block sodium channels producing the most consistent impairment of learning.     

Anticonvulsant Drugs, Cognitive Function, and Behavior

Summary: Healthy volunteers as well as patients wih epilepsy were studied for 2 weeks in a double-blind crossover design to determine the effect of anticonvulsant drugs on cognitive function and behavior. The healthy volunteers experienced significant deficits in performance with the four drugs examined, phenytoin, carbamazepine, sodium valproate, and clobazam. The most widespread changes were seen with phenytoin; carbamazepine, sodium valproate, and clobazam did not interfere with tests of memory function. The results of the patients' studies showed that (1) when anticonvulsants are reduced, patients receiving polytherapy improve their cognitive function; (2) patients with high serum levels of anticonvulsant drugs demonstrated more cognitive impairment than those with low levels; (3) when carbamazepine is substituted for another anticonvulsant, cognitive function is improved; and (4) in patients receiving monotherapy, high serum levels are linked to greater cognitive impairment than lower levels and the profile of changes differs between the drugs.     

Hepatic Considerations in the Use of Antiepileptic Drugs

Summary: Virtually all of the major antiepileptic drugs (AEDs) can cause hepatotoxicity, although fatal hepatic reactions are rare. The mechanisms, incidences, and risk profiles for such reactions differ from drug to drug. With carbamazepine and phenytoin, hepatotoxicity may be due to drug hypersensitivity. Although the profiles of patients at risk have not been well-defined for these two antiepileptic drugs, it would appear from reports in the literature that older adolescents and adults are at higher risk than children of developing serious or fatal hepatotoxicity. Once hepatotoxicity develops, mortality rates are 10–38% with phenytoin and 25% for carbamazepine. The risk profile for valproate fatal hepatotoxicity has been more clearly defined. Those at primary risk of fatal hepatic dysfunction are children under the age of 2 years who are receiving multiple anticonvulsants and also have significant medical problems in addition to severe epilepsy. The risk is considerably lower for patients over the age of 2 years on valproate monotherapy. In contrast to the risk profile with other AEDs, adults receiving valproate as monotherapy have the lowest risk of hepatotoxicity. Fatal hepatic dysfunction coincident with valproate may be the result of aberrant drug metabolism. Concomitant use of AEDs that induce microsomal P450 enzymes (e.g., phenytoin and phenobarbital) may enhance the production of a toxic metabolite, and hence the greater risk of hepatotoxicity with polypharmacy.