Inhibition of glutamate release by BIA 2-093 and BIA 2-024, two novel derivatives of carbamazepine, due to blockade of sodium but not calcium channels

Treatment and care of women with epilepsy before, during, and after pregnancy: a practical guide

Women with epilepsy (WWE) wishing for a child represent a highly relevant subgroup of epilepsy patients. The treating epileptologist needs to delineate the epilepsy syndrome and choose the appropriate anti-seizure medication (ASM) considering the main goal of seizure freedom, teratogenic risks, changes in drug metabolism during pregnancy and postpartum, demanding for up-titration during and down-titration after pregnancy. Folic acid or vitamin K supplements and breastfeeding are also discussed in this review. Lamotrigine and levetiracetam have the lowest teratogenic potential. Data on teratogenic risks are also favorable for oxcarbazepine, whereas topiramate tends to have an unfavorable profile. Valproate needs special emphasis. It is most effective in generalized seizures but should be avoided whenever possible due to its teratogenic effects and the negative impact on neuropsychological development of in utero-exposed children. Valproate still has its justification in patients not achieving seizure freedom with other ASMs or if a woman decides to or cannot become pregnant for any reason. When valproate is the most appropriate treatment option, the patient and caregiver must be fully informed of the risks associated with its use during pregnancies. Folate supplementation is recommended to reduce the risk of major congenital malformations. However, there is insufficient information to address the optimal dose and it is unclear whether higher doses offer greater protection. There is currently no general recommendation for a peripartum vitamin K prophylaxis. During pregnancy most ASMs (e.g. lamotrigine, oxcarbazepine, and levetiracetam) need to be increased to compensate for the decline in serum levels; exceptions are valproate and carbamazepine. Postpartum, baseline levels are reached relatively fast, and down-titration is performed empirically. Many ASMs in monotherapy are (moderately) safe for breastfeeding and women should be encouraged to do so. This review provides a practically oriented overview of the complex management of WWE before, during, and after pregnancy.

Excitatory and inhibitory synaptic dysfunction in mania: an emerging hypothesis from animal model studies

Bipolar disorder (BD) is a common psychiatric disorder characterized by recurrent mood swings between depression and mania, and is associated with high treatment costs. The existence of manic episodes is the defining feature of BD, during which period, patients experience extreme elevation in activity, energy, and mood, with changes in sleep patterns that together severely impair their ability to function in daily life. Despite some limitations in recapitulating the complex features of human disease, several rodent models of mania have been generated and characterized, which have provided important insights toward understanding its underlying pathogenic mechanisms. Among the mechanisms, neuronal excitatory and inhibitory (E/I) synaptic dysfunction in some brain regions, including the frontal cortex, hippocampus, and striatum, is an emerging hypothesis explaining mania. In this review, we highlight recent studies of rodent manic models having impairments in the E/I synaptic development and function. We also summarize the molecular and functional changes of E/I synapses by some mood stabilizers that may contribute to the therapeutic efficacy of drugs. Furthermore, we discuss potential future directions in the study of this emerging hypothesis to better connect the outcomes of basic research to the treatment of patients with this devastating mental illness.

Studies in rodents offer insights into bipolar disorder that may help understanding and treatment of this common and debilitating condition. Kihoon Han and colleagues at Korea University in Seoul review research using mice and rats to model the episodes of mania in patients with bipolar disorder. The research supports an emerging hypothesis implicating specific problems with nervous transmission in the brain in the onset of mania. The hypothesis suggests that the transmission of signals between particular nerve cells whose normal function is either to excite or to inhibit other nerve cells may be involved. It also indicates regions of the brain most involved in manic episodes. Changes at the affected nerve junctions—called synapses—brought about by mood-stabilizing drugs are examined. The hypothesis suggests new approaches to treatment options for researchers to explore.

An Updated Overview on Therapeutic Drug Monitoring of Recent Antiepileptic Drugs

Given the distinctive characteristics of both epilepsy and antiepileptic drugs (AEDs), therapeutic drug monitoring (TDM) can make a significant contribution to the field of epilepsy. The measurement and interpretation of serum drug concentrations can be of benefit in the treatment of uncontrollable seizures and in cases of clinical toxicity; it can aid in the individualization of therapy and in adjusting for variable or nonlinear pharmacokinetics; and can be useful in special populations such as pregnancy. This review examines the potential for TDM of newer AEDs such as eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, perampanel, pregabalin, rufinamide, retigabine, stiripentol, tiagabine, topiramate, vigabatrin, and zonisamide. We describe the relationships between serum drug concentration, clinical effect, and adverse drug reactions for each AED as well as the different analytical methods used for serum drug quantification. We discuss retrospective studies and prospective data on the serum drug concentration-efficacy of these drugs and present the pharmacokinetic parameters, oral bioavailability, reference concentration range, and active metabolites of newer AEDs. Limited data are available for recent AEDs, and we discuss the connection between drug concentrations in terms of clinical efficacy and nonresponse. Although we do not propose routine TDM, serum drug measurement can play a beneficial role in patient management and treatment individualization. Standardized studies designed to assess, in particular, concentration-efficacy-toxicity relationships for recent AEDs are urgently required.

Eslicarbazepine acetate: a review of its use as adjunctive therapy in refractory partial-onset seizures

Eslicarbazepine acetate (Aptiom(®), Zebinix(®)) is approved for the adjunctive treatment of partial-onset seizures in adults aged ≥18 years. Adjunctive therapy with oral eslicarbazepine acetate 800 or 1,200 mg once daily was associated with a significantly lower standardized seizure frequency (primary endpoint) than placebo in patients aged ≥18 years with refractory partial-onset seizures in three, randomized, double-blind, multinational, phase III trials. In a fourth randomized, double-blind, multinational, phase III trial in patients aged ≥16 years with refractory partial-onset seizures, adjunctive eslicarbazepine acetate 1,200 mg once daily, but not 800 mg once daily, was associated with a significantly lower standardized seizure frequency (primary endpoint). Responder rates were significantly higher with eslicarbazepine acetate 1,200 mg once daily than with placebo in these four trials, and with eslicarbazepine acetate 800 mg once daily than with placebo in two trials. The efficacy of eslicarbazepine acetate was maintained in the longer term, according to the results of 1-year extension studies. Adjunctive therapy with oral eslicarbazepine acetate was generally well tolerated in patients with refractory partial-onset seizures, with most adverse events being of mild to moderate severity. In conclusion, eslicarbazepine acetate is a useful option for the adjunctive treatment of patients with refractory partial-onset seizures.

Advances in anti-epileptic drug testing

In the past twenty-one years, 17 new antiepileptic drugs have been approved for use in the United States and/or Europe. These drugs are clobazam, ezogabine (retigabine), eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, perampanel, pregabalin, rufinamide, stiripentol, tiagabine, topiramate, vigabatrin and zonisamide. Therapeutic drug monitoring is often used in the clinical dosing of the newer anti-epileptic drugs. The drugs with the best justifications for drug monitoring are lamotrigine, levetiracetam, oxcarbazepine, stiripentol, and zonisamide. Perampanel, stiripentol and tiagabine are strongly bound to serum proteins and are candidates for monitoring of the free drug fractions. Alternative specimens for therapeutic drug monitoring are saliva and dried blood spots. Therapeutic drug monitoring of the new antiepileptic drugs is discussed here for managing patients with epilepsy.

Safety, Tolerability, and Pharmacokinetic Profile of BIA 2-093, a Novel Putative Antiepileptic, in a Rising Multiple-Dose Study in Young Healthy Humans

This was a double-blind, randomized, placebo-controlled study to investigate rising oral doses of BIA 2-093 (S-(-)-10-acetoxy-10,11-dihydro-5H-dibenz/b,f/azepine-5-carboxamide), a putative new antiepileptic drug. Within each of 4 dosage groups of 8 healthy male adult subjects, 2 subjects were randomized to receive placebo, and the remaining 6 subjects were randomized to receive BIA 2-093 (200 mg bid, 400 mg qd, 800 mg qd, and 1200 mg qd) for 8 days. Concentrations of BIA 2-093 in plasma or urine were generally not measurable. Median maximum plasma concentrations of the major metabolite (licarbazepine, (+/-)-10,11-dihydro-10-hydroxy-5H-dibenz/b,f/azepine-5-carboxamide) were attained (t(max)) at 2 to 3 h postdose; thereafter, plasma concentrations declined with a mean apparent terminal half-life of 9 to 13 h following repeated dosing. The extent of systemic exposure to licarbazepine increased in an approximately dose-proportional manner following single and repeated administration. Licarbazepine accumulated in plasma following repeated administration of BIA 2-093; the mean extent of accumulation (R(O), calculated from AUC(0-tau) (day 8)/AUC(0-tau) (day 1)) was 3.0 after repeated, twice-daily dosing and 1.4 to 1.7 after once-daily dosing. Steady-state plasma licarbazepine concentrations were attained at 4 to 5 days of once- or twice-daily dosing, consistent with an effective half-life on the order of 20 to 24 h. The mean renal clearance of licarbazepine from plasma was approximately 20 to 30 mL/min, which is low compared with the glomerular filtration rate. The total amount of licarbazepine recovered in urine was approximately 20% within 12 h postdose and 40% within 24 h postdose. All adverse events were mild in severity, except for 1 case of somnolence of moderate severity, which occurred in a subject receiving 1200 mg BIA 2-093. The incidence of adverse events was similar between all treatment groups, including placebo. There were no serious adverse events. In conclusion, BIA 2-093 was well tolerated and appeared to be rapidly and extensively metabolized to licarbazepine following single and repeated administration to healthy young subjects.

Pharmacotherapy of the third-generation AEDs: lacosamide, retigabine and eslicarbazepine acetate

INTRODUCTION

The search for new, more effective antiepileptic drugs (AEDs) continues. The three most recently approved drugs, the so-called third-generation AEDs, include lacosamide, retigabine and eslicarbazepine acetate and are licensed as adjunctive treatment of partial epilepsy in adults.

AREAS COVERED

For the above three AEDs, their mechanisms of action, pharmacokinetic characteristics, drug-drug interactions, pharmacotherapeutics, dose and administration and therapeutic drug monitoring are reviewed in this paper.

EXPERT OPINION

Lacosamide and retigabine act through novel mechanisms, while eslicarbazepine acetate, a pro-drug for eslicarbazepine, acts in a similar manner to several other AEDs. All three AEDs are associated with linear pharmacokinetic and rapid absorption and undergo metabolism. Their drug-drug interaction profile is low (lacosamide and retigabine) to modest (eslicarbazepine) in propensity. At the highest approved doses for the three AEDs, responder rates were similar. The most commonly observed adverse effects compared with placebo were dizziness, headache, diplopia and nausea for lacosamide; dizziness, somnolence and fatigue for retigabine and dizziness and somnolence for eslicarbazepine acetate. The precise role that these new AEDs will have in the treatment of epilepsy and whether they will make a significant impact on the prognosis of intractable epilepsy is not yet known and will have to await further clinical experience.

A review of eslicarbazepine acetate for the adjunctive treatment of partial-onset epilepsy

Eslicarbazepine acetate (ESL) is a novel antiepileptic drug indicated for the treatment of partial-onset seizures. Structurally, it belongs to the dibenzazepine family and is closely related to carbamazepine and oxcarbazepine. Its main mechanism of action is by blocking the voltage-gated sodium channel. ESL is a pro-drug that is rapidly metabolized almost exclusively into S-licarbazepine, the biologically active drug. It has a favorable pharmacokinetic and drug-drug interaction profile. However, it may induce the metabolism of oral contraceptives and should be used with caution in females of child-bearing age. In the pre-marketing placebo-controlled clinical trials ESL has proven effective as adjunctive therapy in adult patients with refractory of partial-onset seizures. Best results were observed on a single daily dose between 800 and 1200 mg. In general, ESL was well tolerated, with most common dose-related side effects including dizziness, somnolence, headache, nausea and vomiting. Hyponatremia has been observed (0.6%–1.3%), but the incidence appears to be lower than with the use of oxcarbazepine. There is very limited information on the use of ESL in children or as monotherapy.

Therapeutic Drug Monitoring of the Newer Anti-Epilepsy Medications

In the past twenty years, 14 new antiepileptic drugs have been approved for use in the United States and/or Europe. These drugs are eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, pregabalin, rufinamide, stiripentol, tiagabine, topiramate, vigabatrin and zonisamide. In general, the clinical utility of therapeutic drug monitoring has not been established in clinical trials for these new anticonvulsants, and clear guidelines for drug monitoring have yet to be defined. The antiepileptic drugs with the strongest justifications for drug monitoring are lamotrigine, oxcarbazepine, stiripentol, and zonisamide. Stiripentol and tiagabine are strongly protein bound and are candidates for free drug monitoring. Therapeutic drug monitoring has lower utility for gabapentin, pregabalin, and vigabatrin. Measurement of salivary drug concentrations has potential utility for therapeutic drug monitoring of lamotrigine, levetiracetam, and topiramate. Therapeutic drug monitoring of the new antiepileptic drugs will be discussed in managing patients with epilepsy.

Therapeutic Drug Monitoring of the Newer Anti-Epilepsy Medications

In the past twenty years, 14 new antiepileptic drugs have been approved for use in the United States and/or Europe. These drugs are eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, pregabalin, rufinamide, stiripentol, tiagabine, topiramate, vigabatrin and zonisamide. In general, the clinical utility of therapeutic drug monitoring has not been established in clinical trials for these new anticonvulsants, and clear guidelines for drug monitoring have yet to be defined. The antiepileptic drugs with the strongest justifications for drug monitoring are lamotrigine, oxcarbazepine, stiripentol, and zonisamide. Stiripentol and tiagabine are strongly protein bound and are candidates for free drug monitoring. Therapeutic drug monitoring has lower utility for gabapentin, pregabalin, and vigabatrin. Measurement of salivary drug concentrations has potential utility for therapeutic drug monitoring of lamotrigine, levetiracetam, and topiramate. Therapeutic drug monitoring of the new antiepileptic drugs will be discussed in managing patients with epilepsy.

Eslicarbazepine acetate: a new option for the treatment of focal epilepsy

BACKGROUND

Epilepsy is a neurological condition with an increased probability of seizure occurrence through time. Although many anti-epileptic drugs (AEDs) exist, they fail to treat seizures in 30% of patients with epilepsy. For these patients, new AEDs potentially more efficacious and safe are developed.

OBJECTIVE

To evaluate the effectiveness of eslicarbazepine acetate (ESL) in the treatment of patients with refractory epilepsy.

METHODS

A review of the literature was carried out using PubMed central. A direct contact with the drug manufacturer and developer was made.

RESULTS/CONCLUSION

ESL is an AED that acts by inhibiting voltage-gated sodium channels. It has proved efficacious in the treatment of patients with refractory focal-onset epilepsy with a good safety profile. Evaluation of its use for treating other epileptic syndromes and its role as an initial treatment option for patients with epilepsy is warranted.

Eslicarbazepine acetate

Eslicarbazepine acetate, a prodrug of eslicarbazepine (S-licarbazepine), is a novel, voltage-gated sodium channel antagonist under development for the adjunctive treatment of adult patients experiencing treatment-refractory partial-onset seizures. * In phase III trials, eslicarbazepine acetate 800 and 1200 mg once daily significantly reduced seizure frequency compared with placebo over 12 weeks of maintenance treatment in adults experiencing partial-onset seizures who were taking 1-3 concomitant antiepileptic drugs. * During long-term, open-label treatment for up to 1 year, eslicarbazepine acetate at a median dosage of 800 mg once daily produced sustained reductions from baseline in seizure frequency. * Long-term treatment with eslicarbazepine acetate significantly improved from baseline health-related quality of life as assessed by the Quality-of-Life in Epilepsy Inventory-31 instrument. Similarly, eslicarbazepine acetate significantly reduced depressive symptoms assessed by the Montgomery-Asberg Depression Rating Scale. * Eslicarbazepine acetate was generally well tolerated in clinical trials. The majority of treatment-emergent adverse events were of mild to moderate severity and most occurred early in treatment.

Drug assessment based on detection of L-glutamate released from C6 glioma cells using an enzyme-luminescence method

Monitoring of excitation activity of nerve cells is very useful for not only brain research but also assessment of the effects of various chemicals, including drugs and toxins. We previously reported a novel enzyme-luminescence method for real-time monitoring of l-glutamate release from C6 glioma cells with high levels of sensitivity ( approximately 10 nM) and temporal resolution (<1 s) using a luminescence plate reader. In the present study, we tested the applicability of this novel system for assessment of effects of drugs in vitro. Several drugs (e.g., veratridine and 4-aminopyridine) were administered to C6 glioma cells for inducing glutamate release. Moreover, antagonists of voltage-dependent Ca (2+) channels (e.g., nifedipine, flunarizine, and NiCl 2) and Na (+) channels (e.g., carbamazepine and lidocaine) were applied separately for evaluating the effects of these chemicals on glutamate release from the cells. The combined effect of carbamazepine and lidocaine was also investigated by using our method, and the combined effect was found to be more potent than that of single drug administration. These results indicated that the glutamate release from C6 cells was modulated by these drugs in a way similar to that found by using several conventional analytical techniques. We therefore conclude that the developed monitoring system for real-time detection of dynamic l-glutamate release from cells could be very useful for application to assessment of drugs acting on the nervous system.

Effect of eslicarbazepine acetate (BIA 2-093) on latrunculin A-induced seizures and extracellular amino acid concentrations in the rat hippocampus

PURPOSE

Eslicarbazepine acetate (ESL, BIA 2-093) is a novel antiepileptic drug endowed with an anticonvulsant potency similar to that of carbamazepine, and shares with carbamazepine and oxcarbazepine the capability to inhibit voltage-gated sodium channels. ESL is efficacious against maximal electroshock seizure-induced seizures, protects against picrotoxin-induced seizures in mice and rats, and prevents development of kindling in rats. In vivo, latrunculin A microperfusion in the rat hippocampus induces acute epileptic seizures and long-term biochemical changes leading to decreased picrotoxin seizure threshold and spontaneous seizures. We have tested the effect of ESL on latrunculin A-induced seizures, and its effect on the changes in extracellular amino acid levels induced by latrunculin A.

METHODS

Rat hippocampus was continuously perfused with a latrunculin A solution (4 microM) through CMA/12 microdialysis probes at a flow rate of 2 microl/min during 8 h with continuous EEG and videotape recording for 3 consecutive days. The same protocol was repeated after oral administration of ESL (3, 10 and 30 mg/kg). Samples from the microdialysate were collected and analyzed by HPLC using pre-column derivatization with 6 aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC) and fluorescence detection.

RESULTS

After the administration of 3 mg/kg of ESL, seizures were completely suppressed in the 66.7% of the rats. 10 and 30 mg/kg of ESL did completely suppressed seizures in the 100% of the animals studied. Hippocampal extracellular levels of glutamate, glycine and aspartate were significantly increased during latrunculin A microperfusion, while GABA levels remained unchanged. At the doses studied, ESL reversed the increases in extracellular glutamate and aspartate concentrations to basal levels and significantly reduced glycine levels.

CONCLUSIONS

ESL, at oral doses of 3, 10 and 30 mg/kg, shows an excellent anticonvulsant effect against seizures induced by latrunculin A microperfusion in the rat, and prevents the increases in glutamate and aspartate induced by latrunculin A.

Eslicarbazepine Acetate: A Double-blind, Add-on, Placebo-controlled Exploratory Trial in Adult Patients with Partial-onset Seizures

OBJECTIVE

To explore the efficacy and safety of eslicarbazepine acetate (BIA 2-093), a new antiepileptic drug, as adjunctive therapy in adult patients with partial epilepsy.

METHODS

A multicenter, double-blind, randomized, placebo-controlled study was conducted in 143 refractory patients aged 18-65 years with >or=4 partial-onset seizures/month. The study consisted of a 12-week treatment period followed by a 1-week tapering off. Patients were randomly assigned to one of three groups: treatment with eslicarbazepine acetate once daily (QD, n=50), twice daily (BID, n=46), or placebo (PL, n=47). The daily dose was titrated from 400 mg to 800 mg and to 1,200 mg at 4-week intervals. The proportion of responders (patients with a >or=50% seizure reduction) was the primary end point.

RESULTS

The percentage of responders versus baseline showed a statistically significant difference between QD and PL groups (54% vs. 28%; 90% CI =-infinity, -14; p=0.008). The difference between the BID (41%) and PL did not reach statistical significance (90% CI =-infinity, -1; p=0.12). A significantly higher proportion of responders in weeks 5-8 was found in the QD group than in the BID group (58% vs. 33%, respectively, p=0.022). At the end of the 12-week treatment, the number of seizure-free patients in the QD and BID groups was 24%, which was significantly different from the PL group. The incidence of adverse events was similar between the treatment groups and no drug-related serious adverse events occurred.

CONCLUSION

Eslicarbazepine acetate was efficacious and well tolerated as an adjunctive therapy of refractory epileptic patients.

Eslicarbazepine acetate (BIA 2-093)

Eslicarbazepine acetate (ESL) [(S)-(--)-10-acetoxy-10,11-dihydro-5H-dibenz[b,f]azepine-5-carboxamide], formerly known as BIA 2-093, is a novel central nervous system (CNS)-active compound with anticonvulsant activity. It behaves as a voltage-gated sodium channel (VGSC) blocker and is currently under clinical development for the treatment of epilepsy and bipolar disorder. ESL shares with carbamazepine and oxcarbazepine the dibenzazepine nucleus bearing the 5-carboxamide substitute, but is structurally different at the 10,11-position. This molecular variation results in differences in metabolism, preventing the formation of toxic epoxide metabolites such as carbamazepine-10,11 epoxide. In pharmacokinetic studies in humans, ESL was rapidly and extensively metabolized to eslicarbazepine (S-licarbazepine), which is responsible for pharmacological activity. ESL has been tested in patients with refractory partial-onset seizures and was found to be efficacious and well tolerated. Monotherapy studies in adult epileptic patients and add-on studies in epileptic children are in the planning process. The efficacy and safety data appear to be very promising considering the refractory nature of the epileptic population enrolled in studies to date. Results of ongoing phase III studies in adult epileptic patients are expected to be available in 2007 and are required to define the position of ESL in the therapy of patients with epilepsy.

Anticonvulsant effect of eslicarbazepine acetate (BIA 2-093) on seizures induced by microperfusion of picrotoxin in the hippocampus of freely moving rats

Eslicarbazepine acetate (BIA 2-093, S-(-)-10-acetoxy-10,11-dihydro-5H-dibenzo/b,f/azepine-5-carboxamide) is a novel antiepileptic drug, now in Phase III clinical trials, designed with the aim of improving efficacy and safety in comparison with the structurally related drugs carbamazepine (CBZ) and oxcarbazepine (OXC). We have studied the effects of oral treatment with eslicarbazepine acetate on a whole-animal model in which partial seizures can be elicited repeatedly on different days without changes in threshold or seizure patterns. In the animals treated with threshold doses of picrotoxin, the average number of seizures was 2.3+/-1.2, and average seizure duration was 39.5+/-8.4s. Pre-treatment with a dose of 30 mg/kg 2h before picrotoxin microperfusion prevented seizures in the 75% of the rats. Lower doses (3 and 10mg/kg) did not suppress seizures, however, after administration of 10mg/kg, significant reductions in seizures duration (24.3+/-6.8s) and seizure number (1.6+/-0.34) were found. No adverse effects of eslicarbazepine acetate were observed in the behavioral/EEG patterns studied, including sleep/wakefulness cycle, at the doses studied.

Single and combined effects of carbamazepine and vinpocetine on depolarization-induced changes in Na+, Ca2+ and glutamate release in hippocampal isolated nerve endings

The single and combined effects of carbamazepine and vinpocetine on the release of the excitatory amino acid neurotransmitter glutamate, on the rise in internal Na+ (Na(i), as determined with SBFI), and on the rise in internal Ca2+ (Ca(i), as determined with fura-2) induced by an increased permeability of presynaptic Na+ channels, with veratridine, or by an increased permeability of presynaptic Ca2+ channels with high K+, were investigated in isolated hippocampal nerve endings. The present study shows that carbamazepine and vinpocetine, both inhibit dose dependently the release of preloaded [3H]Glu induced by veratridine. However, carbamazepine is two orders of magnitude less potent than vinpocetine. The calculated IC(50)'s for carbamazepine and vinpocetine to inhibit veratridine-induced [3H]Glu release are 200 and 2 microM, respectively. Consistently 150 microM carbamazepine and 1.5 microM vinpocetine reduce the veratridine-induced rise in Na(i) in a similar extent. The single effects of carbamazepine and of vinpocetine on the presynaptic Na+ channel mediated responses, namely the rise in Na(i) and the release of Glu induced by veratridine, are additive. Responses that depend on the entrance of external Ca2+ via presynaptic Ca2+ channels, such as the release of [3H]Glu and the rise in Ca(i) induced by high K+, are insensitive to 300 microM carbamazepine and slightly reduced by 5 microM vinpocetine. It is concluded that the additive effects of carbamazepine, which is one of the most common antiepileptic drugs, and vinpocetine that besides its known neuroprotective action and antiepileptic potential is a memory enhancer, may perhaps be advantageous in the treatment of epileptic patients.

Diverse mechanisms of antiepileptic drugs in the development pipeline

There is a remarkable array of new chemical entities in the current antiepileptic drug (AED) development pipeline. In some cases, the compounds were synthesized in an attempt improve upon the activity of marketed AEDs. In other cases, the discovery of antiepileptic potential was largely serendipitous. Entry into the pipeline begins with the demonstration of activity in one or more animal screening models. Results from testing in a panel of such models provide a basis to differentiate agents and may offer clues as to the mechanism. Target activity may then be defined through cell-based studies, often years after the initial identification of activity. Some pipeline compounds are believed to act through conventional targets, whereas others are structurally novel and may act by novel mechanisms. Follow-on agents include the levetiracetam analogs brivaracetam and seletracetam that act as SV2A-ligands; the valproate-like agents valrocemide, valnoctamide, propylisopropyl acetamide, and isovaleramide; the felbamate analog flurofelbamate, a dicarbamate, and the unrelated carbamate RWJ-333369; the oxcarbazepine analog licarbazepine, which probably acts as a use-dependent sodium channel blockers, and its prodrug acetate BIA 2-093; various selective partial benzodiazepine receptor agonists, including ELB139, which is a positive allosteric modulator of alpha3-containing GABA(A) receptors. A variety of AEDs that may act through novel targets are also in clinical development: lacosamide, a functionalized amino acid; talampanel, a 2,3-benzodiazepine selective noncompetitive AMPA receptor antagonist; NS1209, a competitive AMPA receptor antagonist; ganaxolone, a neuroactive steroid that acts as a positive modulator of GABA(A) receptors; retigabine, a KCNQ potassium channel opener with activity as a GABA(A) receptor positive modulator; the benzanilide KCNQ potassium channel opener ICA-27243 that is more selective than retigabine; and rufinamide, a triazole of unknown mechanism.

The suppressive effects of oxcarbazepine on mechanical and cold allodynia in a rat model of neuropathic pain

Oxcarbazepine (OCBZ) is a keto analog of carbamazepine (CBZ) and may have similar analgesic properties to CBZ, but studies on its effects in neuropathic pain conditions are rare. In this study, we evaluated the analgesic effects of OCBZ in a rat neuropathic pain model. Male Sprague-Dawley rats were prepared by tightly ligating the left L5 and L6 spinal nerves to produce neuropathic pain. Sixty neuropathic rats were randomly assigned into six groups, and normal saline, a vehicle (polyethylene glycol 400), and OCBZ (10 mg/kg, 20 mg/kg, 30 mg/kg, and 50 mg/kg) were intraperitoneally administered to these individual groups. Mechanical and cold allodynia were observed at preadministration and 15, 30, 60, 90, 120, 150, and 180 min after drug administration and were quantified by measuring withdrawal frequencies to stimuli with von Frey filaments and 100% acetone, respectively. Rotarod performance was measured to detect drug-induced adverse motor effects. In the OCBZ-treated groups, withdrawal frequencies to mechanical and cold stimuli were significantly reduced in a dose-dependent manner (P < 0.05). Only at the largest dose did OCBZ reduce rotarod performance time. These results suggest that OCBZ may be a possible therapeutic consideration in neuropathic pain conditions associated with allodynia and hyperalgesia.

Differential Effects of Neuropathic Analgesics on Wind-up-like Pain and Somatosensory Function in Healthy Volunteers

OBJECTIVES

To investigate the effects of gabapentin, carbamazepine, and amitriptyline on temporal summation, simple nociceptive pain, and innocuous touch sensation in healthy volunteers.

METHODS

A placebo controlled four-way crossover double-blind randomized protocol was followed. Seventeen healthy subjects, male and female, aged 18 to 24, took part. Punctate pain, temporal summation pain to repeat punctate stimulation, and vibration detection threshold were assessed in triplicate. Study drugs were given as bedtime and early morning doses with assessments carried out midmorning.

RESULTS

Gabapentin and carbamazepine significantly reduced the intensity of temporal summation pain (P < 0.001 and P < 0.01 respectively), whereas amitriptyline significantly increased temporal summation pain (P < 0.001). None of the drugs affected pain produced by a single punctate stimulus (P > 0.05). Carbamazepine increased vibration detection thresholds (P < 0.05), but neither gabapentin nor amitriptyline had any detectable effect on vibration.

DISCUSSION

We have shown that gabapentin, carbamazepine, and amitriptyline, three pharmacologically different drugs, have distinct and quantifiable effects on somatosensory pathways in healthy volunteers. These findings provide a link between pharmacology of the study drugs and clinical effectiveness. The effects of gabapentin and carbamazepine on temporal summation pain show that these drugs can block centrally amplified wind-up pain in the absence of a neuropathic disorder.

Progress report on new antiepileptic drugs: a summary of the Seventh Eilat Conference (EILAT VII)

The Seventh Eilat Conference on New Antiepileptic Drugs (AEDs) (EILAT VII) took place in Villasimius, Sardinia, Italy from the 9th to 13th May 2004. Basic scientists, clinical pharmacologists and neurologists from 24 countries attended the conference,whose main themes included advances in pathophysiology of drug resistance, new AEDs in pediatric epilepsy syndromes, modes of AED action and spectrum of adverse effects and a re-appraisal of comparative responses to AED combinations. Consistent with previous formats of this conference, the central part of the conference was devoted to a review of AEDs in development, as well as updates on second-generation AEDs. This article summarizes the information presented on drugs in development, including atipamezole, BIA-2-093, fluorofelbamate, NPS 1776, pregabalin, retigabine, safinamide, SPM 927, stiripentol, talampanel,ucb 34714 and valrocemide (TV 1901). Updates on felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine,topiramate, vigabatrin, zonisamide, new oral and parenteral formulations of valproic acid and SPM 927 and the antiepileptic vagal stimulator device are also presented.

Safety, tolerability and pharmacokinetic profile of BIA 2-093, a novel putative antiepileptic agent, during first administration to humans

OBJECTIVE

To evaluate the safety, tolerability, pharmacokinetics and pharmacodynamics of BIA 2-093 [S-(-)-10-acetoxy-10,11-dihydro-5H-dibenzo/b,f/aze- pine-5-carboxamide] in healthy male volunteers.

DESIGN

This was a double-blind, randomised, placebo-controlled, single ascending dose study performed with BIA 2-093, a new putative antiepileptic drug.

PARTICIPANTS AND METHODS

Groups of eight healthy male subjects (two randomised to receive placebo and the remaining six to receive BIA 2-093) received single oral doses of BIA 2-093 of 20, 50, 100, 200, 400, 600, 900 and 1200 mg. A total of 64 healthy male volunteers aged 18-35 years participated in the study.

RESULTS

The incidence of adverse events, which were mild in severity, was similar between all treatment groups, including the placebo group. There were no serious adverse events during this study. No clinically significant abnormalities in laboratory safety tests, vital signs, weight, physical examination or ECG were reported. BIA 2-093 appeared to be rapidly and extensively metabolised to BIA 2-005 [RS(+/-)-10,11-dihydro-10-hydroxy-5H-dibenzo/b,f/azepine-5-carboxamide], the major metabolite, and oxcarbazepine (the minor metabolite), following single oral doses of BIA 2-093 of 20-1200 mg. Plasma BIA 2-093 concentrations were generally below the limit of quantification of the assay. Maximum plasma concentrations (C(max)) of BIA 2-005 and oxcarbazepine were reached, respectively, at 0.75-4h and 6h postdose, after which they declined with an approximate mean apparent terminal half-life of 8-17h and 7-12h, respectively. The increase in systemic exposure to BIA 2-005 was approximately proportional to the administered dose for C(max) and greater than dose proportional for the area under the concentration-time curve. Renal clearance of BIA 2-005 (20 mL/min) appeared to be constant over the dose range studied, indicating that the dose-dependent urinary recovery was due either to increased formation of BIA 2-005 with increasing dose level or to decreased non-renal elimination of the metabolite.

CONCLUSIONS

BIA 2-093 undergoes extensive metabolism to BIA 2-005 and was well tolerated at oral doses of 20-1200 mg.The results provide a basis for further clinical trials with BIA 2-093.

Regulation of vesicle traffic and neurotransmitter release in isolated nerve terminals

In this overview current insights in the regulation of presynaptic transmitter release, mainly acquired in studies using isolated CNS nerve terminals are highlighted. The following aspects are described. (i) The usefulness of pinched-off nerve terminals, so-called synaptosomes, for biochemical and ultrastructural studies of presynaptic stimulus-secretion coupling. (ii) The regulation of neurotransmitter release by multiple Ca2+ channels, with special emphasis on the specificity of different classes of these channels with respect to the release of distinct types of neurotransmitters, that are often co-localized, such as amino acids and neuropeptides. (iii) Possible molecular mechanisms involved in targeting synaptic vesicle (SV) traffic toward the active zone. (iv) The role of presynaptic receptors in regulating transmitter release, with special emphasis on different glutamate subtype receptors. Isolated nerve terminals are of great value as model system in order to obtain a better understanding of the regulation of the release of distinct classes of neurotransmitters in tiny CNS nerve endings.

The novel anticonvulsant BIA 2-093 inhibits transmitter release during opening of voltage-gated sodium channels: a comparison with carbamazepine and oxcarbazepine

(S)-(-)-10-acetoxy-10,11-dihydro-5H-dibenz/b,f/azepine-5-carboxamide (BIA 2-093) is endowed with high anticonvulsant activity and shares with carbamazepine (CBZ) and oxcarbazepine (OXC) the capability to inhibit voltage-gated sodium channels (VGSC). The present study was aimed to compare the effects of BIA 2-093, CBZ and OXC on the release of glutamate, aspartate, gamma-aminobutyric acid (GABA) and dopamine from striatal slices induced by the VGSC opener veratrine. The release of glutamate, aspartate, GABA and aspartate by veratrine from rat striatal slices was a concentration and time dependent process. All the three dibenzazepine carboxamide derivatives, BIA 2-093, CBZ and OXC inhibited in a concentration dependent manner (from 30 to 300 microM) the veratrine-induced release of glutamate, aspartate, GABA and dopamine. CBZ, OXC and BIA 2-093 were endowed with similar potencies in inhibiting veratrine-induced transmitter release. It is concluded that BIA 2-093, CBZ and OXC inhibit veratrine-induced transmitter release, which is in agreement with their capability to block VGSC. This property may be of importance for the anticonvulsant effects of BIA 2-093.

Mechanisms of action of carbamazepine and its derivatives, oxcarbazepine, BIA 2-093, and BIA 2-024

Carbamazepine (CBZ) has been extensively used in the treatment of epilepsy, as well as in the treatment of neuropathic pain and affective disorders. However, the mechanisms of action of this drug are not completely elucidated and are still a matter of debate. Since CBZ is not very effective in some epileptic patients and may cause several adverse effects, several antiepileptic drugs have been developed by structural variation of CBZ, such as oxcarbazepine (OXC), which is used in the treatment of epilepsy since 1990. (S)-(-)-10-acetoxy-10,11-dihydro-5H-dibenz [b,f]azepine-5-carboxamide (BIA 2-093) and 10,11-dihydro-10-hydroxyimino-5H-dibenz[b,f] azepine-5-carboxamide (BIA 2-024), which were recently developed by BIAL, are new putative antiepileptic drugs, with some improved properties. In this review, we will focus on the mechanisms of action of CBZ and its derivatives, OXC, BIA 2-093 and BIA 2-024. The available data indicate that the anticonvulsant efficacy of these AEDs is mainly due to the inhibition of sodium channel activity.

Future prospects for the drug treatment of epilepsy

Great progress has been made in the last 150 years in the pharmacological management of epilepsy, and, despite the increasing number of technological advances available, antiepileptic drugs (AEDs) remain the mainstay of treatment for the vast majority of patients with epilepsy. This review looks at possible avenues of development in the drug treatment of epilepsy. The strengths and weaknesses of those AEDs which are currently licensed are examined, and ways in which their use may be improved are discussed (e.g. rational combinations, use of new formulations). Potentially new targets that may allow the development of effective treatments are highlighted (neuroimmunological manipulation, decreasing inherent drug resistance mechanisms, and modification of adenosine neurotransmission), and a summary of the most promising AEDs currently in development is provided [e.g. carabersat, ganaxolone, harkoseride, MDL 27192, safinamide (NW 1015), pregabalin, retigabine, talampanel, valrocemide, losigamone and BIA 2093].