Remacemide HCl and its metabolite, FPL 12495AA, limit action potential firing frequency and block NMDA responses of mouse spinal cord neurons in cell culture

Isobolographic analysis of interactions between remacemide and conventional antiepileptic drugs in the mouse model of maximal electroshock

Using the mouse maximal electroshock-induced seizure model, indicative of tonic-clonic seizures in humans, the present study was aimed at characterizing the interaction between remacemide and valproate, carbamazepine, phenytoin, and phenobarbital. Isobolographic analysis indicated additive interactions between remacemide and valproate, carbamazepine, and phenytoin (for all fixed ratios of tested drugs: 1:3, 1:1, and 3:1). Additivity was also observed between remacemide and phenobarbital applied in proportions of 1:1 and 3:1. In contrast, the combination of remacemide and phenobarbital at the fixed-ratio of 1:3 resulted in antagonism. Neither motor performance nor long-term memory was impaired by remacemide or by carbamazepine, phenobarbital, phenytoin, and valproate whether or not these drugs were administered singly or in combination. In combination with remacemide, brain concentrations of carbamazepine, phenobarbital, and phenytoin were increased by 71, 21, and 16%, respectively. Although brain valproate concentrations were unaffected by remacemide co-administration, brain concentrations of remacemide and its active metabolite, desglycinyl-remacemide, were increased by 68 and 162%, respectively. In contrast, phenobarbital co-administration was associated with decreases in brain remacemide (27%) and desglycinyl-remacemide (9%) concentrations, whereas only remacemide concentrations (increased by 131%) were affected by carbamazepine co-administration. In conclusion, significant and desirable pharmacodynamic interactions were observed between remacemide and valproate, carbamazepine, phenytoin, and phenobarbital. However, the concurrent pharmacokinetic interactions associated with remacemide complicate these observations and do not make remacemide a good candidate for adjunctive treatment of epilepsy.

Inhibition of sustained repetitive firing in cultured hippocampal neurons by an aqueous fraction isolated from Delphinium denudatum

In this report we investigated the effects of the aqueous fraction (AF) isolated from Delphinium denudatum on sustained repetitive firing in cultured neonatal rat hippocampal pyramidal neurons. Blockade of SRF is one of the basic mechanisms of antiepileptic drugs (AED) at the cellular level. The effects of aqueous fraction (0.2-0.6 mg/ml) were compared with the prototype antiepileptic drug, phenytoin (PHT). Using the whole cell current-clamp technique, sustained repetitive firing was elicited in neurons by a depolarizing pulse of 500 ms duration, 0.3 Hz and 0.1-0.6 nA current strength. Similar to phenytoin, aqueous fraction reduced the number of action potentials (AP) per pulse in a concentration-dependent manner until no action potentials were elicited for the remainder of the pulse. There was a corresponding use-dependent reduction in amplitude and Vmax (velocity of upstroke) of action potentials. The Vmax and amplitude of the first action potential was not affected by phenytoin, while aqueous fraction exhibited concentration-dependent reduction. At 0.6 mg/ml aqueous fraction reduced Vmax to 58-63% and amplitude to 16-20% of the control values. The blockade of sustained repetitive firing by aqueous fraction was reversed with hyperpolarization of membrane potential (-65 to -75 mV) while depolarization of membrane potential (-53 to -48 mV) potentiated the block. The results suggest that aqueous fraction blocks sustained repetitive firing in hippocampal neurons in a use-dependent and voltage-dependent manner similar to phenytoin. However, unlike phenytoin, which interacts preferably with the inactive state of the Na+ channel, the compounds present in aqueous fraction apparently also interact with the resting state of the Na+ channels as suggested by dose-dependent reduction of Vmax and amplitude of first AP. We conclude that aqueous fraction contains potent anticonvulsant compounds.

Lamotrigine and remacemide protect striatal neurons against in vitro ischemia: an electrophysiological study

In the present study, we investigated the cellular and synaptic mechanisms underlying the neuroprotective action of lamotrigine and remacemide. Both drugs, in fact, have been reported to exert a neuroprotective action in in vivo animal models of ischemia. To address this issue, electrophysiological recordings and cell swelling measurements were performed from striatal neurons in control condition and during combined oxygen and glucose deprivation (in vitro ischemia) in a brain slice preparation. Lamotrigine, remacemide, and the active desglycinyl metabolite of remacemide, D-REMA, induced a concentration-dependent reduction of both repetitive firing discharge and excitatory postsynaptic potentials. However, while remacemide and D-REMA exerted their inhibitory action on glutamatergic transmission by blocking NMDA receptors, lamotrigine exerted a preferential presynaptic action, as indicated by its ability to increase paired-pulse facilitation. Both remacemide and lamotrigine were found to be neuroprotective against the irreversible field potential loss and cell swelling induced by in vitro ischemia, and coadministration of low concentrations of these drugs exerted an additive neuroprotective action. A combined use of lamotrigine and remacemide could be employed in clinical trials to enhance neuroprotection in neurological disorders involving an abnormal striatal glutamatergic transmission.

Effects of remacemide in two models of genetically determined generalized epilepsy, the GAERS and the audiogenic Wistar AS

The antiepileptic effects of remacemide were assessed in two models of genetically determined generalized epilepsy. The model of non-convulsive epilepsy used was a model of absence seizures, the GAERS (genetic absence epilepsy rats from Strasbourg), and the model of convulsive seizures was an audiogenic rat model, the Wistar AS. In the eight GAERS studied, the three doses of remacemide (20, 40, and 80 mg/kg) dose-dependently reduced the expression of spike-and-wave discharges (SWDs) that had almost totally disappeared at the highest dose used, 80 mg/kg. However, at the latter dose, the effect of remacemide may be partly due to a change in the vigilance level of the animals. In the Wistar AS, the dose of 20 mg/kg prolonged by twofold the latencies to wild running and tonic seizures, and prevented their expression in one rat out of the eight studied. At 40 mg/kg, the expression of wild running and tonic seizures was inhibited in seven and maintained in one of the eight rats studied. The present results support the effects of remacemide in tonic/clonic seizure, which was the first target of the drug, and confirm the effect of the anticonvulsant on absence seizures.

Voltage-gated sodium channels in epilepsy

Animal experiments, and particularly functional investigations on human chronically epileptic tissue as well as genetic studies in epilepsy patients and their families strongly suggest that some forms of epilepsy may share a pathogenetic mechanism: an alteration of voltage-gated sodium channels. This review summarizes recent data on changes of sodium channel expression, molecular structure and function associated with epilepsy, as well as on the interaction of new and established antiepileptic drugs with sodium currents. Although it remains to be determined precisely how and to what extent altered sodium-channel functions play a role in different epilepsy syndromes, future promising therapy approaches may include drugs modulating sodium currents, and particularly substances changing their inactivation characteristics.

Influence of cytochrome P450 induction on the pharmacokinetics and pharmacodynamics of remacemide hydrochloride

Remacemide hydrochloride (RMD) is a putative anticonvulsant agent with an active metabolite, desglycinyl-remacemide (DGR) and a broad spectrum of activity in experimental seizure models. In clinical trials, however, the efficacy of RMD is questionable. In the case of add-on studies, the inconclusive findings may be related to pharmacokinetic interactions between RMD and established antiepileptic drugs. We have investigated the influence of cytochrome P450 (CYP(450)) induction following repeated treatment with phenobarbital (PB) on the pharmacokinetics and pharmacodynamics of RMD in mice. Pre-treatment with PB (80 mg/kg; once daily for 4 days) significantly increased CYP(450) content and activity in mouse liver. This was associated with a consistent reduction in the brain concentrations of both RMD and DGR and attenuation of the anticonvulsant effects of RMD in the maximal electroshock model. Pharmacokinetic analysis suggested that DGR was proportionately more susceptible to CYP(450) induction than the parent compound. As the principal active moiety, the selectively enhanced metabolism of DGR under induced conditions may underlie the debatable findings of add-on trials with RMD in refractory epilepsy. However, this hypothesis does not explain the similarly questionable efficacy of RMD monotherapy in newly diagnosed epilepsy, an observation that may have wider pharmacological implications.

Differential effects of remacemide and desglycinyl-remacemide on epileptiform burst firing in the rat hippocampal slice

Remacemide is a potential anticonvulsant drug with an active metabolite, desglycinyl-remacemide (DGR). Both moieties have been reported to block neuronal Na(+) channels and the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor. The effects of remacemide and DGR on zero Mg(2+)/4-aminopyridine-induced epileptiform discharges were investigated in the rat hippocampal slice preparation and compared with carbamazepine (CBZ), a prototypic Na(+) channel blocker, and AR-R15896AR, a putative NMDA channel blocker. Remacemide (0-100 microM) was without significant effect, while DGR, CBZ and AR-R15896AR all decreased burst frequency in a concentration (0-100 microM) dependent manner. These findings suggest that remacemide is not sufficiently potent at the Na(+) channel or NMDA receptor to attenuate epileptiform activity in this model and that the anticonvulsant effects of the drug may be mediated by DGR.

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

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

Simultaneous determination of remacemide hydrochloride and desglycinylremacemide (AR-R12495XX) in brain tissue by high-performance liquid chromatography

Remacemide hydrochloride, a novel anticonvulsant agent, and its major active metabolite, desglycinylremacemide, were measured simultaneously in brain tissue by high-performance liquid chromatography with UV detection. Intra- and inter-assay variations for remacemide (1, 5, 10 microg/ml) were 5.1, 10.5 and 3.1% and 3.1, 4.0 and 1.3%, respectively. Intra- and inter-assay variations for desglycinylremacemide (1, 5, 10 microg/ml) were 4.2, 3.8 and 8.4% and 7.9, 8.8 and 3.1%, respectively. Limits of detection and quantification for both analytes were 4 and 31 ng/ml, respectively, with recovery consistently > or =85%. This reliable assay has applications in the pre-clinical neuropharmacokinetic and neuropharmacodynamic investigation of remacemide hydrochloride.

The anticonvulsant remacemide and its metabolite AR-R12495AA attenuate spinal synaptic transmission and carrageenan-induced inflammation in the young rat

The effects of the anticonvulsants remacemide [(+/-)-2-amino-N-(1-methyl-1,2-diphenylethyl)-acetamide hydrochloride] and its des -glycinated metabolite AR-R12495AA [(+/-)-1-methyl-1,2-diphenylethylamine- monohydrochloride] on primary afferent-induced synaptic transmission and frequency-dependent summation of synaptic potentials were assessed in the young rat spinal cord in vitro. Behavioural studies in the rat determined the effects of these anticonvulsant compounds in the carrageenan model of inflammation. Recordings of the extracellular dorsal root-evoked ventral root potential (DR-VRP) revealed a significant reduction of the duration and t(1)-(2)decay of the long latency, slow DR-VRP by remacemide (50 and 100 microM) and AR-R12495AA (25, 50 and 100 mM). The short-latency, fast monosynaptic DR-VRP peak was reduced by only the highest concentration of AR-R12495AA (100 microM). In intracellular dorsal root-evoked excitatory postsynaptic potentials (DR-EPSPs) of single ventral horn neurons, AR-R12495AA (100 microM) attenuated the time course of the long-latency (slow) EPSP. Frequency-dependent (0.5-2.0 Hz) summation of dorsal root-evoked synaptic events (recorded extracellularly as the cumulative ventral root depolarization (CVRD), and intracellularly as wind-up) was attenuated by remacemide (100 microM) and AR-R12495AA (50 and 100 microM). Pre-treatment with intra-peritoneal injection of 75 mg/kg of remacemide or AR-R12495AA caused a significant reduction of carrageenan-induced mechanical hyperalgesia and oedema. These electrophysiological and behavioural data provide evidence that remacemide and AR-R12495AA may also possess analgesic and anti-inflammatory activity.

Remacemide: current status and clinical applications

Remacemide (RMC) is a non-competitive, low-affinity N-methyl-D-aspartate (NMDA) receptor antagonist that does not cause the behavioural and neuropathological side effects seen with other NMDA receptor antagonists. RMC and its active metabolite, AR-R 12495 AR, which has moderate affinity for the NMDA receptor, also interact with voltage-dependent neuronal sodium channels. Both agents show efficacy in a variety of animal models of epilepsy, parkinsonism and cerebral ischaemia. There is no evidence for teratogenicity or genotoxicity. RMC delays the absorption of L-dopa and elevates the concentrations of drugs metabolised by the hepatic cytochrome P450 3A4 isoform. RMC and AR-R 12495 AR have moderate protein binding and linear pharmacokinetics. Controlled studies show evidence of efficacy in treating epilepsy and Parkinson's disease. Post-surgical outcomes in RMC-treated patients at risk for intra-operative cerebral ischaemia are also encouraging. Adverse effects are related to the gastrointestinal and central nervous systems. RMC is a promising drug with numerous potential applications for both acute or chronic conditions associated with glutamate-mediated neurotoxicity.

New anti-epileptic drugs

Epilepsy represents the most common serious neurological disorder, with a prevalence of 0.4 - 1%. Approximately 30% of patients are resistant to currently available drugs. New anti-epileptic drugs are needed to treat refractory epilepsy, improve upon current therapies, improve the prognosis of epilepsy and to prevent the epileptogenic process. Designing compounds with specific physiological targets would seem the most rational method of anti-epileptic drug development, but results from this approach have been disappointing; the widespread screening of compounds in animal models has been much more fruitful. Older methods of animal screening have used acute seizure models, which bear scant relationship to the human condition. More modern methods have included the development of animal models of chronic epilepsy; although more expensive, it is likely that these models will be more sensitive and more specific in determining anti-epileptic efficacy. In this review, we consider the possible physiological targets for anti-epileptic drugs, the animal models of epilepsy, problems with clinical trials and ten promising anti-epileptic drugs in development (AWD 131-138, DP16 (DP-VPA), ganaxolone, levetiracetam, losigamone, pregabalin, remacemide, retigabine, rufinamide and soretolide). Perhaps the most important advances will come about from the realisation that epilepsy is a symptom, not a disease. Preclinical testing should be used to determine the spectrum of epilepsies that a drug can treat, and to direct later clinical trials, which need to select patients based on carefully defined epilepsy syndromes and aetiologies. Not only will such an approach improve the sensitivity of clinical trials, but also will lead to a more rational basis on which to treat.

Neuroprotective effect of remacemide hydrochloride in a perforant pathway stimulation model of status epilepticus in the rat

Previous studies have demonstrated that remacemide and its desglycinyl metabolite, AR-R 2495AA, reduce neuronal damage in animal models of ischemia, subarachnoid hemorrhage, and traumatic brain injury. The aim of the present study was to investigate whether remacemide hydrochloride also alleviates seizure-induced neuronal damage in a model of status epilepticus induced by the stimulation of the perforant pathway (PP) in the rat. Chronic oral remacemide treatment (3 x 25 mg/kg/day) was started either 2 days before or 2 h after the beginning of PP stimulation (2 mA, 20 Hz, 0.1 ms pulse duration for 60 min). The effects of remacemide treatment on the severity of seizures, electroencephalogram (EEG) parameters, seizure-induced neuronal damage in the temporal lobe regions, and memory impairment were compared to unstimulated and stimulated vehicle-treated controls, and carbamazepine-pre-treated (3 x 40 mg/kg/day) rats. Both remacemide and carbamazepine pretreatments, but not remacemide posttreatment, decreased pyramidal cell damage in the CA3 and CA1 subregions of the hippocampus (P < 0.05). In addition, overall neuronal damage in the extrahippocampal temporal lobe regions (the piriform cortex, entorhinal cortex, and the amygdaloid complex) was milder in remacemide-pretreated rats compared to stimulated control rats (P < 0.01). The neuroprotective effect was most evident on the side contralateral to stimulation. Remacemide or carbamazepine pretreatment had no evident effect on the number or duration of behavioral seizures during PP stimulation. Neither drug altered the spectral parameters of the baseline EEG or prevented status epilepticus-induced EEG slowing observed 2 weeks after PP stimulation. Nor did remacemide or carbamazepine treatment alleviate spatial memory impairment determined in a Morris water-maze task 2 weeks after PP stimulation. Our data provide evidence that pretreatment with remacemide has a moderate neuroprotective effect against status epilepticus-induced neuronal damage.

Effects of anti-epileptic drugs on glutamine synthetase activity in mouse brain

1. Glutamine synthetase (GS) is a key enzyme in the regulation of glutamate neurotransmission in the central nervous system. It is responsible for the conversion of glutamate to glutamine, and for the detoxification of ammonia. 2. We have investigated the effects of single and repeated intraperitoneal administration of a range of established and new anti-epileptic drugs on GS activity in mouse brain. 3. Four hours after the final dose, animals were sacrificed and the brains removed for analysis of GS activity. 4. Both single and repeated doses of phenytoin and carbamazepine were found to reduce enzyme activity (P<0.05). 5. Single doses of phenobarbitone, felbamate and topiramate were without effect, however repeated administration of these drugs dose-dependently reduced GS activity (P<0.05). 6. Single and repeated doses of sodium valproate, vigabatrin, lamotrigine, gabapentin, tiagabine, levetiracetam and desglycinyl-remacemide were found to have no effect on GS activity. 7. The reduction in enzyme activity demonstrated is unlikely to be related to the anti-epileptic actions of these drugs, but may contribute to their toxicity.

An active-control trial of lamotrigine monotherapy for partial seizures

OBJECTIVE

We report the results of a double-blind, double-dummy, active-control study designed to evaluate the efficacy and safety of lamotrigine (LTG) administered as monotherapy to adult outpatients with partial seizures.

BACKGROUND

The effectiveness of LTG as add-on therapy for partial seizures in adults has previously been established.

METHODS

After an 8-week baseline during which patients continued their baseline antiepileptic drug (carbamazepine or phenytoin monotherapy), 156 patients were randomly assigned to receive increasing doses of LTG (target 250 mg b.i.d.) or valproic acid (VPA; target low dose of 500 mg b.i.d.) during the first 4 weeks of an 8-week transition period. Carbamazepine or phenytoin was withdrawn over the next 4 weeks; then patients entered a 12-week monotherapy period. Study drug treatment was discontinued in patients who met predetermined escape criteria for seizure worsening.

RESULTS

More patients receiving LTG were successfully maintained on monotherapy compared with patients receiving VPA (56% versus 20%; p < 0.001). The time to meet the escape criteria was also significantly longer in LTG-treated patients (median = 168 days) than in VPA-treated patients (median = 57 days; p = 0.001). The incidence of adverse events during the monotherapy period was lower than during the transition period. Four LTG patients and five VPA patients reported serious adverse events. Two of those patients experienced a rash that led to withdrawal soon after adding LTG to carbamazepine.

CONCLUSIONS

We conclude that LTG is effective and well tolerated when administered as monotherapy in adult patients with partial seizures.

Cost-effectiveness model of adjunctive lamotrigine for the treatment of epilepsy

OBJECTIVE

To predict the cost-effectiveness of lamotrigine by evaluating the costs and health outcomes in treated patients.

BACKGROUND

Lamotrigine adjunctive therapy has been found to be associated with decreased seizure frequency and severity in patients who are refractory to treatment with the older antiepileptic drugs (AEDs).

METHODS

We used a cost-effectiveness clinical decision analysis framework to assess the impact of these clinical benefits on patient health care use. The measure of effectiveness was seizure-free days gained. The measures of health care resource use included hospitalizations, outpatient and emergency department visits, surgery, and AEDs. Medical care use and cost estimates were derived from clinical trial data and published sources. Costs and effectiveness (incremental costs per seizure-free days gained) of lamotrigine adjunctive therapy versus older AEDs were compared in patients refractory to previous treatment during three time periods: the start-up year, the second year when decisions about surgery were made, and all subsequent years.

RESULTS AND CONCLUSIONS

The model predicts that use of lamotrigine would be associated with an overall reduction in use of other direct medical care resources (hospitalizations, outpatient visits, diagnostic and laboratory tests, and surgery). For a 10-year time horizon, the estimated cost-effectiveness ratio is $6.9 per seizure-free day gained. The model provides a flexible framework to analyze the effect of new antiepileptic drugs.

Anticonvulsant activity and interactions with neuronal voltage-dependent sodium channel of analogues of ameltolide

Fifteen compounds related to ameltolide (LY 201116) were studied for (i) anticonvulsant potential in the maximal electroshock-induced seizures (MES) and the subcutaneous pentylenetetrazol (sc Ptz) tests in mice and rats and (ii) interactions with neuronal voltage-dependent sodium channels. Compounds were chosen ranging in anticonvulsant activity in mice from very active to inactive. The active compounds were defined as those protecting 50% of the animals at doses between 10 and 50 micromol/kg and inactive compounds as those protecting 50% of the animals at doses greater than 1 mmol/kg. The series studied included three N-(2,6-dimethylphenyl)benzamides (compounds 1, 2 (ameltolide), and 3), three N-(2,2,6, 6-tetramethyl)piperidinyl-4-benzamides (compounds 4, 5, 6), one phenylthiourea (compound 7), five N-(2,6-dimethylphenyl)phthalimides (compounds 8, 9, 10, 13, and 14), two N-phenylphthalimide derivatives (compounds 11 and 12), and one N-(2,2,6, 6-tetramethyl)piperidinyl-4-phthalimide (compound 15). Phenytoin (PHT) was employed as the reference prototype antiepileptic drug. After inital screening in mice, compounds 1, 2, 3, 5, 8, 9, 10, 13, and 14 were selected for further testing in rats. Anticonvulsant ED50s (effective doses in at least 50% of animals tested) of compounds in the MES test were determined in rats dosed orally and amounted to 52 (1), 135 (2), 284 (3), 231 (8), 131 (9), 25 (10), 369 (13), 354 (14), and 121 (PHT) micromol/kg, compound 5 presenting with an ED50 value higher than 650 micromol/kg. In our hands, the apparent IC50s (inhibitory concentrations 50) of compounds toward binding to rat brain synaptosomes of [3H]batrachotoxinin-A-20alpha-benzoate were 0.25 (1), 0.97 (2), 0.35 (3), 25.8 (5), 161.3 (8), 183.5 (9), 0.11 (10), 1.86 (13), 47.8 (14), and 0.86 (PHT) microM. The relationship between the activity in the MES test and the capacity to interact in vitro with neuronal voltage-dependent sodium channels and the fact that the IC50 values obtained in the in vitro test are close to the brain concentrations at which anticonvulsant activities are reported to occur for ameltolide strongly suggest that the anticonvulsant properties of most compounds tested could be a direct result of their interaction with the neuronal voltage-dependent sodium channel.

Neurochemical actions of the desglycinyl metabolite of remacemide hydrochloride (ARL 12495AA) in mouse brain

1. Remacemide hydrochloride, a recently developed antiepileptic drug, is believed to exert its effects, at least in part, via its desglycinyl metabolite, ARL 12495AA. 2. We have investigated the effects of ARL 12495AA on several neurochemical parameters in mouse brain. Adult male ICR mice were randomized into two groups and administered ARL 12495AA (0-75 mg kg-1) intraperitoneally, either as a single dose or once daily for 5 days. 3. Six hours after the final dose, animals were killed and their brains removed. Brain tissues were analysed for concentrations of gamma-aminobutyric acid (GABA), glutamine and glutamate and for the activities of GABA-transaminase (GABA-T) and glutamic acid decarboxylase (GAD). 4. Single dose ARL 12495AA was without effect on any of the parameters investigated. 5. Repeated ARL 12495AA treatment did not alter brain concentrations of GABA and glutamine, but at a high dose there was a trend toward reduced brain glutamate concentrations (P = 0.10). 6. Repeated administration of ARL 12495AA at a high dose significantly increased GABA-T activity (P < 0.05) and decreased that of GAD (P < 0.05). 7. These findings may have relevance to the clinical use of remacemide hydrochloride in human epilepsy.

Electrophysiological effects of the anticonvulsant remacemide hydrochloride and its metabolite ARL 12495AA on rat CA1 hippocampal neurons in vitro

The electrophysiological actions of the putative anticonvulsants remacemide hydrochloride and its des-glycine metabolite ARL 12495AA were examined using whole-cell recordings from CA1 hippocampal neurons in adult rat brain in vitro. Remacemide hydrochloride (4-400 microM) and ARL 12495AA (4-400 microM) limited sustained high frequency repetitive firing (SRF) induced by application of long duration depolarizing current pulses (20-400 pA, 500 msec). This SRF limitation was concentration-dependent, and equipotent IC50 values of 66 and 60 microM were calculated for remacemide hydrochloride and ARL 12495AA, respectively. Examination of the spike configuration revealed that, over the same concentration range, each compound caused a concentration-related reduction of: (a) the action potential amplitude; and (b) the rate-of-rise. Remacemide hydrochloride or ARL 12495AA increased spike duration and decreased or eliminated the spike after-hyperpolarization. Possible mechanisms for these electrophysiological actions including modulation of sodium and/or potassium channel activity are considered. It is suggested that such multiple mechanisms, including inhibition of SRF may be relevant to the anticonvulsant properties of remacemide hydrochloride and its metabolite, ARL 12495AA. The activity of both compounds as modulators of neuronal excitability indicates that metabolic conversion of remacemide hydrochloride to ARL 12495AA could enhance the therapeutic efficacy of the former.

Remacemide hydrochloride: a novel antiepileptic agent

1. Remacemide hydrochloride has been shown to possess anticonvulsant activity in a wide range of animal models of epilepsy with ED50s in the 6-60 mg/kg range, depending on the species and route of administration. The compound also has been shown to be effective clinically as add-on therapy for partial seizures. 2. Degradation of remacemide yields the desglycinated metabolite that is approximately 2-fold more potent as an anticonvulsant agent than the parent drug. 3. Both compounds displace [3H]MK801 binding from the cerebral cortical membranes, and the metabolite is approximately 150-fold more potent in doing so than remacemide. This effect, together with the findings that the desglycinate reduces N-methyl-D-aspartate (NMDA)-induced depolarizations in a variety of preparations, suggests that the mechanism of action is through blockade of the channel site of the NMDA-receptor complex. 4. Remacemide and its metabolite, in common with other antiepileptic agents, block sustained repetitive-firing in cultured neurons. The metabolite also has been shown to decrease glutamate release from cortical slices. 5. Remacemide hydrochloride has neuroprotective properties when tested on models of cerebral ischemia. 6. The drug has low toxicity in contrast to other NMDA-channel-blocking compounds, such as MK801 and phencyclidine, probably because of its low affinity for the channel-binding site.

Remacemide hydrochloride and ARL 15896AR lack abuse potential: additional differences from other uncompetitive NMDA antagonists

This study was designed to determine the possible abuse liability and phencyclidine-like effects of the low-affinity uncompetitive N-methyl-D-aspartate (NMDA) antagonists remacemide hydrochloride [(+/-)-2-amino-N-(1-methyl-1,2-diphenylethyl)-acetamine hydrochloride] and ARL 15896AR [(+)-alpha-phenyl-2-pyridine-ethanamine dihydrochloride]. For the abuse-liability studies, in rats trained to self-administer cocaine intravenously (0.1 mg/kg/injection), doses of remacemide HCl, ARL 15896AR, phencyclidine, and saline were made available, and the number of injections self-administered was recorded. In different sets of rats, we assessed the ability of these drugs to induce phencyclidine-like stereotyped behavior. Doses of the compounds were expressed as multiples of the 50% effective dose (ED50), as determined from the maximal electroshock (MES) test by using either oral or intravenous administration. None of the remacemide hydrochloride or ARL 15896AR doses was self-administered at a level higher than that of the saline vehicle, unlike cocaine and phencyclidine, which were self-administered at high and moderate levels, respectively. Unlike that with remacemide hydrochloride and ARL 15896AR, oral administration of the high-affinity uncompetitive NMDA receptor-antagonists phencyclidine, ARL 16247 [N-(3-ethylphenyl)-N-methyl-N'-naphthylguanidine] and MK-801 engendered phencyclidine-like stereotypy at doses near their MES ED50 values. These data confirm the unusual safety of remacemide hydrochloride and ARL 15896AR and demonstrate that they do not possess reinforcing properties. As such, they are unlikely to present a drug-abuse problem in human beings.