Clinical, Cognitive, and Neurophysiologic Correlates of Short-Term Treatment with Carbamazepine, Oxcarbazepine, and Levetiracetam in Healthy Volunteers

The influence of antiepileptic drugs on cognition: a comparison of levetiracetam with topiramate

Levetiracetam (LEV) and topiramate (TPM) are considered highly effective novel antiepileptic drugs (AEDs) in the treatment of focal epilepsies. To explore potential side effects, this study investigated their influence on cognitive functions comparatively by means of a standardized neuropsychological test battery assessing several cognitive domains. In this observational study, cognitive changes were explored in 30 consecutively recruited patients with focal epilepsy treated with LEV and in 21 patients treated with TPM, comparing functions assessed prior to gradual initiation and after reaching steady state of the individual target dosage. Before titration, patient groups did not differ significantly with respect to cognitive performance. Whereas the LEV group manifested no change in cognitive performance after AED titration, the TPM group worsened in the cognitive domains of cognitive speed and verbal fluency, as well as short-term memory. These findings suggest that TPM, unlike LEV, may impair frontal lobe functions. The lack of cognitive side effects related to LEV treatment may be relevant for treatment decisions.

A Comparative Pharmacokinetic Study in Healthy Volunteers of the Effect of Carbamazepine and Oxcarbazepine on Cyp3a4

PURPOSE

Carbamazepine (CBZ) and oxcarbazepine (OXCZ) are well-known inducers of drug metabolism via CYP3A4. Indirect interaction studies and clinical experience suggest that CBZ has a stronger potential in this regard than OXCZ. However this has never been subject to a direct comparative study. We performed a study in healthy volunteers to investigate the relative inductive effect of CBZ and OXCZ on CYP3A4 activity using the metabolism of quinidine as a biomarker reaction.

METHODS

Ten healthy, male volunteers participated in an open, randomized crossover study consisting of two periods separated by a 4-week wash-out period. The subjects received 1200 mg oral OXCZ daily for 17 days and 800 mg oral CBZ for 17 days. A single 200 mg oral dose of quinidine was administered at baseline and following administration of CBZ and OXCZ. Outcome parameters were the formation clearance of 3-hydroxyquinidine dose and the ratio of the AUCs of 3-hydroxyquinidine to quinidine.

RESULTS

Formation clearance of 3-hydroxyquinidine was increased by means of 89% (CI: 36-164; p=0.0022) and 181% (CI: 120-260, p<0.0001) after treatment with OXCZ and CBZ, respectively, compared to baseline. The relative inductive effect of CBZ was 46% higher than for OXCZ. AUC ratio increased by means of 161% (CI: 139-187, p<0.0001) (OXCZ) and 222% (CI: 192-257, p<0.0001) (CBZ). Quinidine Cmax decreased by means of 29% (CI: 16-40, p=0.0018) (OXCZ) and 33% (CI: 18-45, p=0.0020) (CBZ). T1/2 decreased by means of 12% (CI: 6-17, p<0.0014) (OXCZ) and 32% (CI: 25-38, p<0.0001) (CBZ). tmax was not changed in either period.

CONCLUSION

We confirm a clinically significant inductive effect of both OXCZ and CBZ. The inductive effect of CBZ was about 46% higher than that of OXCZ, a difference that may be of clinical relevance.

Is short-term memory involved in decision making? Evidence from a short-term memory patient

It is reasonable to suggest that working memory (WM; Baddeley & Hitch, 1974) is involved in decision making, as decision making is dependent on the ability to remember and update past choices and outcomes. However, contradictory results have been reported in the literature concerning the role of two of its components, namely the central executive and the phonological loop. In order to investigate the role of these components in the decision-making process, we tested a patient with intact central executive but impaired phonological loop on a laboratory decision-making task involving hypothetical gambles (gambling task, GT). When tested in a no-load condition (simple keypress task), her performance was not significantly different from that of matched controls. We also verified whether her performance would be affected differently by memory-load when compared with control subjects. The memory task (holding a string of letters in memory) loaded WM without incurring number-number interference. When the memory-load was imposed during the GT, both the patient and the controls showed a decline in performance, but the strategy they adopted differed. Possible explanations are discussed. In conclusion, our results suggest that the phonological loop is not directly involved in decision making.

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.

Distinct cognitive neurophysiologic profiles for lamotrigine and topiramate

PURPOSE

To contrast the effects of lamotrigine (LTG) and topiramate (TPM) on cognitive task-related and resting-state EEG and evoked potential (EP) measures.

METHODS

We used a double-blind, randomized, crossover design. Healthy adults (N = 29) had two 8-week periods of dose escalation, 4 weeks of drug maintenance (300 mg daily), and 4 weeks of washout. EEG was recorded during working memory (WM) tasks and resting conditions at baseline, at the end of each maintenance phase, and after final washout. RESULTS. LTG did not affect overt performance on the tasks, although it reduced EEG power in both resting and WM task conditions, most prominently in the 6- to 12-Hz frequency range, and attenuated P300 evoked-potential amplitude equally in both WM task loads. TPM slowed responses and increased errors. It also increased EEG power below 6 Hz in all conditions, and reduced the amplitude of a slow wave observed in a difficult version of the WM task.

CONCLUSIONS

The drugs produced both task-independent and task-related alterations in neurophysiologic measures. The EEG and EP changes produced by TPM are consistent with an impairment of WM, as evidenced by overt performance deficits on the behavioral tasks. By contrast, the reduction in synchronous cortical activity produced by LTG was not accompanied by cognitive impairment. It is unknown whether such effects would also be observed at lower doses, such as those that often are used in monotherapy for newly diagnosed patients.

Cognitive functioning in bipolar patients receiving lamotrigine: preliminary results

Despite the increasing use of lamotrigine (LTG) in bipolar disorder, little is known about its impact on cognition in bipolar patients. Therefore, we have evaluated 33 bipolar I and II patients on cognitive measures (verbal memory, attention, executive functions) while receiving either LTG (n = 15) or another anticonvulsant (carbamazepine or valproate; n = 18). Patients receiving LTG were generally diagnosed as having bipolar II disorder, had experienced more depressive episodes but a lesser number of hospitalizations, and had better performance than the patients receiving carbamazepine or valproate on the verbal fluency task. A moderate effect size also suggests that both groups may differ on the immediate verbal memory test (California Verbal Learning Test). These preliminary results suggest a safer neurocognitive profile of LTG on bipolar patients, as compared with other anticonvulsants.

Cognitive and memory effects of the new antiepileptic drugs

Problems with cognition are common in patients with epilepsy. A series of double-blind, randomized, crossover, healthy volunteer studies have been conducted to avoid a variety of the confounding effects on cognition such as those produced by changes in seizure frequency. All of the older AEDs produced cognitive effects compared to the non-drug conditions. The cognitive effects of several of the new AEDs are described although data are limited. Studies have demonstrated that in utero AED exposure in humans may affect cognitive development. Although the cognitive effects of AEDs are generally modest, these effects can have clinical significance. The available data suggest that some of the new AEDs have fewer effects on cognition and memory than the older AEDs, and these differences can have clinical impact.

Adverse effects of antiepileptic drugs

Adverse effects of antiepileptic drugs (AEDs) are common, can have a considerable impact on quality of life and contribute to treatment failure in up to 40% of patients. The adverse effect profiles of AEDs differ greatly and are often a determining factor in drug selection because of the similar efficacy rates shown by most AEDs. The most common adverse effects are dose dependent and reversible. Cognitive impairment is of particular concern, especially for patients who work or study. Idiosyncratic effects, such as skin rashes, and chronic effects, such as weight gain, can lead to high rates of treatment discontinuation and complicate clinical management. Nearly all conventional AEDs increase the risk of congenital malformations when taken during pregnancy, with valproate posing a potentially greater risk, whereas the potential teratogenicity of new generation AEDs is largely unknown. Most conventional AEDs have a poor record when it comes to drug interactions, largely because of their tendency to interfere with hepatic drug metabolism. Some newer AEDs have no effect on hepatic drug metabolizing enzymes and are renally excreted, resulting in a lower potential for drug interactions. However, further research is needed to confirm the apparent improvement in tolerability offered by some of the newer AEDs.

EpiTrack: tracking cognitive side effects of medication on attention and executive functions in patients with epilepsy

RATIONALE

Achievement of maximum seizure control with preservation or even improvement of patient's cognitive capabilities is the major aim of epilepsy therapy. EpiTrack is a brief screening tool for the tracking of cognitive side effects of antiepileptic drugs. Test selection was based on recent studies on the effects of topiramate on cognition and retrospective inspection of results from patients with antiepileptic drug (AED) side effects.

METHODS

The 15-minute screening tool comprises six subtests: the Trail-Making Test (parts A and B), a test of response inhibition, digit span backward, written word fluency, and a maze test. These tests were standardized in 220 healthy subjects, 100 of whom were reevaluated after 5.3 months to obtain information on reliability and practice effects. Criterion validity was determined by correlation to other neuropsychological measures. For a first clinical evaluation, the impact of epilepsy (seizures) and medication on EpiTrack scores was evaluated cross-sectionally in 184 consecutive inpatients with chronic epilepsy.

RESULTS

According to the normative data, we developed an easy scoring scheme assigning test scores on a 7-point scale. The EpiTrack is suitable for patients between 18 and 60 years of age. Age corrections were included for patients between 40 and 60 years. EpiTrack scores on subtests for both controls and patients were submitted to principal component analysis. VARIMAX rotation yielded a two-factor solution (verbal/visuo-spatial) that accounted for 63.8% of the total variance in controls. In the patient group, only one factor emerged accounting for 54.7% of variance. EpiTrack correlates with global scores of attention (r=0.85) and language (r=0.67) (P's<0.001). At a cutoff score of 25, only 2.7% of the controls were classified as impaired, while impairment was indicated in 48.4% of the patients. The score is sensitive to monthly frequency of complex partial seizures and to number of AEDs. It shows negative cognitive effects of valproate and topiramate given in mono/polytherapy.

CONCLUSION

EpiTrack is a promising 15-minute screening tool for the detection and tracking of cognitive side effects of AEDs and adverse effects of seizures in patients with epilepsy. Future application will show its value in prospective follow-up studies on AED side effects.

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.