Channel-blocking Antiepileptic Drugs Research Articles

The effect of lamotrigine and other antiepileptic drugs on respiratory rhythm generation in the pre-Bötzinger complex.

Lamotrigine and other sodium-channel blocking agents are among the most commonly used antiepileptic drugs (AEDs). Because other sodium channel blockers, such as riluzole, can severely alter respiratory rhythm generation during hypoxia, we wanted to investigate if AEDs can have similar effects. This is especially important in the context of sudden unexpected death in epilepsy (SUDEP), the major cause of death in patients suffering from therapy-resistant epilepsy. Although the mechanism of action is not entirely understood, respiratory dysfunction after generalized tonic-clonic seizures seems to play a major role. We used transverse brainstem slice preparations from neonatal and juvenile mice containing the pre-Bötzinger complex (PreBötC) and measured population as well as intracellular activity of the rhythm-generating network under normoxia and hypoxia in the presence or absence of AEDs. We found a substantial inhibition of the gasping response induced by the application of sodium channel blockers (lamotrigine and carbamazepine). In contrast, levetiracetam, an AED-modulating synaptic function, had a much smaller effect. The inhibition of gasping by lamotrigine was accompanied by a significant reduction of the persistent sodium current (INap) in PreBötC neurons. Surprisingly, the suppression of persistent sodium currents by lamotrigine did not affect the voltage-dependent bursting activity in PreBötC pacemaker neurons, but led to a hypoxia-dependent shift of the action potential rheobase in all measured PreBötC neurons. Our results contribute to the understanding of the effects of AEDs on the vital respiratory functions of the central nervous system. Moreover, our study adds further insight into sodium-dependent changes occurring during hypoxia and the contribution of cellular properties to the respiratory rhythm generation in the pre-Bötzinger complex. It raises the question of whether sodium channel blocking AEDs could, in conditions of extreme hypoxia, contribute to SUDEP, an important issue that warrants further studies.

Changes in drug load during lacosamide combination therapy: A noninterventional, observational study in German and Austrian clinical practice.

IntroductionEffects of antiepileptic drug (AED) load changes in patients with focal seizures have not been well evaluated.MethodsSP1065 (NCT01673282) was a noninterventional, prospective, observational study conducted in a clinical practice setting. Patients (aged ≥18 years) with focal seizures were enrolled within 7 days of being prescribed adjunctive lacosamide. Observation period was ~6 months. Drug load was assessed using percentage change in ratio of actual prescribed dose and World Health Organization defined daily dose (DDD) for concomitant AEDs and all AEDs (including lacosamide). Subgroups were defined for patients with at least one concomitant sodium channel–blocking AED (SCB [+]) and those without (SCB [−]).ResultsA total of 311 patients were assessed for safety, 302 for measurement of drug load, and 240 for effectiveness. Ratio of AED dose to DDD decreased for concomitant AEDs (−9.6%) and increased for all AEDs (including lacosamide; 15.5%). Median reduction in focal seizure frequency per 28 days was 100% (range: −100, 2275.8). 70.4% and 61.7% of patients had a ≥50% or ≥75% reduction in seizure frequency, respectively; 50.8% became seizure‐free. In the SCB (+) subgroup (n = 149), ratio of AED dose to DDD decreased for concomitant AEDs (−15.0%) and increased for all AEDs (10.7%). In the SCB (−) subgroup (n = 153), ratio of AED dose to DDD decreased for concomitant AEDs (−4.4%) and increased for all AEDs (20.2%). Fifty‐seven patients (18.3%) reported ADRs, most commonly dose >400 mg/d (7.1%). Seventeen patients (5.5%) had ADRs leading to discontinuation.SignificanceAddition of lacosamide resulted in reduction of concomitant AED drug load regardless of whether concomitant AEDs were SCB (+) or SCB (−). These results indicate that addition of lacosamide in patients with focal seizures could allow clinicians to withdraw or reduce the dose of less well‐tolerated or less effective AEDs.

Understanding the Cognitive Side Effects of Antiepileptic Drugs: Can Functional Imaging Be Helpful?

Effects of Carbamazepine and Lamotrigine on Functional Magnetic Resonance Imaging Cognitive Networks Xiao F, Caciagli L, Wandschneider B, Sander JW, Sidhu M, Winston G, Burdett J, Trimmel K, Hill A, Vollmar C, Vos SB, Ourselin S, Thompson PJ, Zhou D, Duncan JS, Koepp MJ. Epilepsia. 2018;59:1362-1371. doi:10.1111/epi.14448Objective: To investigate the effects of sodium channel–blocking antiepileptic drugs (AEDs) on functional magnetic resonance imaging (fMRI) language network activations in patients with focal epilepsy. Methods: In a retrospective study, we identified patients who were treated at the time of language fMRI scanning with either carbamazepine (CBZ; n = 42) or lamotrigine (LTG; n = 42), but not another sodium channel–blocking AED. We propensity-matched 42 patients taking levetiracetam (LEV) as “patient-controls” and included further 42 age- and gender-matched healthy controls. After controlling for age, age at onset of epilepsy, gender, and antiepileptic comedications, we compared verbal fluency fMRI activations between groups and out-of-scanner psychometric measures of verbal fluency. Results: Patients on CBZ performed less well on a verbal fluency tests than those taking LTG or LEV. Compared to either LEV-treated patients or controls, patients taking CBZ showed decreased activations in left inferior frontal gyrus and patients on LTG showed abnormal deactivations in frontal and parietal default mode areas. All patient groups showed fewer activations in the putamen bilaterally compared to controls. In a post hoc analysis, out-of-scanner fluency scores correlated positively with left putamen activation. Significance: Our study provides evidence of AED effects on the functional neuroanatomy of language, which might explain subtle language deficits in patients taking otherwise well-tolerated sodium channel–blocking agents. Patients on CBZ showed dysfunctional frontal activation and more pronounced impairment of performance than patients taking LTG, which was associated only with failure to deactivate task-negative networks. As previously shown for working memory, LEV treatment did not affect functional language networks.

Psychiatric side effects and antiepileptic drugs: Observations from prospective audits.

Psychiatric comorbidities are common in people with epilepsy. A retrospective study of characteristics associated with withdrawal due to psychiatric side effects was undertaken in patients with treated epilepsy participating in prospective audits with new antiepileptic drugs (AEDs). A total of 1058 treated patients with uncontrolled seizures (942 focal-onset seizures, 116 generalized genetic epilepsies [GGEs]) participated in eight prospective, observational audits from 1996 to 2014. These patients were prescribed adjunctive topiramate (n=170), levetiracetam (n=220), pregabalin (n=135), zonisamide (n=203), lacosamide (n=160), eslicarbazepine acetate (n=52), retigabine (n=64), or perampanel (n=54). Doses were titrated according to efficacy and tolerability to optimize zeizure outcomes and reduce side effects. Psychiatric comorbidities were recorded prior to and after the addition of each AED. At baseline, patients with focal-onset seizures (189 of 942; 20.1%) were statistically more likely to have psychiatric diagnoses compared to patients with GGEs (14 of 116, 12.1%; p=0.039). Following adjunctive AED treatment, neuropsychiatric adverse effects led to AED withdrawal in 1.9-16.7% of patients. Patients with a pre-treatment psychiatric history (22 of 209; 10.5%) were statistically more likely to discontinue their new AED due to psychiatric issues compared to patients with no previous psychiatric diagnosis (50 of 849; 5.9%; p=0.017). Patients receiving sodium channel blocking AEDs (4 of 212, 1.9%) were statistically less likely to develop intolerable psychiatric problems, compared to those on AEDs possessing other mechanisms of action (68 of 846, 8.0%; p=0.012). Depression was the commonest problem, leading to discontinuation of AEDs in 2.8% (n=30) patients. Aggression was statistically more common in men (11 of 527, 2.1%) compared to women (1 of 531, 0.2%; p=0.004). Patients with learning disability (12 of 122, 9.8%; p=0.0015) were statistically less likely to have psychiatric issues prior to adjunctive AED treatment compared to other patients (208 of 936, 22.2%), but there were no statistically significant differences once the new AEDs were added (8 of 122 patients with learning disability, 6.6%; 64 of 936 other patients, 6.8%). Awareness of these issues may assist clinicians in avoiding, identifying and treating psychiatric comorbidities in people with epilepsy.

The ‘Photosensitivity Model’ is (also) a model for focal (partial) seizures

The ‘Photosensitivity Model’ uses a standardized stimulation protocol of repeated intermittent photic stimulation (IPS) over a three-day period, with administration of a single dose of an investigational antiepileptic drug (AED) after a baseline IPS day in photosensitive patients, followed by a third IPS day to determine duration of effect. This ‘Photosensitivity Model’ has shown its value in the development of new AEDs. Levetiracetam (LEV), currently a first-line AED in new-onset focal epilepsies, was not effective in classical animal models, but showed dose-dependent efficacy in the human ‘Photosensitivity Model’. Nevertheless, concerns have been expressed that AEDs selectively suppressing focal seizures might not suppress generalized photoparoxysmal EEG responses (PPR), the pharmacodynamic outcome measure in the Model. Herein, the following questions have been addressed: I. Can patients with generalized epileptiform discharges, evoked by IPS, so-called PPR, have focal epilepsy (focal seizures)? II. Are the photosensitive patients with focal epilepsy, who have participated in the photosensitivity trials, non-responsive to a new AED under investigation, as compared to those with generalized epilepsies? III. Are “focal epilepsy” AEDs effective both in the ‘Photosensitivity Model’ and in real life in photosensitive patients? We performed a systematic literature review of PPR in focal seizures and focal epilepsy and we analyzed data (published and unpublished) from 20 different potential AEDs studied prospectively in the ‘Photosensitivity Model’. Finally, the PPR effects of Na+ channel-blocking AEDs (considered as the most typical AEDs for focal epilepsy) are discussed with unequivocal examples given of the focal nature of a patient’s PPR. Based on the entire data evidence, we conclude that: 1. PPRs certainly exist in focal epilepsy (17% on average); 2. Clinical signs and symptoms of PPRs can be focal and 3. PPRs can definitely be used to identify or to prove efficacy of new AEDs for patients with focal epilepsy.

Polytherapy with sodium channel-blocking antiepileptic drugs is associated with arrhythmogenic ST-T abnormality in patients with epilepsy

PurposeRecent reports have documented the appearance of Brugada-type ST elevation in cases of overdose of antiepileptic drugs (AEDs). However, little is known about changes on electrocardiographs (ECGs) during AED use at therapeutic doses. AEDs may cause Brugada-type ST elevation or J-wave-like intraventricular conduction delays through an ion channel-blocking effect. In the present study, we sought to elucidate ECG abnormalities in patients on AED therapy. MethodsThe study population consisted of 120 consecutive patients with epilepsy who continued to take AEDs and had ECGs recorded during these therapies. Their clinical background and ECGs were retrospectively analyzed. Brugada-type ST elevation was classified according to the consensus report on Brugada syndrome. A J-wave-like ECG abnormality was defined as the appearance of notching or slurring of the QRS complex (>0.1mV) in the inferior/lateral leads. ResultsOf the 120 patients, 15 (12.5%) exhibited Brugada-type ST elevation and 35 (29.2%) showed a J-wave-like ECG abnormality. Polytherapy with sodium channel-blocking AEDs (e.g., carbamazepine, phenytoin, lamotrigine) was more frequently observed in patients with Brugada-type ST elevation (p=0.048). However, the serum concentrations of these medicines did not differ between patients with and without ECG abnormalities (carbamazepine: 7.9±4.1 vs. 7.2±5.9μg/dL; phenytoin: 12.7±4.1 vs. 15.5±9.5μg/dL, NS). ConclusionST-T abnormalities were frequently seen in patients using AEDs. The presence of Brugada-type ST elevation was associated with polytherapy with sodium channel-blocking AEDs.

Inverse Association between Sodium Channel-Blocking Antiepileptic Drug Use and Cancer: Data Mining of Spontaneous Reporting and Claims Databases.

Purpose: Voltage-gated sodium channels (VGSCs) are drug targets for the treatment of epilepsy. Recently, a decreased risk of cancer associated with sodium channel-blocking antiepileptic drugs (AEDs) has become a research focus of interest. The purpose of this study was to test the hypothesis that the use of sodium channel-blocking AEDs are inversely associated with cancer, using different methodologies, algorithms, and databases.Methods: A total of 65,146,507 drug-reaction pairs from the first quarter of 2004 through the end of 2013 were downloaded from the US Food and Drug Administration Adverse Event Reporting System. The reporting odds ratio (ROR) and information component (IC) were used to detect an inverse association between AEDs and cancer. Upper limits of the 95% confidence interval (CI) of < 1 and < 0 for the ROR and IC, respectively, signified inverse associations. Furthermore, using a claims database, which contains 3 million insured persons, an event sequence symmetry analysis (ESSA) was performed to identify an inverse association between AEDs and cancer over the period of January 2005 to May 2014. The upper limit of the 95% CI of adjusted sequence ratio (ASR) < 1 signified an inverse association.Results: In the FAERS database analyses, significant inverse associations were found between sodium channel-blocking AEDs and individual cancers. In the claims database analyses, sodium channel-blocking AED use was inversely associated with diagnoses of colorectal cancer, lung cancer, gastric cancer, and hematological malignancies, with ASRs of 0.72 (95% CI: 0.60 - 0.86), 0.65 (0.51 - 0.81), 0.80 (0.65 - 0.98), and 0.50 (0.37 - 0.66), respectively. Positive associations between sodium channel-blocking AEDs and cancer were not found in the study.Conclusion: Multi-methodological approaches using different methodologies, algorithms, and databases suggest that sodium channel-blocking AED use is inversely associated with colorectal cancer, lung cancer, gastric cancer, and hematological malignancies.

Adjunctive use of ezogabine/retigabine with either traditional sodium channel blocking antiepileptic drugs (AEDs) or AEDs with other mechanisms of action: Evaluation of efficacy and tolerability

Integrated data from three double-blind, randomized, placebo-controlled trials were analyzed to evaluate the efficacy and tolerability of ezogabine (EZG; US adopted name)/retigabine (RTG; international non-proprietary name) when used in combination with ≥1 sodium channel blocking antiepileptic drug (AED), ≥1 non-sodium channel blocking AED, or ≥1 AED from both the sodium channel and non-sodium channel mechanistic groups. Efficacy and tolerability appeared to be similar across all three groups of patients.

Withdrawal of anti-epileptic medications during video EEG monitoring does not alter ECG parameters or HRV

To assess if anti-epileptic drug (AED) withdrawal/cessation results in changes in ECG parameters and/or measures of heart rate variability (HRV), in patients having VEEG monitoring, that might affect susceptibility to sudden death in epilepsy. In this study, we included 36 patients with medically refractory epilepsy undergoing continuous video-EEG-ECG monitoring in hospital for pre-surgical assessment. We recorded and analysed multiple 10-min epochs of 2-lead ECG during periods when the subjects were awake and in REM and non-REM sleep, both on admission, and after the subjects had been partially or completely weaned from their AEDs. We compared ECG parameters and measures of HRV from these recorded epochs before and after AED reduction/cessation, with each patient acting as their own comparator. Epochs measured during awake, REM, and non-REM periods were analysed separately. In addition, we analysed a subgroup of patients who had been withdrawn from Na+-channel blocking medications specifically, to analyse the effect of this particular class of AEDs in isolation. Upon AED withdrawal, we observed a small increase in heart rate and shortening of the QT interval, when subjects were awake, but no other changes in ECG parameters were detected, nor did we find changes in any measure of HRV. In addition, no significant changes were found during sleep. Similar results were found in the analysis of the subgroup of patients withdrawn from Na+-channel blocking AEDs. Our study does not support a prominent role for AEDs, and withdrawal/cessation of AEDs, in deranging cardiac physiology during video EEG monitoring in medically refractory epilepsy patients undergoing video EEG monitoring.

Drug Binding Assays do not Reveal Specific Binding of Lacosamide to Collapsin Response Mediator Protein 2 (CRMP‐2)

Lacosamide (LCM; SPM 927, Vimpat®) is an antiepileptic drug (AED) used as adjunctive treatment for adults with partial-onset seizures. LCM has a different mode of action from traditional sodium channel blocking AEDs in that it selectively enhances slow inactivation of sodium channels without affecting fast inactivation. Initial investigations suggested that LCM might have an additional mode of action by binding to the collapsin response mediator protein 2 (CRMP-2), which is further investigated here. LCM binding to native and cloned human CRMP-2 was determined using radioligand binding experiments and surface plasmon resonance measurements. No specific binding of [(3) H]LCM (free concentration 100-1450 nM) to isolated or membrane bound human CRMP-2 expressed in mammalian cell systems and bacteria was observed. Surface plasmon resonance analysis also showed that LCM, over a concentration range of 0.39-100 μM, does not specifically bind to human CRMP-2. The diverse drug binding methods employed here are well suited to detect specific binding of LCM to CRMP-2 in the micromolar range, yet the results obtained were all negative. Results of this study suggest that LCM does not specifically bind to CRMP-2.

Lacosamide Does Not Alter In Vitro Long-Term Potentiation in Mouse Hippocampal CA1 Area (P05.087)

Objective: To investigate the effects of lacosamide and topiramate in an in vitro model of long-term potentiation (LTP) induced by tetanic stimulation in the CA1 area of mouse hippocampal slices. Background Long-term potentiation (LTP) is believed to play an important role in encoding memories in neuronal networks and is a widely accepted model for synaptic plasticity, learning and memory. Several antiepileptic drugs (AEDs) induce memory deficits when tested in preclinical models at therapeutic doses. Lacosamide is an AED that differs from other sodium channel-blocking AEDs such as topiramate by selectively enhancing the slow inactivation of voltage-gated sodium (Nav) channels. Topiramate reportedly affects the cognitive performance of patients receiving chronic treatment. Design/Methods:In vitro LTP was recorded in CA1 area from adult C57 black mouse hippocampal slices. Drugs were tested at a final concentration of 100μM. LTP was studied from field excitatory post-synaptic potentials (fEPSPs) recorded in the stratum radiatum of the CA1 area and evoked by Schaeffer collaterals stimulation. LTP was induced with high frequency stimulation (tetanization; TET) at 100Hz applied once during 1s. Results: Lacosamide and topiramate do not affect basal fEPSP slope, thus indicating no effect of either drug on basal synaptic transmission. In the lacosamide- and topiramate-treated slices, TET-induced potentiation (lacosamide: 555%±65%; topiramate: 599%±53%, mean±SEM) was not different to that in the control group (546%±40%, mean±SEM) and was followed by a subsequent decay to a plateau level (fitted plateau value: lacosamide 377%±16%, topiramate 396%±13%; mean±SEM) also not different from control group (fitted plateau value 396%±8%; mean±SEM). Conclusions: This study showed that perfusion of 100μM lacosamide or of 100μM topiramate did not modify LTP recorded in CA1 from mice hippocampal slices. These results suggest that acute treatment with lacosamide or topiramate does not modify neuronal plasticity underlying memory formation in adult mice. Supported by: UCB Pharma. Disclosure: Dr. Niespodziany has received personal compensation for activities with UCB Pharma as an employee. Dr. Leclegre has received personal compensation for activities with UCB Pharmaceuticals as an employe. Dr. Wolff has received personal compensation for activities with Bial, Eisai Inc., Sepracor and UCB Pharma as a consultant.

Spontaneous epileptiform discharges in a mouse model of Alzheimer's disease are suppressed by antiepileptic drugs that block sodium channels

Previous studies have demonstrated an increased risk of epilepsy in patients with Alzheimer's disease (AD). Also, in many mouse models of AD, animals have spontaneous seizures and frequent epileptiform discharges (EDs). Abnormal function of sodium channels has been proposed to contribute to hyperexcitability in a manner suggesting that drugs that block sodium channels might exacerbate the condition. Here we addressed this question by investigating whether common antiepileptic drugs (AEDs) that block sodium channels, including carbamazepine (CBZ), phenytoin (DPH), or valproic acid (VPA) have any effect on spontaneous seizures or EDs in APdE9 mice. Mice were successively treated with vehicle, followed by CBZ (10mg/kg, t.i.d.), DPH (10mg/kg, t.i.d.), or VPA (260 mg/kg, b.i.d.) for 3d. After wash-out and new vehicle treatment, higher doses of CBZ (40 mg/kg, t.i.d.), DPH (40 mg/kg, t.i.d.), or VPA (400mg/kg, b.i.d.) were administered for 3d (DPH) or 5d (CBZ, VPA). During the entire experiment, mice were under continuous (24/7) video-EEG monitoring. Our data show that each treatment reduced the number of spontaneous electrographic EDs. VPA was the most effective by reducing the ED frequency below 50% of that at baseline in 75% of mice. Western blot analysis of the Na(v)1.1 protein levels in the ventral temporal cortex and the hippocampus did not reveal any differences between the genotypes. Under the conditions tested, sodium channel blocking AEDs suppressed epileptiform activity in APdE9 mice with increased amyloid pathology. Whether this applies to other mouse models of AD with different APP mutations and/or genetic background remains to be explored.

A Pooled Analysis of Lacosamide Clinical Trial Data Grouped by Mechanism of Action of Concomitant Antiepileptic Drugs

Lacosamide, a new antiepileptic drug (AED) with a different pharmacological action that enhances sodium channel slow inactivation, is approved for the adjunctive treatment of partial-onset seizures in adults. Previous analyses of pooled phase II/III trials have demonstrated that lacosamide provides additional efficacy when added to a broad range of AEDs. To further evaluate the efficacy and safety of lacosamide by grouping patients based upon the sodium channel-blocking properties of their concomitant AEDs. Post hoc exploratory analyses were performed on pooled data in which patients were grouped based upon inclusion or non-inclusion of at least one 'traditional' sodium channel-blocking AED (defined as carbamazepine, lamotrigine, oxcarbazepine and phenytoin derivatives) as part of their concomitant AED regimen. Data pooled from previously conducted phase II/III clinical trials of lacosamide. Adult patients with partial-onset seizures with or without secondary generalization (N = 1308). Four- to six-week Titration Phase followed by 12-week maintenance treatment with adjunctive lacosamide (Vimpat®) [200, 400 or 600 mg/day] or placebo. Efficacy variables included change in seizure frequency per 28 days and the proportion of patients experiencing a ≥50% reduction in seizure frequency (50% responder rate) from Baseline to the Maintenance Phase. The proportion of patients experiencing a ≥75% reduction in seizure frequency from Baseline to the Maintenance Phase (75% responder rate) was also assessed. Safety parameters assessed were treatment-emergent adverse events (TEAEs) and discontinuation due to TEAEs. Additional safety assessments were changes in ECG and laboratory parameters as well as vital signs (including bodyweight). Of 1308 patients in the pooled phase II/III population, the majority (82%) were using at least one 'traditional' sodium channel-blocking concomitant AED. In this subgroup of patients, adjunctive lacosamide showed significant reductions in seizure frequency (p < 0.01, all dosages) and significantly greater 50% and 75% responder rates (p < 0.01 for 400 mg/day; p < 0.01 [50% responder rate] and p < 0.05 [75% responder rate] for 600 mg/day) compared with placebo; these effects were similar to the results seen in the pooled phase II/III population. TEAEs and discontinuations due to TEAEs in this subgroup were dose related and similar to the pooled phase II/III population. In the remaining subgroup of patients, i.e. those not taking 'traditional' sodium channel-blocking AEDs as part of their concomitant AED regimen (n = 231; 18%), a pronounced, dose-related seizure reduction was observed with lacosamide (p < 0.01, 400 and 600 mg/day for median percent seizure reduction and 50% or 75% responder rates). Also in this group, incidences of TEAEs were low, and discontinuations due to TEAEs did not appear to increase with dose. Analyses of ECG, laboratory and vital signs (including bodyweight) assessments did not identify abnormalities in either subgroup that were outside of the known safety profile of lacosamide observed in the pooled phase II/III population. In this post hoc exploratory analysis, adjunctive lacosamide demonstrated significant seizure reduction over placebo regardless of the inclusion of 'traditional' sodium channel blockers in the concomitant AED regimen. Future prospective studies evaluating single AED combinations (e.g. lacosamide plus one other drug) are needed to better evaluate the potential for additive or synergistic effects of lacosamide in combination with AEDs not considered 'traditional' sodium channel blockers.

Partial epilepsy with antecedent febrile seizures and seizure aggravation by antiepileptic drugs: Associated with loss of function of Nav1.1

Generalized epilepsy with febrile seizures plus (GEFS+) and severe myoclonic epilepsy in infancy (SMEI) are associated with sodium channel α-subunit type-1 gene (SCN1A) mutations. Febrile seizures and partial seizures occur in both GEFS+ and SMEI; sporadic onset and seizure aggravation by antiepileptic drugs (AEDs) are features of SMEI. We thus searched gene mutations in isolated cases of partial epilepsy with antecedent FS (PEFS+) that showed seizure aggravations by AEDs. Genomic DNA from four patients was screened for mutations in SCN1A, SCN2A, SCN1B, and GABRG2 using denaturing high-performance liquid chromatography (dHPLC) and sequencing. Whole-cell patch clamp analysis was used to characterize biophysical properties of two newly defined mutants of Na(v) 1.1 in tsA201 cells. Two heterozygous de novo mutations of SCN1A (R946H and F1765L) were detected, which were proven to cause loss of function of Na(v) 1.1. When the functional defects of mutants reported previously are compared, it is found that all mutants from PEFS+ have features of loss of function, whereas GEFS+ shows mild dysfunction excluding loss of function, coincident with mild clinical manifestations. PEFS+ is similar to SMEI clinically with possible AED-induced seizure aggravation and biophysiologically with features of loss of function, and different from SMEI by missense mutation without changes in hydrophobicity or polarity of the residues. Isolated milder PEFS+ may associate with SCN1A mutations and loss of function of Na(v) 1.1, which may be the basis of seizure aggravation by sodium channel-blocking AEDs. This study characterized phenotypes biologically, which may be helpful in understanding the pathophysiologic basis, and further in management of the disease.

Na + channel effects of remacemide and desglycinyl-remacemide in rat cortical synaptosomes

The effects of the novel anticonvulsant, remacemide hydrochloride and its active metabolite, desglycinyl-remacemide, on veratridine-induced Na + influx in rat cortical synaptosomes were investigated and compared to established Na + channel blocking antiepileptic drugs. Remacemide and desglycinyl-remacemide reduced veratridine-stimulated Na + influx to 30.7% (IC 50=160.6 μM) and 13.2% (IC 50=85.1 μM) of control, respectively. Carbamazepine, phenytoin and lamotrigine similarly reduced Na + influx to 20.1% (IC 50=325.9 μM), 79.8% and 27.9% (IC 50=23.0 μM) of control, respectively. Resting internal Na + concentrations were significantly increased by desglycinyl-remacemide (1 and 10 μM) and, conversely, decreased by desglycinyl-remacemide and carbamazepine (both 1000 μM). These studies support previous electrophysiological investigations, which suggest that remacemide and desglycinyl-remacemide exert their antiepileptic effects, at least in part, by an inhibitory action on voltage-gated Na + channels. Desglycinyl-remacemide may have an additional action on Na + homeostasis that merits further exploration.

Clinical observations on photosensitive epilepsy : H. Gerken (Kiel, West Germany)

The ‘Photosensitivity Model’ uses a standardized stimulation protocol of repeated intermittent photic stimulation (IPS) over a three-day period, with administration of a single dose of an investigational antiepileptic drug (AED) after a baseline IPS day in photosensitive patients, followed by a third IPS day to determine duration of effect. This ‘Photosensitivity Model’ has shown its value in the development of new AEDs. Levetiracetam (LEV), currently a first-line AED in new-onset focal epilepsies, was not effective in classical animal models, but showed dose-dependent efficacy in the human ‘Photosensitivity Model’. Nevertheless, concerns have been expressed that AEDs selectively suppressing focal seizures might not suppress generalized photoparoxysmal EEG responses (PPR), the pharmacodynamic outcome measure in the Model. Herein, the following questions have been addressed: I. Can patients with generalized epileptiform discharges, evoked by IPS, so-called PPR, have focal epilepsy (focal seizures)? II. Are the photosensitive patients with focal epilepsy, who have participated in the photosensitivity trials, non-responsive to a new AED under investigation, as compared to those with generalized epilepsies? III. Are “focal epilepsy” AEDs effective both in the ‘Photosensitivity Model’ and in real life in photosensitive patients? We performed a systematic literature review of PPR in focal seizures and focal epilepsy and we analyzed data (published and unpublished) from 20 different potential AEDs studied prospectively in the ‘Photosensitivity Model’. Finally, the PPR effects of Na+ channel-blocking AEDs (considered as the most typical AEDs for focal epilepsy) are discussed with unequivocal examples given of the focal nature of a patient’s PPR. Based on the entire data evidence, we conclude that: 1. PPRs certainly exist in focal epilepsy (17% on average); 2. Clinical signs and symptoms of PPRs can be focal and 3. PPRs can definitely be used to identify or to prove efficacy of new AEDs for patients with focal epilepsy.