The anticonvulsant effects of the enantiomers of losigamone

Tetramic and tetronic acids: an update on new derivatives and biological aspects

Significant developments in the isolation of tetramic acids and tetronic acids, in the elucidation of their biosyntheses and their biological activities and in laboratory syntheses are reviewed with a focus on those derivatives with medicinal and pharmacological relevance. Important new members of the title compound families isolated since the year 2000 are covered as well as new biological aspects of some earlier congeners.

Interactions between two enantiomers of losigamone and conventional antiepileptic drugs in the mouse maximal electroshock model--an isobolographic analysis

The aim of this study was the isobolographic evaluation of interactions between two enantiomers of losigamone, AO-242 [(+)-5(R)-alpha(S)-5-(2-chlorophenylhydroxymethyl)-4-methoxy-2(5H)-furanone] and AO-294 [(-)-5(S)-alpha(R)-5-(2-chlorophenylhydroxymethyl)-4-methoxy-2(5H)-furanone], and valproate, carbamazepine, phenytoin, or phenobarbital in the maximal electroshock test in mice. Both enantiomers interacted additively with conventional antiepileptic drugs at all studied fixed dose ratios (1:3, 1:1, 3:1). Furthermore, AO-242, AO-294 and antiepileptics applied alone, as well as combinations of enantiomers and antiepileptics did not affect motor performance in the chimney test. Significant impairment of long-term memory (passive-avoidance task) was noted only in the case of valproate alone, given at the dose equal to its median effective dose (ED(50)) against maximal electroshock. All other antiepileptics and their combinations with AO-242 or AO-294 did not impair memory of mice. Enantiomers did not affect the brain concentrations of antiepileptic drugs, indicating a pharmacodynamic nature of the observed interactions. In conclusion, the present results suggest both AO-242 and AO-294 as promising candidate drugs in the add-on therapy of refractory epilepsy.

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

The aim of this study was the isobolographic evaluation of interactions between losigamone (LSG), valproate (VPA), carbamazepine (CBZ), phenytoin (PHT), and phenobarbital (PB) in the maximal electroshock (MES) test in mice. Electroconvulsions were produced by means of an alternating current (ear-clip electrodes, 0.2-s stimulus duration, and tonic hindlimb extension taken as the endpoint). Adverse effects were evaluated in the chimney test (motor coordination) and the passive avoidance task (long-term memory). Brain concentrations of antiepileptic drugs (AEDs) were measured by immunofluorescence or high-performance liquid chromatography. Isobolographic analysis indicated synergistic interactions between LSG and VPA. For example, in the proportion of 1:1 the theoretically calculated 50% effective dose for additivity (ED(50add)) was 138 mg/kg, while the experimentally derived ED(50) for the mixture (ED(50mix)) was 85.2 mg/kg. The difference was significant at p<0.001. LSG combined with CBZ or PHT showed additivity, whereas the combinations of LSG with PB were either additive, for the fixed ratios of 1:3 and 1:1, or antagonistic for the ratio of 3:1 (ED(50add)=18.4 mg/kg versus ED(50mix)=26.7 mg/kg, p<0.05). Impairment of long-term memory was noted only in the case of VPA given at its ED(50), however this AED did not affect motor performance. LSG, CBZ, PHT and PB (applied at their ED(50) values) and co-administration of LSG with conventional AEDs (including VPA) impaired neither motor performance nor long-term memory. LSG did not affect the brain concentration of VPA or PB, but significantly elevated the brain concentrations of CBZ and PHT. In contrast, VPA, CBZ and PHT significantly increased the brain concentration of LSG, indicating a pharmacokinetic contribution to the observed pharmacodynamic interactions. Although LSG exhibited some favorable pharmacodynamic interactions with various AEDs, these were complicated by pharmacokinetic interactions and emphasize the importance of measuring AED concentrations in studies designed to identify desirable AED combinations.

Novel anticonvulsant medications in development

Epilepsy is currently the most prevalent neurological disorder worldwide. Pharmacological therapy remains the cornerstone of epilepsy treatment, however, refractory epilepsy is still a significant clinical problem despite the release of the second generation of anticonvulsants. Anticonvulsant treatment failures may result from lack of efficacy and presence of significant side effects. One rationale for incomplete effectiveness of the currently available anticonvulsants is that they were identified using the same classical models and therefore work largely by the same actions. These mechanisms fail to consider variations in the pathophysiological process that results in epilepsy, nor have they been shown to prevent the process of developing epilepsy (epileptogenesis). The next generation of anticonvulsants has taken into account the shortcomings of existing agents and attempted to improve on the currently available treatments using rationale drug design. This group of investigational anticonvulsants may be broadly classified as possessing one or more of the following: 1) increased tolerability through improvement in drug chemical structure or better delivery to the site of action, 2) new mechanisms (or combinations of mechanisms) of action, 3) improved pharmacokinetic properties. This article will discuss the next generation of anticonvulsants (carabersat, CGX-1007, fluorofelbamate, harkoseride, losigamone, pregabalin, retigabine, safinamide, SPD-421, talampanel, valrocemide) and the possible populations in which they would be clinically useful.

Effect of low-affinity NMDA receptor antagonists on electrical activity in mouse cortical slices

The objective of this study was to investigate the effects of three low-affinity NMDA receptor antagonists, MRZ 2/279 (1-amino-1,3,3,5,5-pentamethyl-cyclohexane HCl), AR-R 15896AR ([+]-alpha-phenyl-2-pyridine-ethanamine diHCl) and dextromethorphan on epileptiform activity in vitro. Epileptiform discharges were elicited in DBA/2 mouse cortical slices by perfusion with Mg(2+)-free artificial cerebrospinal fluid. MRZ 2/279, AR-R 15896AR and dextromethorphan all reversibly decreased the frequency of the discharges in a concentration-dependent manner. The IC(50)'s for MRZ 2/279, AR-R 15896AR and dextromethorphan were 5.2, 10.8 and 55.9 microM, respectively. These low-affinity NMDA receptor antagonists may be proved to be clinically effective with fewer adverse effects than drugs with high-affinity for the NMDA receptor-operated channel.

Hypoxia/hypoglycemia-induced amino acid release is decreased in vitro by preconditioning

The aim of this study was to investigate the effects of preconditioning on amino acid neurotransmitter release, induced by hypoxia/hypoglycaemia, from rat brain cortical slices. Tissue, perfused with artificial cerebrospinal fluid (aCSF) at 37 degrees C with zero glucose and gassed with 95% nitrogen and 5% carbon dioxide, showed a fivefold increase in glutamate release with little effect on gamma-aminobutyric acid (GABA) release. Preconditioning, with three 5-min periods of hypoxia/hypoglycaemia preceding continuous hypoxia/hypoglycaemia, significantly decreased glutamate release whilst significantly elevating GABA release. These results suggest that GABA may reduce the release of glutamate and consequently decrease the neurotoxic effects of glutamate.

An assessment of zonisamide as an anti-epileptic drug

A brief review of epilepsy as a disease, anti-epileptic drugs and methods of evaluation of anti-epileptic drugs are presented as a background for assessment of zonisamide, which has been approved by the FDA as add-on therapy for the treatment of partial seizures with or without secondary generalisation in adults. Chemically, zonisamide is classified as a sulphonamide and is unrelated to other anti-epileptic drugs. The mode of action of zonisamide remains unclear, but likely mechanisms are blockade of sodium and T-type calcium channels. It is also shown to have some neuroprotective effect against hypoxia and ischaemia. It has a liner pharmacokinetics with excellent oral bioavailability. Zonisamide has been approved for use in Japan for ten years prior to approval in USA and Europe. Clinical experience with zonisamide in Japan has documented its efficacy in the treatment of partial seizures (partial-onset generalised tonic-clonic, simple partial and/or complex partial seizures) and to a more variable extent, generalised tonic-clonic, generalised tonic (mainly seen in symptomatic generalised epilepsies including Lennox-Gastaut Syndrome) and compound/combination seizures. The efficacy and safety was confirmed in trials conducted in USA and Europe in adults as well as children. Zonisamide compares favourably with other newly introduced drugs and has the potential for development as a monotherapy for epilepsy.

An assessment of levetiracetam as an anti-epileptic drug

A brief review of epilepsy as a disease, anti-epileptic drugs (AEDs) and methods of evaluation of AEDs are presented as a background for the assessment of levetiracetam which has been approved by the FDA as add-on therapy for the treatment of partial seizures with or without secondary generalisation in adults. The exact mechanism of action of levetiracetam is not known but its action differs from that of other anti-epileptic drugs. A specific binding site for levetiracetam has been identified and is possibly related to anticonvulsant activity. Levetiracetam offers an effective and broad spectrum treatment of epileptic seizures, partial as well as generalised epilepsy. Levetiracetam has been shown to be effective in genetic and kindled animal models of epilepsy and against chemoconvulsant-induced partial epileptic seizures. Levetiracetam has a near perfect pharmacokinetic profile, with rapid absorption following oral administration, excellent bioavailability, quick attainment of steady-state concentrations, linear kinetics and minimal plasma protein binding. Levetiracetam does not interact with commonly used drugs and other AEDs. In recent Phase III clinical trials, the responder rate was 39.4 - 42.1% on 3000 mg dose, compared with placebo rates of 10.9 - 16.7%. Levetiracetam has a favourable safety profile and the most frequently reported adverse events were somnolence, asthenia and dizziness. Overall, levetiracetam is considered to have several advantages over current AEDs.

An assessment of rufinamide as an anti-epileptic in comparison with other drugs in clinical development

This article evaluates rufinamide, a new anti-epileptic drug (AED) in Phase III development. This review is done against the background of therapeutic challenges of epilepsy, old established AEDs, newly introduced AEDs and AEDs in clinical development. Pharmacological properties of 12 AEDs in clinical trials (Phases I - III) are compared: ADCI, AWD 131-138, DP-VPA, ganaxolone, levetiracetam, losigamone, pregabalin, remacemide hydrochloride, retigabine, rufinamide, soretolide and TV1901. One of these, levetiracetam has been approved in the USA and is waiting approval in other countries. The protective index of rufinamide, as shown in rodent models of epilepsy, is much higher than that of most common AEDs. Features which make it a desirable AED are: (i) a broad spectrum of anti-epileptic actions including both partial and symptomatic generalised epilepsy; (ii) a statistically significant reduction in seizure frequency in clinical trials; (iii) efficacy and safety shown in a broad range of age groups including children and the elderly; (iv) rapid oral absorption enabling quick titration to effective dose and (v) a benign adverse event profile. Most of the events did not lead to discontinuation in clinical trials. These features offer considerable advantages over the existing anti-epileptic drugs. It is one of the two drugs in development which have reached Phase III and is expected to be approved by the year 2001 - 2002.