Pharmacological studies on lamotrigine, a novel potential antiepileptic drug: I. Anticonvulsant profile in mice and rats

Dual Mechanisms of the Diazepine-Benzimidazole Derivative, DAB-19, in Modulating Glutamatergic Neurotransmission

The search for novel compounds with anticonvulsant properties remains a key focus in neuropharmacology. Recently, the diazepine-benzimidazole derivative, DAB-19, has emerged as a promising candidate due to its demonstrated anxiolytic and analgesic effects. In this study, we investigate the mechanisms underlying DAB-19's activity, focusing on its impact on glutamatergic transmission, a key target in the pathophysiology of various central nervous system disorders. Intriguingly, while DAB-19 suppressed evoked glutamatergic transmission in rat brain slices, it simultaneously enhanced spontaneous neurotransmission. Further experiments on glutamatergic neuromuscular synapses in fly larvae revealed two distinct mechanisms: calcium-dependent potentiation of glutamate release and inhibition of spike propagation via blockade of voltage-gated sodium channels. The latter effect was directly confirmed in rat brain neurons. Given its action on sodium channels, we tested DAB-19 in the pentylenetetrazole model, where it delayed seizure onset but did not prevent seizures. These findings position DAB-19 as a multifaceted compound with significant therapeutic potential.

Molecularly Imprinted Drug Carrier for Lamotrigine-Design, Synthesis, and Characterization of Physicochemical Parameters

This study presents the initial attempt at introducing a magnetic molecularly imprinted polymer (MIP) designed specifically for lamotrigine with the purpose of functioning as a drug carrier. First, the composition of the magnetic polymer underwent optimization based on bulk polymer adsorption studies and theoretical analyses. The magnetic MIP was synthesized from itaconic acid and ethylene glycol dimethacrylate exhibiting a drug loading capacity of 3.4 ± 0.9 μg g-1. Structural characterization was performed using powder X-ray diffraction analysis, vibrating sample magnetometry, and Fourier transform infrared spectroscopy. The resulting MIP demonstrated controlled drug released characteristics without a burst effect in the phospahe buffer saline at pH 5 and 8. These findings hold promise for the potential nasal administration of lamotrigine in future applications.

Translational Considerations in the Development of Intranasal Treatments for Epilepsy

Epilepsy is a common and serious neurological disorder, to which a high proportion of patients continue to be considered "drug-resistant", despite the availability of a host of anti-seizure drugs. Investigation into new treatment strategies is therefore of great importance. One such strategy is the use of the nose to deliver drugs directly to the brain with the help of pharmaceutical formulation to overcome the physical challenges presented by this route. The following review explores intranasal delivery of anti-seizure drugs, covering the link between the nose and seizures, pathways from the nose to the brain, current formulations in clinical use, animal seizure models and their proposed application in studying intranasal treatments, and a critical discussion of relevant pre-clinical studies in the literature.

The novel dual-mechanism Kv7 potassium channel/TSPO receptor activator GRT-X is more effective than the Kv7 channel opener retigabine in the 6-Hz refractory seizure mouse model

Epilepsy, one of the most common and most disabling neurological disorders, is characterized by spontaneous recurrent seizures, often associated with structural brain alterations and cognitive and psychiatric comorbidities. In about 30% of patients, the seizures are resistant to current treatments; so more effective treatments are urgently needed. Among the ∼30 clinically approved antiseizure drugs, retigabine (ezogabine) is the only drug that acts as a positive allosteric modulator (or opener) of voltage-gated Kv7 potassium channels, which is particularly interesting for some genetic forms of epilepsy. Here we describe a novel dual-mode-of-action compound, GRT-X (N-[(3-fluorophenyl)-methyl]-1-(2-methoxyethyl)-4-methyl-2-oxo-(7-trifluoromethyl)-1H-quinoline-3-carboxylic acid amide) that activates both Kv7 potassium channels and the mitochondrial translocator protein 18 kDa (TSPO), leading to increased synthesis of brain neurosteroids. TSPO activators are known to exert anti-inflammatory, neuroprotective, anxiolytic, and antidepressive effects, which, together with an antiseizure effect (mediated by Kv7 channels), would be highly relevant for the treatment of epilepsy. This prompted us to compare the antiseizure efficacy of retigabine and GRT-X in six mouse and rat models of epileptic seizures, including the 6-Hz model of difficult-to-treat focal seizures. Furthermore, the tolerability of the two compounds was compared in mice and rats. Potency comparisons were based on both doses and peak plasma concentrations. Overall, GRT-X was more effective than retigabine in three of the six seizure models used here, the most important difference being the high efficacy in the 6-Hz (32 mA) seizure model in mice. Based on drug plasma levels, GRT-X was at least 30 times more potent than retigabine in the latter model. These data indicate that GRT-X is a highly interesting novel anti-seizure drug with a unique (first-in-class) dual-mode mechanism of action.

Lamotrigine-Associated Movement Disorder: A Literature Review

BACKGROUND

Lamotrigine (LMT) is a phenyltriazine derivative that was originally described as an antiepileptic drug.

OBJECTIVE

This literature review aims to evaluate the clinical epidemiological profile, pathological mechanisms, and management of lamotrigine-associated movement disorders.

METHODS

Relevant reports in six databases were identified and assessed by two reviewers without language restriction. Reports that the individuals only developed tremor or ataxia after LMT use were not included.

RESULTS

In total 48 reports of 108 cases from 19 countries were assessed. The movement disorders associated with LMT found were 29 tics, 21 dyskinesias, 14 myoclonus, 13 parkinsonism, 10 dystonia, and 1 stuttering. The not clearly defined cases included 10 akathisia, 4 myoclonus, 4 cerebellar syndromes, 1 hypertonia, 1 dyskinesia, and an unknown number of dystonia cases. The mean reported age was 33.34 years (range: 1.574 years). The male was the predominant sex and the most common LMT indication was epilepsy. The mean LMT-dose at the movement disorder onset was 228 mg. The time from LMT start to the onset of movement disorder was within 6 months in 81%. The time from LMT withdrawal to complete recovery was within 1 month in 83%. The most common management was LMT withdrawal.

CONCLUSIONS

In the literature, the majority of the cases did not give a clear picture of the individual, and the times of movement disorder onset and recovery are not described. We believe that before withdrawal LMT, a dose adjustment based on the benefits and adverse events with careful evaluation case-by-case can be done.

Cannabigerolic acid, a major biosynthetic precursor molecule in cannabis, exhibits divergent effects on seizures in mouse models of epilepsy

Background and Purpose

Cannabis has been used to treat epilepsy for millennia, with such use validated by regulatory approval of cannabidiol (CBD) for Dravet syndrome. Unregulated artisanal cannabis‐based products used to treat children with intractable epilepsies often contain relatively low doses of CBD but are enriched in other phytocannabinoids. This raises the possibility that other cannabis constituents might have anticonvulsant properties.

Experimental Approach

We used the Scn1a^+/− mouse model of Dravet syndrome to investigate the cannabis plant for phytocannabinoids with anticonvulsant effects against hyperthermia‐induced seizures. The most promising, cannabigerolic acid (CBGA), was further examined against spontaneous seizures and survival in Scn1a^+/− mice and in electroshock seizure models. Pharmacological effects of CBGA were surveyed across multiple drug targets.

Key Results

The initial screen identified three phytocannabinoids with novel anticonvulsant properties: CBGA, cannabidivarinic acid (CBDVA) and cannabigerovarinic acid (CBGVA). CBGA was most potent and potentiated the anticonvulsant effects of clobazam against hyperthermia‐induced and spontaneous seizures, and was anticonvulsant in the MES threshold test. However, CBGA was proconvulsant in the 6‐Hz threshold test and a high dose increased spontaneous seizure frequency in Scn1a^+/− mice. CBGA was found to interact with numerous epilepsy‐relevant targets including GPR55, TRPV1 channels and GABA_A receptors.

Conclusion and Implications

These results suggest that CBGA, CBDVA and CBGVA may contribute to the effects of cannabis‐based products in childhood epilepsy. Although these phytocannabinoids have anticonvulsant potential and could be lead compounds for drug development programmes, several liabilities would need to be overcome before CBD is superseded by another in this class.

A new 1 : 1 cocrystal of lamotrigine and 1,2,3,6-hydrophthalimide: discovery, characterization, and construction of ternary phase diagrams

A 1 : 1 cocrystal of lamotrigine (LAM) with 1,2,3,6-tetrahydrophthalimide (HPHT) was first successfully synthesized. The ternary phase diagram of the cocrystal was constructed, and its stability and dissolution were determined.

The Effectiveness of Lamotrigine and Its Blood Levels for Pediatric Epilepsy

This study was conducted to evaluate the effectiveness of lamotrigine (LTG) over 2 years and the usefulness of measuring its blood levels during the follow-up of patients with epilepsy. We measured peak blood LTG levels of 32 patients with epilepsy (9.16 ± 3.34 years old; mean ± SD). The blood levels were measured at 6 months, 1 year, and 2 years after reaching the LTG maintenance dosage. The effectiveness of LTG was evaluated to determine the seizure reduction rate. The patients were classified as effective cases (mean of own seizure reduction rates >50%) and ineffective cases (≤50%). The results were that the dosage and blood level showed positive correlations in the case of combination use with sodium valproate (VPA) (r = 0.690), carbamazepine and/or phenobarbital (r = 0.940), and others (r = 0.548). In several groups, the blood levels and efficacies did not show any positive correlations. In the cases of combination use with VPA, the blood levels of effective cases and ineffective cases were significantly different (P = 0.001). The optimal range was 8-11.5 μg/mL based on the average and SD values in the effective cases. No patients had any side effects. In conclusion, no precise definition of the therapeutic range was possible because of the incomplete correlation between the blood level and seizure frequency. We recommend the optimal range of LTG as a therapeutic target without any side effects, and it was established that the range in the combination with VPA was 8-11.5 μg/mL.

Multidrug Cocrystal of Anticonvulsants: Influence of Strong Intermolecular Interactions on Physiochemical Properties

A drug-drug cocrystal of two anticonvulsants, lamotrigine and phenobarbital, is presented. In the crystal structure, molecules form heterodimers via N-H···O and N-H···N hydrogen bonding. The intrinsic dissolution rate (IDR) and solubility of the cocrystal were measured in phosphate buffer (pH 7.2) and simulated gastric fluid (without pepsin), and compared to pure APIs. Dissolution experiments found suppressed IDR of the cocrystal with rates in the order pure PB > pure LTG > cocrystal. The solubility measurements were consistent with the dissolution behavior. The presence of strong heterodimers in the cocrystal compared to weaker homodimers in the parent drugs is implicated for the reduced solubility and dissolution rate.

Pharmacological and neuroethological study of the acute and chronic effects of lamotrigine in the genetic audiogenic seizure hamster (GASH:Sal)

The present study aimed to investigate the behavioral and anticonvulsant effects of lamotrigine (LTG) on the genetic audiogenic seizure hamster (GASH:Sal), an animal model of audiogenic seizure that is in the validation process. To evaluate the efficiency of acute and chronic treatments with LTG, GASH:Sals were treated with LTG either acutely via intraperitoneal injection (5-20mg/kg) or chronically via oral administration (20-25mg/kg/day). Their behavior was assessed via neuroethological analysis, and the anticonvulsant effect of LTG was evaluated based on the appearance and the severity of seizures. The results showed that acute administration of LTG exerts an anticonvulsant effect at the lowest dose tested (5mg/kg) and that chronic oral LTG treatment exerts an anticonvulsant effect at a dose of 20-25mg/kg/day. Furthermore, LTG treatment induced a low rate of secondary adverse effects. This article is part of a Special Issue entitled "Genetic and Reflex Epilepsies, Audiogenic Seizures and Strains: From Experimental Models to the Clinic".

Efficacy of anticonvulsant substances in the 6Hz seizure test: Comparison of two rodent species

Usually performed in the mouse, the 6Hz seizure test is used for screening potential new anticonvulsant substances against complex partial seizures. Nevertheless, advanced models of temporal lobe epilepsy (TLE) are more often performed in rats, so that possible species-related differences may complicate the development of anticonvulsant substances. The aim of the present study was to evaluate the feasibility of adapting the 6Hz test in the rat. We first compared the effects of increasing current intensities for inducing seizures in the mouse and in the rat. This step was followed by the evaluation of the activity of anticonvulsant substances. Animals received an electrical stimulation with a constant current via corneal electrodes. The seizure was characterized by the presence of forelimb clonus immediately after stimulation. Spontaneous locomotion was evaluated following the 6Hz test. In the rat, the forelimb seizure score was intensity-dependently increased and seizures were observed in all animals tested at 44mA. In the mouse, the seizures were of lower magnitude and they were not observed in all mice stimulated at 44mA. In both species, levetiracetam (LEV) clearly decreased the forelimb seizure score over the dose-range 100-300mg/kg without affecting locomotion. Valproate (VPA) displayed anticonvulsant activity at 200mg/kg and fully protected both species at 300mg/kg, a dose producing sedative effects in the mouse. Phenytoin (PHT) showed slight to moderate anticonvulsant activity at 100mg/kg in the mouse and at 60 and 100mg/kg in the rat without modifying locomotor activity. Lamotrigine (LTG) partially antagonized forelimb seizure at 60mg/kg in the mouse and at 30-60mg/kg in the rat, but it induced clear motor impairments at high dose in both species. Our data suggest that in the 6Hz test, the magnitude and the nature of seizures differed between the mouse and the rat for a given current intensity. Nevertheless, the pharmacological profile of anticonvulsant substances was similar in both species for the 4 substances tested. Dose-dependent efficacy of LEV and VPA was observed and LTG and PHT also showed anticonvulsant activity, even though the magnitude of the effects remained moderate for these two last substances. The 6Hz test in the rat therefore appears as a useful model which may be performed prior to follow-up models of partial seizures performed in the same species.

Evaluation of the pentylenetetrazole seizure threshold test in epileptic mice as surrogate model for drug testing against pharmacoresistant seizures

Resistance to antiepileptic drugs (AEDs) is a major problem in epilepsy therapy, so that development of more effective AEDs is an unmet clinical need. Several rat and mouse models of epilepsy with spontaneous difficult-to-treat seizures exist, but because testing of antiseizure drug efficacy is extremely laborious in such models, they are only rarely used in the development of novel AEDs. Recently, the use of acute seizure tests in epileptic rats or mice has been proposed as a novel strategy for evaluating novel AEDs for increased antiseizure efficacy. In the present study, we compared the effects of five AEDs (valproate, phenobarbital, diazepam, lamotrigine, levetiracetam) on the pentylenetetrazole (PTZ) seizure threshold in mice that were made epileptic by pilocarpine. Experiments were started 6 weeks after a pilocarpine-induced status epilepticus. At this time, control seizure threshold was significantly lower in epileptic than in nonepileptic animals. Unexpectedly, only one AED (valproate) was less effective to increase seizure threshold in epileptic vs. nonepileptic mice, and this difference was restricted to doses of 200 and 300 mg/kg, whereas the difference disappeared at 400mg/kg. All other AEDs exerted similar seizure threshold increases in epileptic and nonepileptic mice. Thus, induction of acute seizures with PTZ in mice pretreated with pilocarpine does not provide an effective and valuable surrogate method to screen drugs for antiseizure efficacy in a model of difficult-to-treat chronic epilepsy as previously suggested from experiments with this approach in rats.

Certain secondary antiepileptic drugs can rescue hippocampal injury following a critical growth period despite poor anticonvulsant activity and cognitive deficits

Clinical and experimental studies have shown that many common secondary antiepileptic drugs (AEDs) are ineffective at blocking seizures in adulthood; however, some afford neuroprotection. In early development, certain AEDs cause apoptosis; however, it is unknown whether these drugs are neurotoxic to the juvenile brain following a developmentally regulated proapoptotic period and whether they alter the seizure threshold, seizure-induced neuronal vulnerability, and/or cognitive function. Lamotrigine (LTG), carbamazepine (CBZ), phenytoin (PHT), valproate (VPA), and topiramate (TPM) were systemically administered to rat pups for 7days beginning on postnatal (P) day 14 (P14), then half the animals were injected with kainate (KA) to trigger seizures, an age when the CA1 subregion becomes preferentially sensitive to status epilepticus. Histological outcome, seizure severity, and learning and memory were determined with an electroencephalograph (EEG), silver impregnation, and a water-maze swim task. None of the AEDs tested significantly attenuated behavioral or electrographic seizures. Phenytoin increased mortality, identifying a detrimental side effect of this drug. The other drugs (LTG, VPA, TPM, and CBZ) afforded different amounts of protection to the CA1 subregion but not to the CA3 subregion or extrahippocampal structures. With the exception of VPA, AED-treated animals lagged behind during swim task acquisition. All groups improved in the water-maze swim task over time, particularly on the last trials; however, the average escape latency was still impaired for TPM-treated animals and all AED+KA-treated groups. Thus, while certain AEDs demonstrated some neuroprotective effects, poor antiepileptic activity, memory impairment, and other deleterious side effects were observed with these drugs suggesting that the search for potentially more effective and tolerated agents is essential for improving clinical outcome in children and adolescents with epilepsy.

Liquid chromatography tandem mass spectrometry method for the estimation of lamotrigine in human plasma: Application to a pharmacokinetic study

A reliable, selective and sensitive liquid chromatography tandem mass spectrometry method was developed and validated for the quantification of lamotrigine in human plasma using lamotrigine-¹³C3, d3 as an internal standard. Analyte and internal standard were extracted from human plasma by solid-phase extraction and detected in positive ion mode by tandem mass spectrometry with electrospray ionization (ESI) interface. Chromatographic separation was performed on a Chromolith^® SpeedROD; RP-18e column (50−4.6 mm i.d.) using acetonitrile: 5±0.1 mM ammonium formate solution (90:10, v/v) as the mobile phase at a flow rate of 0.500 mL/min. The calibration curves were linear over the range of 5.02–1226.47 ng/mL with the lower limit of quantitation validated at 5.02 ng/mL. The analytes were found stable in human plasma through three freeze (−20 °C)-thaw (ice-cold water bath) cycles and under storage on bench-top in ice-cold water bath for at least 6.8 h, and also in the mobile phase at 10 °C for at least 57 h. The method has shown good reproducibility, as the intra- and inter-day precisions were within 3.0%, while the accuracies were within ±6.0% of nominal values. The validated LC–MS/MS method was applied for the evaluation of pharmacokinetic and bioequivalence parameters of lamotrigine after an oral administration of 50 mg lamotrigine tablet to thirty-two healthy adult male volunteers.

The psychopharmacology of aggressive behavior: a translational approach: part 2: clinical studies using atypical antipsychotics, anticonvulsants, and lithium

Patients experiencing mental disorders are at an elevated risk for developing aggressive behavior. In the past 10 years, the psychopharmacological treatment of aggression has changed dramatically owing to the introduction of atypical antipsychotics on the market and the increased use of anticonvulsants and lithium in the treatment of aggressive patients.This review (second of 2 parts) uses a translational medicine approach to examine the neurobiology of aggression, discussing the major neurotransmitter systems implicated in its pathogenesis (serotonin, glutamate, norepinephrine, dopamine, and γ-aminobutyric acid) and the neuropharmacological rationale for using atypical antipsychotics, anticonvulsants, and lithium in the therapeutics of aggressive behavior. A critical review of all clinical trials using atypical antipsychotics (aripiprazole, clozapine, loxapine, olanzapine, quetiapine, risperidone, ziprasidone, and amisulpride), anticonvulsants (topiramate, valproate, lamotrigine, and gabapentin), and lithium are presented. Given the complex, multifaceted nature of aggression, a multifunctional combined therapy, targeting different receptors, seems to be the best strategy for treating aggressive behavior. This therapeutic strategy is supported by translational studies and a few human studies, even if additional randomized, double-blind, clinical trials are needed to confirm the clinical efficacy of this framework.

Influence of nebivolol on anticonvulsant effect of lamotrigine

Objective:

The present study describes the effect of nebivolol (NBV) either alone or in combination with lamotrigine (LTG) using increasing current electroshock seizures (ICES) model in mice.

Materials and Methods:

Male albino mice of Swiss strain each weighing 18-30 g were used. Lamotrigine (Lamitor tablets, Torrent; 1.5 and 3.0 mg/kg) and NBV (Nebicard tablets, Torrent; 0.25 and 0.5 mg/kg) were suspended in 0.25% of carboxy methyl cellulose (CMC) in 0.9% saline and administered orally in volumes of 10 mg/kg. Control animals received an equivalent volume of 0.25% CMC in 0.9% saline suspension. The anticonvulsant effects of the drugs were measured using ICES model whereas cognitive behavior was measured by the spontaneous alternation behavior and grip-strength test. The biochemical estimation was done by measuring the lipid peroxidation and reduced glutathione (GSH).

Results:

Both NBV and LTG produced significantly enhanced seizure threshold (ST), decreased grip strength, inhibited lipid peroxidation, and increased brain GSH levels in acute and chronic dosages likened to control group, whereas there was no significant effect on alternation scores. The combination of NBV with LTG significantly potentiated the ST when compared to LTG.

Conclusion:

Nebivolol showed antiepileptic effects in addition to its reported antihypertensive effect, which could be attributed to action of the two drugs through different mechanisms or due to drug interaction that may be pharmacodynamic or pharmacokinetic needing elucidation.

Difficulties in Treatment and Management of Epilepsy and Challenges in New Drug Development

Epilepsy is a serious neurological disorder that affects around 50 million people worldwide. Almost 30% of epileptic patients suffer from pharmacoresistance, which is associated with social isolation, dependent behaviour, low marriage rates, unemployment, psychological issues and reduced quality of life. Currently available antiepileptic drugs have a limited efficacy, and their negative properties limit their use and cause difficulties in patient management. Antiepileptic drugs can provide only symptomatic relief as these drugs suppress seizures but do not have ability to cure epileptogenesis. The long term use of antiepileptic drugs is limited due to their adverse effects, withdrawal symptoms, deleterious interactions with other drugs and economic burden, especially in developing countries. Furthermore, some of the available antiepileptic drugs may even potentiate certain type of seizures. Several in vivo and in vitro animal models have been proposed and many new antiepileptic drugs have been marketed recently, but large numbers of patients are still pharmacoresistant. This review will highlight the difficulties in treatment and management of epilepsy and the limitations of available antiepileptic drugs and animal seizure models.

The investigational anticonvulsant lacosamide selectively enhances slow inactivation of voltage-gated sodium channels

We hypothesized that lacosamide modulates voltage-gated sodium channels (VGSCs) at clinical concentrations (32-100 muM). Lacosamide reduced spiking evoked in cultured rat cortical neurons by 30-s depolarizing ramps but not by 1-s ramps. Carbamazepine and phenytoin reduced spike-firing induced by both ramps. Lacosamide inhibited sustained repetitive firing during a 10-s burst but not within the first second. Tetrodotoxin-sensitive VGSC currents in N1E-115 cells were reduced by 100 muM lacosamide, carbamazepine, lamotrigine, and phenytoin from V(h) of -60 mV. Hyperpolarization (500 ms) to -100 mV removed the block by carbamazepine, lamotrigine, and phenytoin but not by lacosamide. The voltage-dependence of activation was not changed by lacosamide. The inactive S-stereoisomer did not inhibit VGSCs. Steady-state fast inactivation curves were shifted in the hyperpolarizing direction by carbamazepine, lamotrigine, and phenytoin but not at all by lacosamide. Lacosamide did not retard recovery from fast inactivation in contrast to carbamazepine. Carbamazepine, lamotrigine, and phenytoin but not lacosamide all produced frequency-dependent facilitation of block of a 3-s, 10-Hz pulse train. Lacosamide shifted the slow inactivation voltage curve in the hyperpolarizing direction and significantly promoted the entry of channels into the slow inactivated state (carbamazepine weakly impaired entry into the slow inactivated state) without altering the rate of recovery. Lacosamide is the only analgesic/anticonvulsant drug that reduces VGSC availability by selective enhancement of slow inactivation but without apparent interaction with fast inactivation gating. The implications of this unique profile are being explored in phase III clinical trials for epilepsy and neuropathic pain.

The pharmacokinetics of antiepileptic drugs in rats: consequences for maintaining effective drug levels during prolonged drug administration in rat models of epilepsy

Rodent models of chronic epilepsy with spontaneous recurrent seizures likely represent the closest parallel to the human condition. Such models may be best suited for therapy discovery for pharmacoresistant epilepsy and for antiepileptogenic or disease-modifying therapeutics. However, the use of such rodent models for therapy discovery creates problems with regard to maintaining effective drug levels throughout a prolonged testing period. This is particularly due to the fact that rodents such as rats and mice eliminate most drugs much more rapidly than humans. Thus, knowledge about elimination rate of a test drug in a laboratory species is essential for development of a treatment paradigm that allows maintaining adequate drug levels in the system over the period of treatment. Currently, the most popular models of epilepsy with spontaneous seizures are poststatus epilepticus models of temporal lobe epilepsy in rats. Such models are both used for studies on antiepileptogenesis and drug resistance. For validation of these models, current antiepileptic drugs (AEDs) have to be used. In this article, the elimination rates of these AEDs and their effective plasma levels in rats are reviewed as a guide for developing treatment protocols for chronic drug testing. The advantages and disadvantages of several technologies for drug delivery are discussed, and some examples for calculation of adequate treatment protocols are given. As shown in this review, because of the rapid elimination of most AEDs in rats, it is no trivial task to maintain effective steady-state AED levels in the plasma throughout the day over multiple days to ensure that there will be adequate levels in the system for the purpose of the experiment. However, the use of an adequate dosing regimen that is based on elimination rate is an absolute prerequisite when using rat models for discovery of new antiepileptogenic therapies or therapies for pharmacoresistant epilepsy, because otherwise such models may lead to erroneous conclusions about drug efficacy.

Activity profile of pregabalin in rodent models of epilepsy and ataxia

Pregabalin (Lyrica) is a novel amino acid compound that binds with high affinity to the alpha2-delta (alpha2-delta) auxiliary protein of voltage-gated calcium channels. In vivo, it potently prevents seizures, pain-related behaviors and has anxiolytic-like activity in rodent models. The present studies were performed to determine the profile of pregabalin anticonvulsant activity in a variety of mouse and rat models. In the high-intensity electroshock test, pregabalin potently inhibited tonic extensor seizures in rats (ED50 = 1.8 mg/kg, PO), and low-intensity electroshock seizures in mice. It prevented tonic extensor seizures in the DBA/2 audiogenic mouse model (ED50 = 2.7 mg/kg, PO). Its time course of action against electroshock induced seizures in rats roughly followed the pharmacokinetics of radiolabeled drug in the brain compartment. At higher dosages (ED50 1= 31 mg/kg, PO), pregabalin prevented clonic seizures from pentylenetetrazole in mice. In a kindled rat model of partial seizures, pregabalin prevented stages 4-5 behavioral seizures (lowest effective dose = 10 mg/kg, IP), and also reduced the duration of electrographic seizures. Pregabalin was not active to prevent spontaneous absence-like seizures in the Genetic Absence Epilepsy in Rats from Strasbourg (GAERS) inbred Wistar rat strain. Pregabalin caused ataxia and decreased spontaneous locomotor activity at dosages 10-30-fold higher than those active to prevent seizures. These findings suggest that pregabalin has an anticonvulsant mechanism different from the prototype antiepileptic drugs and similar to that of gabapentin except with increased potency and bioavailability. In summary, our results show that pregabalin has several properties that favor treatment of partial seizures in humans.

Lamotrigine pharmacokinetic/pharmacodynamic modelling in rats

The aim of this study was to perform a pharmacokinetic/pharmacodynamic (PK/PD) modelling of lamotrigine following its acute administration to rats. Adult male Wistar rats were given 10 mg/kg of lamotrigine intraperitoneally. Plasma and brain samples were obtained at predetermined times over 120 h post-dose and analysed by liquid chromatography. The anticonvulsant profile against maximal electroshock seizure stimulation was determined over 48 h after dosing. As a linear relationship between lamotrigine plasma and brain profiles was observed, only the plasma data set was used to establish the PK/PD relationship. To fit the effect-time course of lamotrigine, the PK/PD simultaneous fitting link model was used: the pharmacokinetic parameters and dosing information were used in the one-compartment first-order model to predict concentrations, which were then used to model the pharmacodynamic data with the sigmoid Emax model, in order to estimate all the parameters simultaneously. The following parameters were obtained: Vd = 2.00 L/kg, k(abs) = 8.50 h(-1), k(el) = 0.025 h(-1), k(e0) = 3.75 h(-1), Emax = 100.0% (fixed), EC50 = 3.44 mg/L and gamma = 8.64. From these results, it can be stated that lamotrigine is extensively distributed through the body, its plasma elimination half-life is around 28 h and a lamotrigine plasma concentration of 3.44 mg/L is enough to protect 50% of the animals. When compared with humans, the plasma concentrations achieved with this dose were within the therapeutic concentration range that had been proposed for epileptic patients. With the present PK/PD modelling it was possible to fit simultaneously the time-courses of the plasma levels and the anticonvulsant effect of lamotrigine, providing information not only about the pharmacokinetics of lamotrigine in the rat but also about its anticonvulsant response over time. As this approach can be easily applied to other drugs, it becomes a useful tool for an explanatory comparison between lamotrigine and other antiepileptic drugs.

Cortical excitability during prolonged antiepileptic drug treatment and drug withdrawal

OBJECTIVE

Previous reports characterized the effects of administration of single oral doses of antiepileptic drugs (AED) on cortical excitability. However, AED effects on cortical excitability, and their relationship to plasma blood levels, during chronic drug administration at therapeutic doses are not known. The objective of the study was to determine whether plasma blood levels during chronic administration at therapeutic doses would accurately predict changes in corticomotor excitability.

METHODS

We used transcranial magnetic stimulation (TMS) to measure cortical excitability during 5 weeks administration of carbamazepine (CBZ) and lamotrigine (LTG), and subsequent AED withdrawal in 20 healthy volunteers. Data were analyzed using ANOVA(RM) and regression analysis.

RESULTS

Resting motor thresholds (r-MT) increased with increasing total and free CBZ and LTG levels during drug administration, but not drug withdrawal. After acute AED withdrawal, r-MT elevation persisted in most individuals with CBZ despite undetectable plasma levels, compared to a rapid normalization with LTG. In contrast, acute drug withdrawal resulted in a transient decrease in r-MT in 3/10 individuals with CBZ and 2/10 with LTG.

CONCLUSIONS

Plasma levels provide information on motor cortical function during active treatment phases but not during AED withdrawal.

SIGNIFICANCE

The transient decrease in r-MT associated with acute AED withdrawal could represent a physiological substrate contributing to AED withdrawal seizures.

Lamotrigine has an anxiolytic-like profile in the rat conditioned emotional response test of anxiety: a potential role for sodium channels?

RATIONALE

Many anticonvulsants are used in disorders other than epilepsy. For example, lamotrigine is reported to be effective in post-traumatic stress disorder and mania.

OBJECTIVE

We assessed the effects of the anticonvulsants lamotrigine, valproate and carbamazepine in an animal model of anxiety. We assessed a wide range of pharmacological tools to delineate the mechanism of lamotrigine's anxiolytic effect.

METHODS

We assessed these compounds in the rat conditioned emotional response (CER) test of anxiety.

RESULTS

Lamotrigine (30-80 mg/kg) dose-dependently and reproducibly engendered an anxiolytic response in this test, with similar efficacy to benzodiazepines. Carbamazepine (20-40 mg/kg) and riluzole (10 mg/kg), which block Na+ channels by a similar mechanism as lamotrigine, were also anxiolytic. By contrast, valproate (100-600 mg/kg) was inactive and appears to differ in its interaction with Na+ channels. The SSRI paroxetine, the GABA(A) receptor positive modulator propofol, the NMDA antagonists memantine and (+)MK-801, and the Ca2+ channel antagonist nifedipine were all inactive in the CER test, suggesting these mechanisms may not mediate the anxiolytic effect of lamotrigine. More directly, we showed that the anxiolytic effect of lamotrigine could be blocked by co-administering rats with the Na+ channel activator veratrine (0.1 mg/kg). By contrast, neither the Ca2+ channel agonist BAYK8644 (0.5 mg/kg) nor the 5-HT1A or 5-HT(1/2) antagonists WAY100635 (0.3 mg/kg) and metergoline (3 mg/kg), respectively, were able to block the effect.

CONCLUSION

Lamotrigine's anxiolytic effect in the CER test may be mediated via block of Na+ channels, and this may represent a target for the development of novel anxiolytics.

Interaction between lamotrigine and felbamate in the maximal electroshock-induced seizures in mice: an isobolographic analysis

Isobolographic profile of interactions between lamotrigine (LTG) and felbamate (FBM), two second-generation antiepileptic drugs, against maximal electroshock (MES)-induced seizures, and neurotoxic adverse effects in the chimney test in mice were determined. LTG combined with FBM at the fixed ratios of 1:3, 1:1, and 3:1 exerted merely additive interactions against MES-induced seizures. In the chimney test, isobolography revealed that LTG coadministered with FBM at the fixed ratio of 1:1 displayed subadditivity (antagonism), whereas the remaining combinations tested (1:3 and 3:1) exerted additivity in terms of their neurotoxic side effects. LTG (at the dose of 2.3 mg/kg) coadministered with FBM (25.7 mg/kg) at the fixed ratio of 1:1 from the MES test did not impair long-term memory of mice challenged with the passive avoidance task. Furthermore, FBM (25.7 mg/kg) altered neither the free plasma nor brain concentration of LTG, hence pharmacokinetic events, which might affect the observed interactions in the MES test, are unlikely. Considering benefit indices for the respective fixed ratio combinations, it may be concluded that the combination of LTG with FBM at the fixed ratio of 1:1 is advantageous from a preclinical point of view, offering the highest benefit index reaching the value of 1.46. Likewise, the two-drug combination of 1:3 was also beneficial and is worth recommendation with benefit index amounting to 1.36. Only the combination of 3:1 was neutral with a benefit index of 1.08. Protection offered by LTG in combination with FBM against maximal electroconvulsions and its favorable neurotoxic side effect profile might provide the patients with intractable seizures with an efficacious treatment, as the rational polytherapy however, it requires to be clinically confirmed and verified.

Effects of the combination of valproate and ethosuximide on spike wave discharges in WAG/Rij rats

OBJECTIVE

We studied the interaction between valproate (VPA) and ethosuximide (ESM) in diminishing the incidence of absence-like spike-wave discharges (SWDs) in the EEG of WAG/Rij rats.

METHODS

VPA, ESM, their combination and saline were evaluated in 16 rats. The doses of VPA ranged from 0 to 280 mg/kg and the doses of ESM ranged from 0 to 40 mg/kg. For the drug combination, a fixed weight ratio of 7/1 VPA/ESM was used. The incidence of SWDs in the EEG was determined for the period of 15-75 min after injection and compared to the incidence of SWDs prior to injection. The sigmoid-E(max) equation was fitted to the data. Isobolic analysis, on 50% effect, was used to assess the character of the drug interaction.

RESULTS

The parameters for diminishing the incidence of the SWDs were: VPA: ED(50): 121mg/kg; ESM: ED(50): 21.5mg/kg; VPA/ESM: ED(50): 112/16 mg/kg. Isobolic analysis showed that a higher drug load was needed of the combination than of the individual drugs to achieve a 50% reduction of SWDs: factor 1.67; P = 0.012.

CONCLUSION

The interaction between valproate and ethosuximide was shown to be infra-additive in diminishing the incidence of SWDs in WAG/Rij rats.

Lamotrigine does not impair motor performance and spontaneous behavior in developing rats

No data exist on possible effects of lamotrigine on development. Therefore we performed an ontogenetic study with repeated administration of lamotrigine (10 and/or 20 mg/kg ip for 6 consecutive days) starting in rats 12 and 25 days old (Postnatal Days (PD) 12 and 25). Body weights of these animals were checked, their motor skills were repeatedly tested, and their behavior in an open field was studied at three intervals after the end of treatment. Body weight of PD12 animals increased more slowly than that of control siblings; this difference disappeared till adulthood. There were only transient changes on the bar holding test in the PD12 group and on the rotorod test in the PD25 group. The open-field test demonstrated greater exploratory activity (rearing) in the PD25 group only at the age of 48 days but not 1 month later. Lamotrigine administered repeatedly at early developmental stages did not change motor abilities and behavior in an open field.

Treatment Strategies for Myoclonic Seizures and Epilepsy Syndromes with Myoclonic Seizures

Despite the availability of numerous treatment options, the diagnosis and treatment of myoclonic seizures continue to be challenging. Based on clinical experience, valproate and benzodiazepines have historically been used to treat myoclonic seizures. However, many more treatment options exist today, and the clinician must match the appropriate treatment with the patient's epilepsy syndrome and its underlying etiology. Comorbidities and other medications must also be considered when making decisions regarding treatment. Rarely, some antiepileptic drugs may exacerbate myoclonic seizures. Most epileptic myoclonus can be treated pharmacologically, but some cases respond better to surgery, the ketogenic diet, or vagus nerve stimulation. Because myoclonic seizures can be difficult to treat, clinicians should be flexible in their approach and tailor therapy to each patient.

Interactions of lamotrigine with topiramate and first-generation antiepileptic drugs in the maximal electroshock test in mice: an isobolographic analysis

PURPOSE

The study investigated the types of interactions between lamotrigine (LTG) and first-generation antiepileptic drugs (AEDs) or topiramate (TPM) with isobolographic analysis.

METHODS

Anticonvulsant and adverse-effect profiles of combinations of LTG with other AEDs, at fixed ratios of 1:3, 1:1, and 3:1, were evaluated in the maximal electroshock (MES)-induced seizures and the chimney test (motor performance) in mice, which allowed the determination of benefit indices (BIs) for individual combinations.

RESULTS

Combinations of LTG with TPM or valproate (VPA), at fixed ratios of 1:1, were significantly supraadditive (synergistic) in the MES test and, simultaneously, subadditive (antagonistic) in the chimney test, showing the best profile for AED combinations. In contrast, combinations between LTG and carbamazepine (CBZ), in terms of antiseizure protection against MES, were subadditive (antagonistic) and additive in the chimney test, resulting in unfavorable AED combinations. Moreover, the combination of LTG with phenobarbital (PB), at a fixed ratio of 1:1, despite synergy in the MES test, also was synergistic in the chimney test, resulting in a modest BI for AED combination. LTG combined with phenytoin was additive in both the MES and chimney tests in mice. The remaining combinations, at fixed ratios not mentioned earlier, also showed an average BI for AED combinations. Furthermore, LTG combined with all studied AEDs did not affect long-term memory in mice. None of the AEDs influenced the free plasma level of LTG, whereas LTG slightly reduced the free plasma concentration of PB.

CONCLUSIONS

Interactions between LTG and TPM or LTG and VPA at a fixed ratio of 1:1 might be profitable from a preclinical point of view, displaying the most optimal BI.

The influence of anticonvulsant and antioxidant drugs on nitric oxide level and lipid peroxidation in the rat brain during penthylenetetrazole-induced epileptiform model seizures

Nitric oxide (NO) generation in the brain cortex of Wistar rats was measured by direct method of electron paramagnetic resonance (EPR) spectroscopy. Dramatic (fivefold) elevation of NO production was found during penthylenetetrazole (PTZ)-induced epileptiform seizures. The level of secondary products of lipid peroxidation (LPO; thiobarbituric acid reactive substances, TBARS) was also significantly increased in the cerebral cortex of rats with PTZ-evoked seizures. The effects of anticonvulsant drugs phenobarbital, lamotrigine, phenazepam, as well as antioxidant substances alpha-tocopherol and novel original Russian synthetic drug mexidol (2-ethyl-6-methyl-3-oxypiridine succinate), were investigated. All the substances studied significantly decreased seizure manifestations and partially prevented both enhancement of NO generation and increase in TBARS formation. Mexidol and phenobarbital were found to be the most effective in the preventing of PTZ-induced seizures among all the substances studied. The data obtained support our speculation that neuroprotective action of mexidol may correlate with its ability to inhibit not only excessive reactive oxygen species (ROS) formation but also NO generation. While the molecular mechanism underlying action of mexidol and phenobarbital still remains unclear, it is likely that the effect of these drugs on NO production is contributing to their neuroprotective action. It might be concluded that both the suppression of seizure-induced NO generation and LPO enhancement may be involved in the mechanism of action of antiepileptic drugs.

Synergistic interaction between felbamate and lamotrigine against seizures induced by 4-aminopyridine and pentylenetetrazole in mice

We compared the effects of adding a nonprotective dose of felbamate to increasing single doses of lamotrigine with those of monotherapy and vice versa in CD1 mice. Anticonvulsant effects were evaluated against seizures induced by both 14 mg/kg of 4-aminopyridine and 110 mg/kg of pentylenetetrazole, and neurotoxic effects were evaluated by the rotarod test. Changes in anticonvulsants, gamma-aminobutyric acid (GABA) and glutamate concentrations in the whole brain were also assessed. Lamotrigine increased the potency ratio of felbamate against 4-aminopyridine (1.80, 95% confidence interval (CI) 1.23-2.65, P<0.05) but not against pentylenetetrazole nor on rotarod, the protective index being increased from 12.0 to 17.1 for 4-aminopyridine, with a reduction in brain felbamate, and with an increase in brain GABA. Felbamate increased the potency ratio of lamotrigine against 4-aminopyridine (4.35, 95% CI 2.05-9.25, P<0.05) but not on rotarod, the protective index being increased from 4.4 to 15.7; there were no changes in brain lamotrigine, and changes in brain GABA and/or glutamate were unrelated to the pharmacodynamic effects. In conclusion, a nonprotective dose of lamotrigine increased the therapeutic index of felbamate and vice versa, and these effects appeared to be pharmacodynamic.

Effects of folic acid and lamotrigine therapy in some rodent models of epilepsy and behaviour

It has been suggested that a folic acid (FA) deficiency induced by antiepileptic drugs might be the basis for the neuropsychiatric toxicity associated with these drugs. In the present study, lamotrigine (LTG), one of the newer antiepileptic drugs, was evaluated for its effect on epilepsy, mood and memory in mice. Further, the effect of the addition of FA to LTG therapy was also investigated. The increasing current electroshock seizure test was used to evaluate the anticonvulsant effect of drugs, while the forced swimming test (FST) and spontaneous alternation behaviour (SAB) models were employed for assessing the effects on mood and memory, respectively. LTG exhibited a dose-dependent increase in seizure threshold, whereas FA did not have any effect. LTG did not affect, whereas FA decreased, behavioural depression in the FST in mice. Neither LTG nor FA affected memory scores in the SAB test. The combination of LTG and FA significantly reduced depression while enhancing the effects on memory and seizure threshold. The present observations have confirmed the antiepileptic action of LTG in yet another rodent model of epilepsy. Further, the results clearly demonstrate the additional benefits on epilepsy, mood and memory brought about by the inclusion of FA in the LTG regimen.

Effects of lamotrigine and levetiracetam on seizure development in a rat amygdala kindling model

In kindling models of epilepsy, the period during which repeated stimulation evokes intensifying seizures is attributed to an underlying epileptogenic process, and the point at which class 5 kindled seizures occur is considered the established epileptic state. Previous studies have indicated that a separation can occur between drug effects on these two components. For example, carbamazepine and phenytoin inhibit kindled seizures but have no effect on seizure development, whereas levetiracetam inhibits both components. We have investigated the profile of lamotrigine in the amygdala kindling model, including levetiracetam for comparison. As expected, both treatments dose-dependently inhibited class 5 kindled seizures. In a separate study, daily administration of either lamotrigine (20mgkg(-1) i.p.) or levetiracetam (50mgkg(-1) i.p.) demonstrated antiepileptogenic-like effects by blocking seizure development during the treatment period. Following cessation of drug treatment, further daily stimulation resulted in kindled seizure development, though there was a significant increase with both treatment groups, relative to the control group, in the total number of stimulations required to produce classes 3 and 5 seizures. In addition, prior levetiracetam treatment appeared to delay or prevent the expected increase in after-discharge duration (ADD). These results suggest that lamotrigine, like levetiracetam, possesses the ability to counteract kindling acquisition, which differentiates it from other drugs with sodium channel blocking activity.

Neuroprotective activity of CHF3381, a putative N-methyl-D-aspartate receptor antagonist

The aim of this study was to evaluate the neuroprotective effect of CHF3381, a novel putative NMDA antagonist characterized by a good therapeutic index. We have compared the effects of CHF3381 on kainate seizure-induced neurodegeneration with those produced by the non competitive NMDA receptor antagonist MK-801 and by the Na channel blocker lamotrigine. All compounds have been employed at doses incapable of preventing or attenuating seizures. The fluorescent marker Fluoro-Jade B has been used to identify degenerating cells. Animals pretreated with lamotrigine presented the same degree of cell damage as the controls. As for the controls, a clear correlation was also observed between seizure severity and neurodegeneration. In contrast, MK-801 and CHF3381 completely prevented cell damage. These data indicate that CHF3381 may be successfully utilized in neurological disorders characterized by or associated with neurodegenerative excitotoxicity.

Synergistic interaction between valproate and lamotrigine against seizures induced by 4-aminopyridine and pentylenetetrazole in mice

We compared the effects of adding a non-protective dose of valproate to increasing doses of lamotrigine with those of monotherapy and vice versa in CD1 mice. Anticonvulsant effects were evaluated against seizures induced by both 4-aminopyridine and pentylenetetrazole, and neurotoxic effects were evaluated by the rotarod test. Changes in anticonvulsants, gamma-aminobutyric acid (GABA) and glutamate concentrations in the whole brain were also assessed. Lamotrigine increased the potency ratio of valproate against 4-aminopyridine and pentylenetetrazole but not on rotarod, the protective index being increased from 1.1 to 2.4 against 4-aminopyridine and from 1.9 to 3.8 against pentylenetetrazole, without changes in brain valproate, and with a significant increase in brain GABA. Valproate increased the potency ratio of lamotrigine against 4-aminopyridine but not on rotarod, the protective index being increased from 4.4 to 7.3; valproate also increased brain lamotrigine (but only at low doses), brain GABA and brain glutamate. In conclusion, non-protective doses of lamotrigine increased the therapeutic index of valproate and vice versa, and these effects appeared to be pharmacodynamic.

Influence of administration vehicles and drug formulations on the pharmacokinetic profile of lamotrigine in rats

Given that administration vehicles and drug formulations can affect drug bioavailability, their influence on the pharmacokinetic profile of lamotrigine (LTG), a new-generation anti-epileptic drug, was studied in rats. Three different formulations administered intraperitoneally at a dose of 10 mg/kg were used: (1) LTG suspended in a 0.25% methylcelulose solution, (2) LTG dissolved in a 50% propylene glycol solution, and (3) LTG isethionate dissolved in distilled water. Plasma and brain homogenate levels were determined in order to evaluate vehicle-dependent drug absorption. The results demonstrated rapid absorption of LTG when it was administered as an aqueous solution, in contrast to a slower and more erratic absorption after the injection of either the lipophilic solution or the suspension. A plasma peak was achieved 15 min post-dose with the aqueous solution, with a brain peak being achieved 15 min later, while with the other formulations both plasma and brain homogenate peaks were reached 2 h after LTG administration. This study suggests that LTG isethionate dissolved in distilled water is the most suitable formulation for successful LTG pharmacokinetic studies in rats.

Neocortical potassium currents are enhanced by the antiepileptic drug lamotrigine

PURPOSE

We used field-potential recordings in slices of rat cerebral cortex along with whole-cell patch recordings from rat neocortical cells in culture to test the hypothesis that the antiepileptic drug (AED) lamotrigine (LTG) modulates K+-mediated, hyperpolarizing currents.

METHODS

Extracellular field-potential recordings were performed in neocortical slices obtained from Wistar rats aged 25-50 days. Rat neocortical neurons in culture were subjected to the whole-cell mode of voltage clamping under experimental conditions designed to study voltage-gated K+ currents.

RESULTS

In the in vitro slice preparation, LTG (100-400 microM) reduced and/or abolished epileptiform discharges induced by 4-aminopyridine (4AP, 100 microM; n = 10), at doses that were significantly higher than those required to affect epileptiform activity recorded in Mg2+-free medium (n = 8). We also discovered that in cultured cortical cells, LTG (100-500 microM; n = 13) increased a transient, 4AP-sensitive, outward current elicited by depolarizing commands in medium containing voltage-gated Ca2+ and Na+ channel antagonists. Moreover, we did not observe any change in a late, tetraethylammonium-sensitive outward current.

CONCLUSIONS

Our data indicate that LTG, in addition to the well-known reduction of voltage-gated Na+ currents, potentiates 4AP-sensitive, K+-mediated hyperpolarizing conductances in cortical neurons. This mechanism of action contributes to the anticonvulsant effects exerted by LTG in experimental models of epileptiform discharge, and presumably in clinical practice.