Influence of sex hormone antagonists on the anticonvulsant action of conventional antiepileptic drugs against amygdala-kindled seizures in male and female rats.

The effects of three gonadal steroid antihormones, tamoxifen (TXF, an estrogen antagonist), cyproterone acetate (CYP, an antiandrogen) and mifepristone (MIF, a progesterone antagonist) alone or combined with conventional antiepileptics were evaluated in amygdala-kindled seizures in male and female rats. None of the three antihormones used in this study affected any seizure parameter. TXF (50 mg/kg) and CYP (50 mg/kg), when combined with carbamazepine, or phenobarbital applied at their subprotective doses of 15 mg/kg, resulted in significant reductions of the seizure and afterdischarge durations, both in male and female rats. Additionally, the combination of carbamazepine and CYP markedly increased the afterdischarge threshold in fully-kindled rats of both genders. The interaction between antihormones and carbamazepine, or phenobarbital, was not reversed by respective sex steroid hormones (estradiol, testosterone). However, the TXF- and CYP-induced anticonvulsant effects in combinations with carbamazepine were attenuated by bicuculline, N-methyl-D-aspartate (NMDA) and aminophylline. Kainic acid and strychnine remained ineffective in this respect. The effect of a combination of TXF with phenobarbital was reversed by bicuculline and NMDA and that of CYP with phenobarbital-by bicuculline and aminophylline. Neither TXF nor CYP altered the free plasma concentrations of carbamazepine or phenobarbital, so a pharmacokinetic interaction is not probable. The combined treatment of the two antihormones with antiepileptic drugs did not affect motor performance, and did not result in significant long-term memory deficits. Our data confirm the hypothesis that sex hormone antagonist-mediated events may play some role in seizure processes in the central nervous system and can modulate the protective activity of some conventional antiepileptic drugs against kindled seizures.     

2-Methyl-6-phenylethynyl-pyridine (MPEP), a non-competitive mGluR5 antagonist,differentially affects the anticonvulsant activity of four conventional antiepileptic drugs against amygdala-kindled seizures in rats

2-Methyl-6-phenylethynyl-pyridine (MPEP), a selective noncompetitive mGluR5 antagonist, influences the action of conventional antiepileptic drugs in amygdala-kindled seizures in rats. MPEP alone (up to 40 mg/kg) did not affect any seizure parameter. Moreover, the common treatment of MPEP with either carbamazepine or phenytoin (administered at subeffective doses) did not result in any anticonvulsant action in kindled rats. However, when combined with subprotective doses of valproate or phenobarbital, MPEP significantly shortened seizure and afterdischarge durations. Importantly, combinations of MPEP with the two antiepileptics did not have the adverse effects of impaired motor performance or long-term memory in rats. Our data indicate that MPEPmay positively interact with some conventional antiepileptic drugs in the amygdala-kindling model of complex partial seizures.     

Effect of amlodipine upon the protective activity of antiepileptic drugs against maximal electroshock-induced seizures in mice.

Amlodipine, a calcium channel antagonist of the dihydropyridine class, up to 10 mg kg(-1)(i.p.) did not significantly affect the threshold for electroconvulsions. However, this calcium channel antagonist (10 mg kg(-1)) enhanced the anticonvulsive activity of carbamazepine, valproate and phenobarbital against maximal electroshock-induced seizures in mice. Furthermore, amlodipine (5 mg kg(-1)) intensified the protection offered by carbamazepine. This effect was associated with the increased free plasma level of carbamazepine in the presence of amlodipine. Amlodipine did not influence the free or total plasma level of phenobarbital and valproate, so a pharmacokinetic interaction is not probable for valproate and phenobarbital. The anticonvulsive action and free plasma level of diphenylhydantoin was not modified by amlodipine. The combined treatment of the calcium channel antagonist and antiepileptics caused motor impairment (evaluated in the chimney test). Long-term memory (assessed in the passive avoidance test) in case of combinations of amlodipine with carbamazepine or diphenylhydantoin was not affected. The combination of amlodipine with valproate or phenobarbital significantly influenced the retention in this test. A possible usefulness of amlodipine as add-on therapy in epileptic patients may be limited by its considerable adverse effect revealed by behavioural tests. The pharmacokinetic interaction between carbamazepine and amlodipine might have some clinical importance for patients treated with these drugs.     

Glutamate receptor antagonists differentially affect the protective activity of conventional antiepileptics against amygdala-kindled seizures in rats.

LY 300164 (5 mg/kg), a selective non-competitive antagonist of AMPA/kainate receptors, exerted a significant anticonvulsant effect in amygdala-kindled rats, being ineffective at 2 mg/kg. LY 235959 (1--5 mg/kg), a selective competitive antagonist of NMDA receptors, failed to modify behavioral and electrographic correlates of kindled seizures. Amygdala-kindled seizures were inhibited by conventional antiepileptics, their lowest effective doses were: 20 mg/kg for carbamazepine and phenobarbital, 50 mg/kg for diphenylhydantoin, and 100 mg/kg for valproate magnesium. The combined treatment of the AMPA/kainate antagonist (2 mg/kg) with valproate at sub-effective doses (25--75 mg/kg) resulted in the reduced severity and duration of kindled seizures. Also, a clear-cut protective effect was observed when LY 235959 was co-administered with diphenylhydantoin (40 mg/kg). Any interaction at the pharmacokinetic level can be excluded because neither LY 300164 nor LY 235959 interfered with the free plasma levels of valproate or diphenylhydantoin, respectively. The combination of the AMPA/kainate receptor antagonist (2 mg/kg) with valproate (75 mg/kg) did not impair performance of rats in the rotorod test (motor co-ordination) or passive-avoidance task (long-term memory). Conversely, the NMDA receptor antagonist alone or in combination with diphenylhydantoin, produced significant mnemonic deficits. The results indicate that AMPA/kainate receptor antagonists might be of importance as adjuvant antiepileptic drugs in patients treated with valproate. A possible use of NMDA receptor antagonists may be questionable.     

Effect of felbamate and its combinations with conventional antiepileptics in amygdala-kindled rats

We investigated the effect of felbamate, administered singly and in combination with carbamazepine, phenobarbital, phenytoin or clonazepam, on various behavioral and electrographic correlates of seizures in amygdala-kindled rats. Felbamate (5 or 10 mg/kg) significantly increased afterdischarge threshold, shortened seizure and afterdischarge durations but remained without effect on seizure severity. Furthermore, the combination of felbamate (2.5 mg/kg) with carbamazepine (7.5 mg/kg; both drugs at their subeffective doses), was associated with the reduction in seizure severity and afterdischarge duration. In relation to the afterdischarge duration, the antiseizure potency of felbamate and carbamazepine, in combination, was comparable with that of carbamazepine (10 mg/kg) administered alone. Neither carbamazepine (7.5 and 10 mg/kg) nor felbamate (2.5-10 mg/kg) affected seizure severity, whereas the combined administration of felbamate (2.5 mg/kg) with carbamazepine (7.5 mg/kg) led to significant reduction in seizure severity from the fifth to the third stage of Racine's scale. Among the conventional antiepileptic drugs evaluated in this study, only valproate (100 mg/kg) and clonazepam (0.1 mg/kg) exerted similar action on seizure severity. However, the combinations of felbamate (2.5 mg/kg), with subeffective doses of valproate, phenobarbital, phenytoin or clonazepam, were not associated with any protective action. As blood and brain felbamate and carbamazepine concentrations were unaffected, a pharmacokinetic interaction can be excluded and a pharmacodynamic interaction concluded. These data suggest that felbamate and carbamazepine, administered in combination, may be useful in patients with drug-resistant partial epilepsy.     

Influence of flunarizine, nicardipine and nimodipine on the anticonvulsant activity of different antiepileptic drugs in mice.

Only flunarizine (40 mg/kg, i.p.) significantly raised the threshold for electroconvulsions in mice (ear-clip electrodes, 0.2 sec stimulus duration, tonic hindlimb extension as an endpoint), whilst nicardipine and nimodipine (up to 80 mg/kg) was ineffective in this respect. Further, flunarizine (10 and 20 mg/kg) potentiated the efficacy of carbamazepine and valproate against maximum electroshock (50 mA)-induced seizures and, in the dose of 20 mg/kg, enhanced that of diphenylhydantoin. In addition, this calcium channel inhibitor was without influence upon the total levels of these antiepileptics in plasma. Nicardipine (5 and 10 mg/kg) and nimodipine (10 and 20 mg/kg) increased the protective potential of carbamazepine and nimodipine (20 mg/kg) also decreased the ED50 of diphenylhydantoin against maximum electroshock. However, nicardipine distinctly increased the level of carbamazepine in plasma, whilst nimodipine did not affect the level of both antiepileptics in plasma. The combined treatment of calcium channel inhibitors and antiepileptic drugs, providing a 50% protection against maximum electroshock, did not significantly change the motor performance of mice in the chimney test, when compared with antiepileptic drugs, given alone at their ED50s, against maximum electroshock-induced convulsions. The present results give further support to the idea of the combined use of some calcium channel inhibitors and antiepileptic drugs in the treatment of human epilepsy.     

Influence of antazoline and ketotifen on the anticonvulsant activity of conventional antiepileptics against maximal electroshock in mice.

Experimental studies have indicated that the central histaminergic system plays an important role in the inhibition of seizures through the stimulation of histamine H1 receptors. H1 receptor antagonists, including classical antiallergic drugs, occasionally may induce convulsions in healthy children and patients with epilepsy. The purpose of this study was to investigate the effects of antazoline and ketotifen (two H1 receptor antagonists) on the anticonvulsant activity of antiepileptic drugs against maximal electroshock (MES)-induced convulsions in mice. The following antiepileptic drugs were used: valproate, carbamazepine, diphenylhydantoin and phenobarbital. In addition, the effects of antiepileptic drugs alone or in combination with antazoline or ketotifen were studied on long-term memory (tested in the passive avoidance task) and motor performance (evaluated in the chimney test), acutely and after 7-day treatment with these H1 receptor antagonists. The influence of antazoline and ketotifen on the free plasma and brain levels of the antiepileptics was also evaluated. Antazoline (at 0.5 mg/kg), given acutely and after 7-day treatment, significantly diminished the electroconvulsive threshold. Similarly, ketotifen, after acute and chronic doses of 8 mg/kg markedly reduced the threshold for electroconvulsions. In both cases, antazoline and ketotifen were without effect upon this parameter at lower doses. Antazoline (0.25 mg/kg) significantly raised the ED50 value of carbamazepine against MES (both, acutely and after 7-day treatment). Furthermore antazoline (0.25 mg/kg) also reduced the anticonvulsant activity of diphenylhydantoin, but only after repeated administration, without modifying the brain and free plasma level of this drug. Moreover, valproate and phenobarbital did not change their protective activity when combined with antazoline. Ketotifen (4 mg/kg) possessed a biphasic action, acutely it enhanced the anticonvulsant action of carbamazepine and phenobarbital while, following 7-day treatment, reduced the antiseizure activity of carbamazepine. Ketotifen did not affect the free plasma or brain levels of antiepileptics tested. Only acute antazoline (0.25 mg/kg) applied with valproate impaired the performance of mice evaluated in the chimney test. Ketotifen (4 mg/kg) co-administered with conventional antiepileptic drugs impaired motor coordination in mice treated with valproate, phenobarbital or diphenylhydantoin. Acute and chronic antazoline (0.25 mg/kg) alone or in combination with antiepileptic drugs did not disturb long-term memory, tested in the passive avoidance task. Similarly, ketotifen (4 mg/kg) did not impair long-term memory, acutely and after 7-day treatment. However, valproate alone or in combination with chronic ketotifen (4 mg/kg) worsened long-term memory. The results of this study indicate that H1 receptor antagonists, crossing the blood brain barrier, should be used with caution in epileptic patients. This is because antazoline reduced the protective potential of diphenylhydantoin and carbamazepine. Also, ketotifen reduced the protection offered by carbamazepine and elevated the adverse activity of diphenylhydantoin, phenobarbital and valproate.     

Influence of the antagonist of the glycine site of NMDA receptors, MRZ 2/576, on the anticonvulsant activity of conventional antiepileptic drugs in mice

The purpose of this study was to evaluate the influence of the glycine site antagonist of the NMDA receptor, MRZ 2/576 (8-chloro-4-hydroxy-1-oxo-1,2-dihydropyridazino[4,5-b]quinolin-5-oxide choline salt), on the anticonvulsive activity of carbamazepine, oxcarbazepine, diphenylhydantoin, phenobarbital and valproate against maximal electroshock (MES)-induced seizures and ethosuximide, valproate and clonazepam against pentetrazole (PTZ)-induced seizures in mice. MRZ 2/576 applied intraperitoneally 5 min before electroconvulsions, at the dose of 10 and 15 mg/kg, significantly raised the convulsive threshold (from 6.9 to 8.8 and 10.8 mA respectively). At lower doses, it did not affect the threshold. MRZ 2/576 applied at the dose of 5, 10 and 20 mg/kg did not influence the clonic phase of PTZ-induced seizures, but protected the animals against the tonic phase. The anticonvulsant effect of a given antiepileptic drug was expressed as its ED(50) value (in mg/kg), which represents the dose of the drug required to protect 50% of animals against MES or PTZ seizures. MRZ2/576 co-administered at a subprotective dose (5 mg/kg) with carbamazepine, oxcarbazepine, diphenylhydantoin, phenobarbital or valproate, significantly reduced their ED(50) values in MES test. Also, at the dose of 2.5 mg/kg it enhanced the protective activity of carbamazepine and valproate. At the lowest tested dose (1.25 mg/kg), it still potentiated the anticonvulsant activity of valproate. However, MRZ 2/576 (5 mg/kg) applied with valproate, ethosuximide or clonazepam did not influence their protective effects in the PTZ test. The combinations of MRZ 2/576 with almost every studied antiepileptic drug (providing a 50% protection against maximal electroshock or PTZ-induced seizures) did not produce motor impairment in the chimney test nor long-term memory deficit measured in the passive avoidance task. Only valproate alone or combined with MRZ 2/576 impaired both of these measures. It may be concluded that MRZ 2/576 enhanced the anticonvulsive activity of antiepileptic drugs against MES without accompanying potentiation of adverse effects. However, there was no positive interaction in the PTZ test. Finally, pharmacokinetic interactions do not seem responsible for the obtained results because MRZ 2/576 (5 mg/kg) did not alter the free plasma levels of the antiepileptics tested in the present study.     

Interaction of loreclezole with conventional antiepileptic drugs in amygdala-kindled rats.

Loreclezole (5 mg/kg) exerted a significant protective action against amygdala-kindled rats, reducing both seizure and afterdischarge (AD) durations. Subsequently, the effect of combinations of loreclezole (at non-effective doses) with some conventional antiepileptics (at their subtherapeutic doses) was evaluated. The co-administration of loreclezole (2.5 mg/kg) with phenobarbital (15 mg/kg) or diphenylhydantoin (2.5 mg/kg) did not influence any seizure correlates. However, the combined treatment of loreclezole (2.5 mg/kg) with valproate (50 mg/kg) significantly reduced the afterdischarge duration. Its combination with carbamazepine (15 mg/kg) reduced the seizure severity (SSv) and both seizure and afterdischarge durations. Also, the concomitant treatment of loreclezole (2.5 mg/kg) with clonazepam (0.05 mg/kg) resulted in a significant decrease of seizure and afterdischarge durations. Loreclezole did not affect the free plasma concentrations of valproate or clonazepam, so a pharmacokinetic interaction is not probable. Although, loreclezole significantly increased the free plasma concentration of carbamazepine. The results point to the potential therapeutic effects of combinations of loreclezole with valproate or clonazepam.     

Influence of chronic treatment with H1 receptor antagonists on the anticonvulsant activity of antiepileptic drugs.

The aim of this study was to evaluate the effects of chronic astemizole and ketotifen administration on the anticonvulsant activity of antiepileptic drugs against maximal electroshock-induced convulsions in mice. Adverse effects were evaluated in the chimney test (motor performance) and passive avoidance task (long-term memory). Brain and plasma levels of antiepileptics were measured by immunofluorescence. Astemizole (2 mg/kg) and ketotifen (8 mg/kg) significantly diminished the electroconvulsive threshold, being without effect upon this parameter at lower doses. Astemizole significantly reduced the anticonvulsant action of phenobarbital and diphenylhydantoin, but it did not affect that of carbamazepine and valproate. Moreover, ketotifen (at the subprotective dose of 4 mg/kg) remained without effect upon the protective activity of valproate, diphenylhydantoin or phenobarbital, but significantly diminished the anticonvulsant effect of carbamazepine. Histamine receptor antagonists combined with antiepileptic drugs, did not alter their brain and free plasma levels. Also, they did not influence adverse potential of carbamazepine, diphenylhydantoin and valproate while that of phenobarbital was significantly enhanced. Valproate, phenobarbital and diphenylhydantoin alone at their ED50s against maximal electroshock or combined with the histamine receptor antagonists disturbed long-term memory. The results of this study indicate that H1 receptor antagonists, should be used with caution in epileptic patients.     

2-Chloroadenosine, a preferential agonist of adenosine A1 receptors, enhances the anticonvulsant activity of carbamazepine and clonazepam in mice.

2-Chloroadenosine (0.25-1 mg/kg) significantly raised the threshold for electroconvulsions in mice. This preferential adenosine A(1) receptor agonist (at 0.125 mg/kg) significantly potentiated the protective activity of carbamazepine against maximal electroshock-induced seizures in mice. 2-Chloroadenosine (1 mg/kg) showed also anticonvulsive efficacy against pentylenetetrazol-evoked seizures, raising the CD(50) value for pentylenetetrazol from 77.2 to 93.7 mg/kg. The drug (at 0.5 mg/kg) significantly enhanced the protective action of clonazepam in this test, decreasing its ED(50) value from 0.033 to 0.011 mg/kg. Moreover, aminophylline, a non-selective adenosine receptor antagonist (5 mg/kg), and 8-cyclopentyl-1,3-dimethylxanthine (8-CPX), a selective A(1) adenosine receptor antagonist (5 mg/kg) reversed the 2-chloroadenosine (0.125 mg/kg)-induced enhancement of the protective activity of carbamazepine and clonazepam. 2-Chloroadenosine administered alone or combined with antiepileptic drugs, caused neither motor nor long-term memory impairment. Finally, the adenosine A(1) agonist did not change the free plasma concentration of antiepileptics, so a pharmacokinetic factor is not probable. Summing up, 2-chloroadenosine potentiated the protective activity of both carbamazepine and clonazepam, which seems to be associated with the enhancement of purinergic transmission mediated through adenosine A(1) receptors.     

Effect of antihormones in amygdala-kindled seizures in rats.

Tamoxifen (TXF; an antiestrogen), cyproterone acetate (CYP; an antiandrogen) and mifepristone (MIF; an antigestagen) did not affect kindling parameters (afterdischarge threshold, seizure severity, seizure duration and afterdischarge duration) in fully-kindled rats. TXF (50 mg/kg) and CYP (50 mg/kg), when combined with carbamazepine, or phenobarbital, both antiepileptics administered at their highest subprotective doses of 15 mg/kg, resulted in significant reduction of the seizure and afterdischarge durations, both in male and female rats. Additionally, the combination of carbamazepine and cyproterone markedly increased the afterdischarge threshold in fully-kindled rats of both genders. The interaction between antihormones and carbamazepine, or phenobarbital, was not reversed by the respective gonadal hormones (estradiol, progesterone, and testosterone), kainic acid, or strychnine. However, the TXF-, and CYP-induced effect on the action of carbamazepine was abolished by bicuculline, N-methyl-D-aspartic acid and aminophylline. The effect of TXF on the protective activity of phenobarbital was reversed by bicuculline and N-methyl-D-aspartic acid. Finally, the CYP-mediated effect on phenobarbital action was abolished by bicuculline and aminophylline. Neither TXF nor CYP altered free plasma levels and brain levels of carbamazepine or phenobarbital, so a pharmacokinetic interaction between antihormones and antiepileptic drugs is not probable. In view of the present data, it may be suggested that the protective activity of the antiestrogen and antiandrogen are mostly associated with the enhancement of GABA-ergic and purinergic transmission in the central nervous system. Also the augmentation of glutamatergic transmission, realized through NMDA receptors, may be involved in the mechanism of antiseizure action of TXF and CYP.     

N(6)-2-(4-aminophenyl)ethyl-adenosine enhances the anticonvulsive action of conventional antiepileptic drugs in the kindling model of epilepsy in rats.

APNEA [(N(6)-2-(4-aminophenyl)ethyl-adenosine; a non-selective adenosine A(3) receptor agonist; 2-4 mgkg(-1)] had no significant effect on seizure parameters (seizure severity, seizure duration and afterdischarge duration) in amygdala-kindled rats. Subsequently, APNEA was combined with antiepileptic drugs administered at doses ineffective in fully kindled rats. Co-administration of APNEA (0.5-2 mg kg(-1)) with carbamazepine (2.5-20 mg kg(-1)) resulted in the significant reduction of all studied seizure parameters. Moreover, 8-cyclopentyl-1,3-dimethylxanthine 8-CPX (a selective adenosine A(1) receptor antagonist; 5 mg kg(-1)) partially reduced the anticonvulsive activity of a combination of APNEA (2 mg kg(-1)) with carbamazepine (20 mg kg(-1)), but not that of carbamazepine (20 mgkg(-1))+APNEA (0.5 mg kg(-1)). When APNEA (2 mg kg(-1)) was combined with phenobarbital (20 mg kg(-1)), valproate (75 mg kg(-1)) or clonazepam (0.003 mg kg(-1)), seizure and afterdischarge durations were significantly shortened. 8-CPX (5 mg kg(-1)) totally reversed the APNEA (2 mg kg(-1))-induced enhancement of the anticonvulsive action of valproate. However, when the non-selective adenosine A(3) receptor agonist was administered together with diphenylhydantoin, no protection was observed in the kindling model of epilepsy. The interaction at the pharmacokinetic level can be excluded because APNEA did not interfere with the free plasma level of antiepileptics used in this study. It may be concluded that the interaction of APNEA with carbamazepine involves A(3) adenosine receptor-dependent events.     

Influence of sexual hormone antagonists on the anticonvulsant action of conventional antiepileptic drugs against electrically- and pentylenetetrazol-induced seizures in mice.

The present results refer to the action of three gonadal steroid antihormones, tamoxifen (TXF, an estrogen antagonist), cyproterone acetate (CYP, an antiandrogen) and mifepristone (MIF, a progesterone antagonist) on seizure phenomena in mice. TXF and CYP at their lowest protective dose in the electroconvulsive threshold test, enhanced the antiseizure efficacy of some antiepileptic drugs. TXF (20 mg/kg) potentiated the protective activity of valproate, diphenylhydantoin and clonazepam, but not that of carbamazepine or phenobarbital, against maximal electroshock-induced convulsions in female mice. CYP (40 mg/kg) enhanced the anticonvulsant action of valproate, carbamazepine, diphenylhydantoin and clonazepam, but not that of phenobarbital, against maximal electroshock in male animals. MIF failed to affect the electroconvulsive threshold or the efficacy of antiepileptic drugs in maximal electroshock. The effect of TXF or CYP upon the electroconvulsive threshold and on the action of antiepileptics was not reversed by sex steroid hormones (estradiol, testosterone, progesterone). However, the TXF-induced elevation of the electroconvulsive threshold was abolished by bicuculline, N-methyl-D-aspartic acid and kainic acid, and partially reversed by aminophylline, strychnine being ineffective in this respect. The action of CYP on the threshold for electroconvulsions was partially reversed by bicuculline and aminophylline. Both glutamatergic agonists and strychnine remained ineffective in this respect. Moreover, the action of TXF or CYP on the activity of antiepileptics was not influenced by strychnine, and reversed to various extents by the remaining convulsants. In contrast to maximal electroshock, none of the three antihormones affected the protective action of antiepileptic drugs against pentylenetetrazol-induced seizures in mice. Neither TXF nor CYP altered the free plasma levels of antiepileptic drugs, so a pharmacokinetic interaction is not probable. The combined treatment of the two antihormones with antiepileptic drugs, providing 50% protection against maximal electroshock, did not affect motor performance in mice, and did not result in significant long-term memory deficits. Our data indicate that steroid receptor-mediated events may be indirectly associated with seizure phenomena in the central nervous system and can modulate the protective activity of some conventional antiepileptic drugs.     

Influence of agents affecting voltage-dependent calcium channels and dantrolene on the anticonvulsant action of the AMPA/kainate receptor antagonist LY 300164 in mice.

It was previously documented that calcium (Ca(2+)) channel inhibitors intensified the protective effects of conventional antiepileptics against electroconvulsions in mice. The aim of this study was to evaluate the effects of Ca(2+) channel inhibitors (nifedipine, nicardipine and flunarizine) on the anticonvulsant action of the new AMPA/kainate receptor antagonist, 7-acetyl-3-(4-aminophenyl)-8,9-dihydro-8-methyl-7H-1,3-dioxazolo[4,5-h][2,3]-benzodiazepine (LY 300164), against maximal electroshock (MES)-induced seizures in mice. Dantrolene (an inhibitor of Ca(2+)release from intracellular stores) was also included. Nifedipine (30 mg/kg) and flunarizine (15 mg/kg) raised the threshold for electroconvulsions, being ineffective at lower doses. Nicardipine (up to 30 mg/kg) and dantrolene (up to 20 mg/kg) did not affect this parameter. Flunarizine (10 mg/kg), nicardipine (20 mg/kg) and dantrolene (20 mg/kg) potentiated the efficacy of LY 300164 against MES. However, nicardipine (at 20 mg/kg) raised the free plasma concentration of LY 300164. Nifedipine (30 mg/kg), given even in a dose raising the electroconvulsive threshold, did not significantly alter the protective effect of LY 300164 against MES. Furthermore, the Ca(2+) channel agonist-BAY k-8644 (at 5 mg/kg) did not influence the protection offered by LY 300164 against MES. Finally, this Ca(2+) channel activator did not affect the enhanced efficacy of LY 300164 by Ca(2+) channel modulators. The only exception was the combination of LY 300164 with flunarizine. Combined treatment with LY 300164 and dantrolene (20 mg/kg), compared to LY 300164 alone, resulted in an impairment of motor performance in mice. Ca(2+) channel inhibitors were without effect upon this parameter evaluated in the chimney test. As shown in the passive avoidance task, LY 300164 alone (at its ED(50)) or combined with agents affecting neuronal Ca(2+) concentration did not disturb long-term memory. The present results suggest that agents preventing influx of Ca(2+) ions into neurons may enhance the protective action of LY 300164.     

Effects of etomidate,ketamine or propofol,and their combinations with conventional antiepileptic drugs on amygdala-kindled convulsions in rats

Ketamine, etomidate and propofol modified behavioral and electrographic correlates of kindled seizures in rats. In detail, ketamine (5 mg/kg) and propofol (15 mg/kg) significantly increased afterdischarge threshold, reduced seizure severity and shortened seizure and afterdischarge durations. Etomidate (7.5 mg/kg) was effective in terms of seizure and afterdischarge durations. Moreover, the combinations of ketamine (2.5 mg/kg) with carbamazepine (15 mg/kg) or valproate (50 mg/kg; all drugs at their subeffective doses), reduced the severity and duration of kindled seizures. The antiseizure potency of the ketamine/carbamazepine combination was comparable to that of carbamazepine alone administered at 20 mg/kg, while the effect of ketamine/valproate was comparable to the efficacy of valproate alone at 100 mg/kg. However, the combinations of ketamine with phenobarbital or diphenylhydantoin did not exert any protective action. Propofol and etomidate entirely failed to interact with conventional antiepileptics. The combinations of ketamine with carbamazepine or valproate did not induce any significant motor impairment in the chimney test or memory deficit in the passive avoidance task. A pharmacokinetic interaction, at least in plasma, can be excluded, because ketamine (2.5 mg/kg) did not affect the free plasma concentrations of carbamazepine or valproate. Results of the present study may suggest that there may be no risk of negative interactions between injectable anesthetics and antiepileptics in cases of partial epilepsy.     

Interactions of tiagabine with some antiepileptics in the maximal electroshock in mice

Tiagabine (TGB), a new potent gamma-aminobutyric acid (GABA) uptake inhibitor, is widely applied in adjunctive treatment of partial seizures in humans. Although, polytherapy is not an initial method of epilepsy treatment, clinicians often combine TGB with other antiepileptics as add-on therapy for assuring the anticonvulsant protection in patients with refractory seizures. To evaluate the character of pharmacological interactions between TGB and some antiepileptics, the isobolographic analysis was used as a suitable method for determining the exact types of interactions. Determination of an influence of TGB on the protective effects of diphenylhydantoin (DPH), carbamazepine (CBZ), valproate (VPA), phenobarbital (PB), lamotrigine (LTG), topiramate (TPM), and felbamate (FBM) in maximal electroshock-induced seizures was essential for this study. To exclude or confirm a pharmacokinetic character of observed interactions, the free plasma and brain concentrations of antiepileptic drugs (AEDs) studied were evaluated by using the immunofluorescence or high-pressure liquid chromatography (HPLC).TGB (up to 2.5 mg/kg) remained ineffective upon the electroconvulsive threshold, whilst the drug in doses of 5 and 10 mg/kg significantly raised the electroconvulsive threshold in mice. According to the isobolography, TGB appears to act synergistically with VPA. The remaining combinations tested exerted additive interactions. A pharmacokinetic character of interaction between TGB and VPA was evidently corroborated either in plasma or brains. Moreover, TGB significantly reduced the plasma and brain concentrations of DPH; however, pharmacokinetic events were not accompanied by any changes in anticonvulsant activity of the latter. Finally, the isobolographic analysis revealed that combinations of TGB with VPA exerted synergistic (supra-additive) interaction resulting from a pharmacokinetic interaction.     

Interactions between ACE inhibitors and classical antiepileptic drugs in the mouse maximal electroshock seizures

This study evaluated the effect of two angiotensin-converting enzyme (ACE) inhibitors, enalapril and cilazapril, commonly used antihypertensive drugs, on the protective efficacy of the classical antiepileptics — carbamazepine (CBZ), phenytoin (PHT), valproate (VPA) and phenobarbital (PB). For this purpose, we used the maximal electroshock seizure (MES) test in mice. Additionally, adverse effects of combined treatment with ACE inhibitors and antiepileptic drugs in the passive avoidance task and chimney test were assessed. All drugs were administered intraperitoneally. Neither enalapril (10, 20 and 30 mg/kg) nor cilazapril (5, 10 and 20 mg/kg) affected the threshold for electroconvulsions. Enalapril (30 mg/kg) but not cilazapril (20 mg/kg), enhanced the protective action of VPA, decreasing its ED₅₀ value from 249.5 to 164.9 mg/kg (p < 0.01). Free plasma (non-protein-bound) and total brain concentrations of VPA were not significantly influenced by enalapril. Therefore, the observed interaction could be pharmacodynamic in nature. The combinations of ACE inhibitors with other antiepileptics (CBZ, PHT, and PB) were ineffective in that their ED₅₀ values against MES were not significantly changed. Enalapril and cilazapril remained ineffective as regards memory retention in the passive avoidance task or motor performance in the chimney test. The current study suggests that there are no negative interactions between the studied ACE inhibitors and classical antiepileptic drugs. Enalapril was even documented to enhance the anticonvulsant activity of VPA.     

Effect of some convulsants on the protective activity of loreclezole and its combinations with valproate or clonazepam in amygdala-kindled rats

Loreclezole (5 mg/kg) exerted a significant protective action in amygdala-kindled rats, reducing both seizure and afterdischarge durations. The combinations of loreclezole (2.5 mg/kg) with valproate, clonazepam, or carbamazepine (applied at their subprotective doses) also exhibited antiseizure effect in this test. However, only two first combinations occurred to be of pharmacodynamic nature. Among several chemoconvulsants, bicuculline, N-methyl-D-aspartic acid and BAY k-8644 (the opener of L-type calcium channels) reversed the protective activity of loreclezole alone and its combination with valproate. On the other hand, bicuculline, aminophylline and BAY k-8644 inhibited the anticonvulsive action of loreclezole combined with clonazepam. The results support the hypothesis that the protective activity of loreclezole and its combinations with other antiepileptics may involve potentiation of GABAergic neurotransmission and blockade of L-type of calcium channels.     

Influence of calcium channel inhibitors upon the anticonvulsant efficacy of common antiepileptics against pentylenetetrazol-induced convulsions in mice

Among three calcium channel inhibitors studied, nifedipine (20 mg/kg) moderately inhibited pentylenetetrazol (115 mg/kg, s.c.)-induced convulsions, whilst diltiazem (up to 20 mg/kg) and verapamil (up to 20 mg/kg) were without effect. The combinations of nifedipine (10 and 20 mg/kg) with valproate (100 mg/kg) or phenobarbital (6.25 mg/kg) resulted in significant protection against pentylenetetrazol-induced seizures. Combined treatment of nifedipine (5-20 mg/kg) with ethosuximide (100 mg/kg) also provided a clearcut anticonvulsant action. The antiepileptic drugs alone, in the above doses, were ineffective. The combination of diltiazem (10-20 mg/kg) and ethosuximide (100 mg/kg) produced protection against pentylenetetrazol, comparable to that of ethosuximide (200 mg/kg) alone. No pharmacokinetic interactions were found in the case of ethosuximide, whilst nifedipine (10 mg/kg) increased the levels of phenobarbital and valproate in plasma. The combination of diltiazem with the remaining antiepileptics were ineffective. Verapamil (up to 20 mg/kg) was without effect upon the action of the antiepileptic drugs tested. Finally, none of the calcium channel inhibitors studied influenced the action of diazepam (0.2 mg/kg). It may be concluded that combinations of ethosuximide, with either nifedipine or diltiazem, may be promising for the treatment of absence epilepsy.