Synthetic cannabinoid WIN 55,212-2 mesylate enhances the protective action of four classical antiepileptic drugs against maximal electroshock-induced seizures in mice

The aim of this study was to determine the effect of WIN 55,212-2 mesylate (WIN — a non-selective cannabinoid CB1 and CB2 receptor agonist) on the protective action of four classical antiepileptic drugs (carbamazepine, phenytoin, phenobarbital, and valproate) in the mouse maximal electroshock seizure (MES) model. The results indicate that WIN (10 mg/kg, i.p.) significantly enhanced the anticonvulsant action of carbamazepine, phenytoin, phenobarbital and valproate in the MES test in mice. WIN (5 mg/kg) potentiated the anticonvulsant action of carbamazepine and valproate, but not that of phenytoin or phenobarbital in the MES test in mice. However, WIN administered alone and in combination with carbamazepine, phenytoin, phenobarbital and valproate significantly reduced muscular strength in mice in the grip-strength test. In the passive avoidance task, WIN in combination with phenobarbital, phenytoin and valproate significantly impaired long-term memory in mice. In the chimney test, only the combinations of WIN with phenobarbital and valproate significantly impaired motor coordination in mice. In conclusion, WIN enhanced the anticonvulsant action of carbamazepine, phenytoin, phenobarbital and valproate in the MES test. However, the utmost caution is advised when combining WIN with classical antiepileptic drugs due to impairment of motor coordination and long-term memory and/or reduction of skeletal muscular strength that might appear during combined treatment.     

Effect of 4-(4-bromophenyl)-5-(3-chlorophenyl)-2,4-dihydro-3H-1,2,4-triazole-3-thione on the anticonvulsant action of different classical antiepileptic drugs in the mouse maximal electroshock-induced seizure model

The aim of this study was to determine the effects of 4-(4-bromophenyl)-5-(3-chlorophenyl)-2,4-dihydro-3H-1,2,4-triazole-3-thione (TP4-a new S-triazole derivative possessing anticonvulsant properties in preclinical studies) on the protective action of four different classical antiepileptic drugs (carbamazepine, phenobarbital, phenytoin and valproate) against maximal electroshock-induced seizures in mice. Results indicate that TP4 administered intraperitoneally at doses of 75 and 100 mg/kg significantly elevated the threshold for electroconvulsions in mice. TP4 at doses of 12.5, 25, 37.5 and 50 mg/kg had no impact on the threshold for electroconvulsions in mice. Moreover, TP4 (50 mg/kg) significantly enhanced the anticonvulsant activity of carbamazepine, phenobarbital and valproate, but not that of phenytoin in the maximal electroshock seizure test in mice. TP4 at 25 mg/kg significantly potentiated the anticonvulsant action of carbamazepine, but not that of phenobarbital, phenytoin and valproate in the mouse maximal electroshock-induced seizure model. Pharmacokinetic experiments revealed that TP4 significantly elevated total brain concentrations of carbamazepine and valproate, having no impact on total brain concentrations of phenobarbital in mice. In conclusion, the enhanced anticonvulsant action of phenobarbital by TP4 was probably pharmacodynamic in nature and, therefore, the combination of TP4 with phenobarbital is worthy of consideration while extrapolating the results from this study into clinical settings. The enhanced anticonvulsant action of carbamazepine and valproate by TP4 in the mouse maximal electroshock-induced seizure model was associated with pharmacokinetic increases in total brain concentrations of the antiepileptic drugs in mice. The combination of TP4 with phenytoin was neutral from a preclinical point of view.     

Imperatorin enhances the protective activity of conventional antiepileptic drugs against maximal electroshock-induced seizures in mice

The effects of imperatorin (8-isopentenyloxypsoralen; 9-(3-methylbut-2-enyloxy)-7H-furo[3,2-g]chromen-7-one) on the anticonvulsant activity of four conventional antiepileptic drugs (carbamazepine, phenobarbital, phenytoin and valproate) were studied in the mouse maximal electroshock seizure model. Results indicate that imperatorin (30 and 40 mg/kg, i.p.) significantly potentiated the anticonvulsant activity of carbamazepine against maximal electroshock-induced seizures by reducing its median effective dose (ED(50)) from 10.3 to 6.8 (by 34%; P<0.05) and 6.0 mg/kg (by 42%; P<0.01), respectively. Similarly, imperatorin (40 mg/kg, i.p.) markedly enhanced the antielectroshock action of phenobarbital and phenytoin, by lowering their ED(50) values from 19.6 to 12.2 mg/kg (by 38%; P<0.05-phenobarbital) and from 12.8 to 8.5 mg/kg (by 34%; P<0.05-phenytoin) in the maximal electroshock seizure test. In contrast, imperatorin (40 mg/kg, i.p.) did not affect the protective action of valproate against maximal electroshock-induced seizures in mice. Imperatorin at lower doses of 20 and 30 mg/kg had no significant effect on the anticonvulsant activities of conventional antiepileptic drugs in the mouse maximal electroshock seizure model. Pharmacokinetic evaluation of interaction between imperatorin (30 mg/kg, i.p.) and carbamazepine (6.8 mg/kg, i.p.) revealed a significant increase in total brain carbamazepine concentration after imperatorin administration, indicating a pharmacokinetic nature of interaction between these drugs. In cases of phenobarbital and phenytoin, imperatorin (40 mg/kg, i.p.) did not alter significantly total brain concentrations of phenytoin and phenobarbital in mice, and thus, the observed interactions in the maximal electroshock seizure test between imperatorin and phenobarbital or phenytoin were pharmacodynamic in nature. The present study demonstrates that imperatorin enhanced the antiseizure effects of carbamazepine, phenobarbital and phenytoin in the mouse maximal electroshock seizure model. However, the combination of imperatorin with carbamazepine, despite its beneficial effects in terms of seizure suppression in mice, was complicated by a pharmacokinetic increase in total brain carbamazepine concentration in experimental animals. In contrast, the combinations of imperatorin with phenytoin and phenobarbital, due to their beneficial antiseizure effects and no pharmacokinetic interactions between drugs in the brain compartment of experimental animals, deserve more attention and are of pivotal importance for epileptic patients as advantageous combinations from a clinical viewpoint.     

Effect of p-isopropoxyphenylsuccinimide monohydrate on the anticonvulsant action of carbamazepine,phenobarbital, phenytoin and valproate in the mouse maximal electroshock-induced seizure model

This study was designed to determine the effects of p-isopropoxyphenylsuccinimide monohydrate (IPPS) on the protective action of four classical antiepileptic drugs (carbamazepine, phenobarbital, phenytoin and valproate) in the mouse maximal electroshock seizure model.Tonic hind limb extension (seizure activity) was evoked in adult male albino Swiss mice by a current (sine-wave, 25 mA, 500 V, 50 Hz, 0.2 s stimulus duration) delivered via auricular electrodes. Acute adverse-effect profiles with respect to motor performance, long-term memory and skeletal muscular strength were measured along with total brain antiepileptic drug concentrations. Results indicate that IPPS administered intraperitoneally (ip) at doses of 75 and 150 mg/kg significantly elevated the threshold for electroconvulsions in mice. IPPS at lower doses of 18.75 and 37.5 mg/kg had no impact on the threshold for electroconvulsions in mice. Moreover, 37.5 mg/kg IPPS significantly enhanced the anticonvulsant activity of phenytoin and valproate, but not that of carbamazepine or phenobarbital, in the maximal electroshock seizure test in mice. IPPS (18.75 mg/kg) had no impact on the antiseizure action of phenytoin and valproate against maximal electroshock-induced seizures in mice. Pharmacokinetic experiments revealed that IPPS did not alter total brain concentrations of phenytoin or valproate in mice.In conclusion, the enhanced anticonvulsant action of phenytoin and valproate by IPPS in the mouse maximal electroshock-induced seizure model and lack of pharmacokinetic interactions make the combinations of IPPS with phenytoin and valproate of pivotal importance for further experimental and clinical studies. The combinations of IPPS with carbamazepine and phenobarbital are neutral from a preclinical viewpoint.     

Acute and chronic treatment with mianserin differentially affects the anticonvulsant activity of conventional antiepileptic drugs in the mouse maximal electroshock model

Rationale Epilepsy often coexists with depression. Therefore, the probability of simultaneous treatment with antiepileptics and antidepressants and the possibility of interactions between them are relatively high. Objective The effects of acute and chronic administration of mianserin on the protective activity of valproate (VPA), carbamazepine, phenytoin, and phenobarbital were evaluated in the maximal electroshock in mice. Materials and methods Animals were subjected to electroconvulsions. Undesired effects were evaluated in the chimney test (motor impairment) and passive-avoidance task (memory deficit). Brain concentrations of antiepileptic drugs were assessed by immunofluorescence. Results When given acutely, mianserin (at doses greater than or equal to 20 mg/kg) significantly raised the electroconvulsive threshold. The antidepressant, at the subanticonvulsant doses, enhanced the anticonvulsant action of carbamazepine, phenytoin, and VPA. Mianserin administered chronically at 30 mg/kg significantly decreased the electroconvulsive threshold. In contrast to acute treatment, the antidepressant at subeffective doses diminished the anticonvulsant activity of VPA and phenytoin. Mianserin given either acutely or chronically did not affect the brain concentrations of antiepileptic drugs, so a pharmacokinetic contribution to the observed interactions is not probable. Acute and chronic treatment with mianserin and its combinations with antiepileptic drugs did not impair either motor coordination or long-term memory. Conclusion Although acute application of mianserin may potentiate the anticonvulsant action of some antiepileptics, its chronic administration can lead to the opposite effect. Therefore, as far as the presented results can be transferred to clinical conditions, the antidepressant therapy with mianserin should be limited or even avoided in epileptic patients.     

Influence of carbenoxolone on the anticonvulsant efficacy of conventional antiepileptic drugs against audiogenic seizures in DBA/2 mice

Carbenoxolone, the succinyl ester of glycyrrhetinic acid, is an inhibitor of 11beta-hydroxy steroid dehydrogenase and gap junctional intercellular communication. It is currently used in clinical treatment of ulcer diseases. Systemic administration of carbenoxolone (1-40 mg/kg, intraperitoneally (i.p.)) was able to produce a dose-dependent decrease in DBA/2 audiogenic seizure severity score. Glycyrrhizin, an analogue of carbenoxolone inactive at the gap-junction level, was unable to affect audiogenic seizures at doses up to 30 mg/kg. In combination with conventional antiepileptic drugs, carbenoxolone, 0.5 mg/kg, i.p., which per se did not significantly affect the occurrence of audiogenic seizures in DBA/2 mice, potentiated the anticonvulsant activity of carbamazepine, diazepam, felbamate, gabapentin, lamotrigine, phenytoin, phenobarbital and valproate against sound-induced seizures in DBA/2 mice. This effect was not observed after the combination of glycyrrhizin (10 mg/kg, i.p.) with some conventional antiepileptic drugs. The degree of potentiation induced by carbenoxolone was greater for diazepam, felbamate, gabapentin, phenobarbital and valproate, less for lamotrigine, phenytoin and carbamazepine. This increase was associated with a comparable impairment in motor activity; however, the therapeutic index of combined treatment of antiepileptic drugs with carbenoxolone was more favourable than the combination with glycyrrhizin or saline. Since carbenoxolone did not significantly influence the total and free plasma levels of diazepam, felbamate, gabapentin, lamotrigine, phenytoin, phenobarbital, valproate and carbamazepine, pharmacokinetic interactions are not likely. However, the possibility that carbenoxolone can modify the brain clearance of the anticonvulsant drugs studied may not be excluded. In addition, carbenoxolone did not significantly affect the hypothermic effects of the anticonvulsants tested. In conclusion, carbenoxolone showed an additive anticonvulsant effect when administered in combination with some classical anticonvulsants, most notably diazepam, felbamate, gabapentin, phenobarbital, and valproate, implicating a possible therapeutic relevance of such drug combinations.     

Influence of retigabine on the anticonvulsant activity of some antiepileptic drugs against audiogenic seizures in DBA/2 mice

Retigabine (D-2319, 0.5-20 mg/kg i.p.) antagonised dose dependently audiogenic seizures in DBA/2 mice. Retigabine at 0.5 mg/kg i.p., a dose that per se did not affect the occurrence of audiogenic seizures significantly, potentiated the anticonvulsant activity of carbamazepine, diazepam, felbamate, lamotrigine, phenytoin, phenobarbital and valproate against sound-induced seizures in DBA/2 mice. The degree of additivity for the effect induced by retigabine was greatest for diazepam, phenobarbital, phenytoin and valproate, less for carbamazepine and lamotrigine and least for felbamate. The increase in anticonvulsant activity was usually associated with a comparable increase in motor impairment. However, the therapeutic index of combined treatment (drugs plus retigabine), was more favourable than the same drug plus vehicle. Since retigabine had no significant influence on the total and free plasma levels of the anticonvulsant drugs, pharmacokinetic interactions, in terms of total or free plasma levels, are not probable. However, the possibility that retigabine modifies the clearance of the anticonvulsant drugs from the brain cannot be excluded. Retigabine had no significant effect on the hypothermic effects of the anticonvulsants tested. In conclusion, retigabine showed an additive effect when administered in combination with classical anticonvulsants, most notably diazepam, phenobarbital, phenytoin and valproate.     

2-phosphonomethyl-pentanedioic acid (glutamate carboxypeptidase II inhibitor) increases threshold for electroconvulsions and enhances the antiseizure action of valproate against maximal electroshock-induced seizures in mice

This study examined the effect of 2-(phosphonomethyl)-pentanedioic acid (2-PMPA), a potent and selective inhibitor of glutamate carboxypeptidase II (GCP II), an enzyme releasing glutamate and N-acetyl-aspartate from synaptical terminals, on the electroconvulsive threshold in mice. Moreover, the influence of 2-PMPA on the anticonvulsant activities of four conventional antiepileptic drugs (carbamazepine, phenobarbital, phenytoin and valproate) was evaluated in the maximal electroshock-induced seizure test in mice. Results indicated that 2-PMPA (at a dose range of 50-200 mg/kg, i.p.) raised the electroconvulsive threshold in mice dose-dependently. Linear regression analysis of dose-response relationship between the doses of 2-PMPA and their corresponding threshold values allowed the calculation of threshold increasing dose by 20% (TID20), which was 109.2 mg/kg. Moreover, 2-PMPA administered i.p. at a constant dose of 150 mg/kg (the dose increasing the threshold for electroconvulsions) enhanced significantly the anticonvulsant action of valproate, by reducing its median effective dose (ED50) from 281.4 to 230.1 mg/kg (P<0.05). In contrast, 2-PMPA at the lower dose of 100 mg/kg (i.p.) had no impact on the antiseizure activity of valproate in the maximal electroshock-induced seizure test. Likewise, 2-PMPA at 100 and 150 mg/kg did not affect the antiseizure action of carbamazepine, phenobarbital and phenytoin against maximal electroshock-induced seizures in mice. Additionally, none of the combinations investigated between 2-PMPA (150 mg/kg, i.p.) and carbamazepine, phenobarbital, phenytoin and valproate (at their ED50 values) produced motor coordination impairment in the chimney test. Pharmacokinetic evaluation of interaction between 2-PMPA and valproate revealed that 2-PMPA at 150 mg/kg selectively increased total brain concentrations of valproate, remaining simultaneously without any effect on free plasma concentrations of valproate, indicating a pharmacokinetic nature of observed interaction in the maximal electroshock-induced seizures in mice. Based on our preclinical data, it may be concluded that 2-PMPA possesses a seizure modulating property by increasing the electroconvulsive threshold. The reduction of glutamate neurotransmission in the brain, as a consequence of inhibition of GCP II activity by 2-PMPA, was however insufficient to enhance the anticonvulsant activity of conventional antiepileptic drugs, except for valproate, whose antiseizure action against maximal electroconvulsions was potentiated by 2-PMPA. Unfortunately, the favourable interaction between 2-PMPA and valproate was associated with a pharmacokinetic increase in total brain valproate concentrations.     

The interactions of atorvastatin and fluvastatin with carbamazepine, phenytoin and valproate in the mouse maximal electroshock seizure model

The aim of this study was to determine the influence of acute (single) and chronic (once daily for 7 consecutive days) treatments with atorvastatin and fluvastatin on the anticonvulsant potential of three antiepileptic drugs: carbamazepine, phenytoin and valproate in the mouse maximal electroshock-induced seizure model. Additionally, the effects of acute and chronic administration of both statins on the adverse effect potential of three antiepileptic drugs were assessed in the chimney test (motor performance) and passive avoidance task (long-term memory). To evaluate the pharmacokinetic characteristics of interaction between antiepileptic drugs and statins, the total brain concentrations of antiepileptic drugs were estimated with the fluorescence polarization immunoassay technique. Results indicate that atorvastatin at doses up to 80mg/kg in chronic experiment attenuated the anticonvulsant potential of carbamazepine by increasing its ED(50) value against maximal electroconvulsions. Acute fluvastatin (80mg/kg) enhanced the anticonvulsant potential of carbamazepine and valproate by decreasing their ED(50) values. Acute fluvastatin (80mg/kg) also markedly increased the total brain carbamazepine concentration by 61% in a pharmacokinetic reaction. Atorvastatin (acute and chronic) and fluvastatin (chronic) in combinations with valproate impaired long-term memory in mice. Both statins in combinations with all three antiepileptic drugs had no impact on their adverse effects in the chimney test. Based on this preclinical study, one can conclude that chronic administration of atorvastatin reduces the anticonvulsant action of carbamazepine and acute fluvastatin can enhance the anticonvulsant potency of the carbamazepine and valproate. The former interaction was pharmacokinetic in nature.     

Cholecalciferol enhances the anticonvulsant effect of conventional antiepileptic drugs in the mouse model of maximal electroshock

The interactions between cholecalciferol, a precursor of the active form of Vitamin D(3), and conventional antiepileptic drugs (valproate, carbamazepine, phenytoin, and phenobarbital) were studied in the maximal electroshock test in mice. Vitamin D(3) applied i.p. at doses of 37.5 and 75 mug/kg, but not at 18.75 mug/kg, significantly raised the electroconvulsive threshold. Furthermore, cholecalciferol (at its highest subthreshold dose of 18.75 mug) potentiated the anticonvulsant activity of phenytoin and valproate. The action of carbamazepine and phenobarbital was also enhanced by Vitamin D(3), but when it was given at the higher dose of 37.5 mug/kg. Cholecalciferol, antiepileptic drugs, and their combinations did not produce significant adverse effects evaluated in the chimney test (motor coordination) and passive-avoidance task (long-term memory). Cholecalciferol did not significantly increase the brain concentrations of conventional antiepileptics, indicating a pharmacodynamic nature of revealed interactions. Our findings show that cholecalciferol may play an anticonvulsant role in the brain and can influence the efficacy of antiepileptic drugs, at least in experimental conditions.     

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.     

Effect of acutely and chronically administered venlafaxine on the anticonvulsant action of classical antiepileptic drugs in the mouse maximal electroshock model

The influence of acute and chronic treatments with intraperitoneal venlafaxine, a selective serotonin/norepinephrine reuptake inhibitor, on the anticonvulsant activity of selected antiepileptic drugs was studied in the maximal electroshock test in mice. Venlafaxine (12.5 and 25 mg/kg), given either acutely or chronically, significantly increased the electroconvulsive threshold. Moreover, both acute and chronic venlafaxine, applied at the highest subprotective dose of 6.25 mg/kg, enhanced the anticonvulsant effect of valproate, without affecting the protective action of carbamazepine, phenobarbital and phenytoin. The antidepressant did not affect brain concentration of valproate, indicating that the interaction between the two drugs seems pharmacodynamic in nature. Despite the lack of effect on the antielectroshock action of the remaining antiepileptics, acute venlafaxine increased the brain concentration of phenobarbital, while chronic venlafaxine reduced the brain level of phenytoin. In terms of adverse effects, acute/chronic venlafaxine and antiepileptic drugs alone, as well as their combinations, did not produce significant motor or long-term memory deficits in mice. Summing up, it seems that venlafaxine may be considered as a safe drug for the clinical use in patients with epilepsy and depressive disorders.     

Influence of 5-(3-chlorophenyl)-4-(4-methylphenyl)-2,4-dihydro-3H-1,2,4-triazole-3-thione on the anticonvulsant action of 4 classical antiepileptic drugs in the mouse maximal electroshock-induced seizure model

BackgroundThe aim of this study was to determine the effects of 5-(3-chlorophenyl)-4-(4-methylphenyl)-2,4-dihydro-3H-1,2,4-triazole-3-thione (TP10) on the protective action of 4 classical antiepileptic drugs – carbamazepine, phenobarbital, phenytoin and valproate – against maximal electroshock-induced seizures in mice.MethodsTonic hind limb extension (seizure activity) was evoked in adult male albino Swiss mice by an electric current (sine-wave, 25 mA, 500 V, 50 Hz, 0.2 s stimulus duration) delivered via auricular electrodes. Acute adverse-effect profiles with respect to motor performance, long-term memory and skeletal muscular strength were measured, together with total brain antiepileptic drug concentrations.ResultsTP10 administered intraperitoneally at 10 mg/kg significantly elevated the threshold for electroconvulsions in mice. TP10 at doses of 2.5 and 5 mg/kg had no impact on the threshold for electroconvulsions in mice. Moreover, TP10 (5 mg/kg) significantly enhanced the anticonvulsant activity of valproate, but not that of carbamazepine, phenobarbital or phenytoin in the maximal electroshock seizure test in mice. Pharmacokinetic experiments revealed that TP10 significantly elevated total brain concentrations of valproate in mice.ConclusionThe enhanced anticonvulsant action of valproate by TP10 in the mouse maximal electroshock-induced seizure model was associated with a pharmacokinetic increase in total brain valproate concentrations in mice. The combinations of TP10 with carbamazepine, phenobarbital and phenytoin were neutral from a preclinical viewpoint.     

Assessment of drug–drug interactions between moxonidine and antiepileptic drugs in the maximal electroshock seizure test in mice

Hypertension is a common comorbid condition with epilepsy, and drug interactions between antihypertensive and antiepileptic drugs (AEDs) are likely in patients. Experimental studies showed that centrally active imidazoline compounds belonging to antihypertensive drugs can affect seizure susceptibility. The purpose of this study was to assess the effect of moxonidine, an I₁-imidazoline receptor agonist, on the anticonvulsant efficacy of numerous AEDs (carbamazepine, phenobarbital, valproate, phenytoin, oxcarbazepine, topiramate and lamotrigine) in the mouse model of maximal electroshock. Besides, the combinations of moxonidine and AEDs were investigated for adverse effects in the passive avoidance task and the chimney test. Drugs were administered intraperitoneally (ip). Moxonidine at doses of 1 and 2 mg/kg ip did not affect the convulsive threshold. Among tested AEDs, moxonidine (2 mg/kg) potentiated the protective effect of valproate against maximal electroshock. This interaction could be pharmacodynamic because the brain concentration of valproate was not significantly changed by moxonidine. The antihypertensive drug did not cause adverse effects when combined with AEDs. This study shows that moxonidine may have a neutral or positive effect on the anticonvulsant activity of AEDs in patients with epilepsy. The enhancement of the anticonvulsant action of valproate by moxonidine needs further investigations to elucidate potential mechanisms involved.     

Topiramate potentiates the antiseizure activity of some anticonvulsants in DBA/2 mice

Topiramate (1-50 mg/kg, intraperitoneally (i.p.)) was able to antagonize audiogenic seizures in DBA/2 mice in a dose-dependent manner. Topiramate at dose of 2.5 mg/kg i.p., which per se did not significantly affect the occurrence of audiogenic seizures in DBA/2 mice, potentiated the anticonvulsant activity of carbamazepine, diazepam, felbamate, lamotrigine, phenytoin, phenobarbital and valproate against sound-induced seizures in DBA/2 mice. The degree of potentiation induced by topiramate was greatest for diazepam, phenobarbital and valproate, less for lamotrigine and phenytoin and not significant for carbamazepine and felbamate. The increase in anticonvulsant activity was associated with a comparable increase in motor impairment. However, the therapeutic index of the combination of all drugs+topiramate was more favourable than that of antiepileptics+ saline, with the exception of carbamazepine or felbamate+topiramate. Since topiramate did not significantly influence the total and free plasma levels of the anticonvulsant drugs studied, we suggest that pharmacokinetic interactions, in terms of total or free plasma levels, are not probable. However, the possibility that topiramate can modify the clearance from the brain of the anticonvulsant drugs studied cannot be excluded. In addition, topiramate did not significantly affect the hypothermic effects of the anticonvulsants tested. In conclusion, topiramate showed an additive effect when administered in combination with some classical anticonvulsants, most notably diazepam, phenobarbital, lamotrigine, phenytoin and valproate.     

New derivative of 1,2,4-triazole-3-thione (TP427) potentiates the anticonvulsant action of valproate,but not that of carbamazepine,phenytoin or phenobarbital in the mouse tonic-clonic seizure model

Background

To assess the effects of 5-(3-chlorobenzyl)-4-hexyl-2,4-dihydro-3H-1,2,4-triazole-3-thione (TP427) on the protective anticonvulsant action of four classical antiepileptic drugs (carbamazepine, phenobarbital, phenytoin and valproate) in the tonic-clonic seizure model in mice, an isobolographic transformation of data was used.

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.     

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.     

2-Chloro-N6-cyclopentyladenosine enhances the anticonvulsant action of carbamazepine in the mouse maximal electroshock-induced seizure model

This study examines the anticonvulsant profile of interactions between 2-chloro-N6-cyclopentyladenosine (CCPA, a selective adenosine A1 receptor agonist) and four conventional antiepileptic drugs (AEDs: carbamazepine--CBZ, phenobarbital, phenytoin and valproate) in the mouse maximal electroshock seizure (MES) model. Acute adverse effects produced by AEDs in combination with CCPA were determined in the chimney test (motor performance) and passive avoidance task (long-term memory). Results indicate that CCPA administered alone at 0.25 and 0.5 mg/kg significantly elevated the electroconvulsive threshold in mice. Additionally, the agent at a sub-threshold dose of 0.125 mg/kg potentiated the anticonvulsant activity of CBZ by reducing its ED50 in the MES test from 11.2 to 7.7 mg/kg (p < 0.01). In contrast, 8-cyclopentyl-1,3-dimethylxanthine (DPCPX, a selective adenosine A1 receptor antagonist at 5 mg/kg) abolished the enhanced anticonvulsant effects offered by the combination of CBZ with CCPA (0.125 mg/kg). Moreover, CCPA (0.125 mg/kg) co-administered with other tested AEDs had no significant impact on their antiseizure properties in the MES test in mice. Neither CCPA (0.125 mg/kg) administered singly, nor in combinations with conventional AEDs (at their ED50s) affected motor performance in the chimney test and long-term memory in the passive avoidance task. No pharmacokinetic alterations in brain CBZ concentrations were observed after administration of CCPA at 0.125 mg/kg. It may be concluded that CCPA, acting selectively on adenosine A1 receptors, enhances pharmacodynamically the antiseizure effect of CBZ in the MES test.     

Trazodone reduces the anticonvulsant action of certain classical antiepileptics in the mouse maximal electroshock model

BackgroundThe aim of the study was to examine effects of an acute and chronic treatment with trazodone, a serotonin antagonist and reuptake inhibitor (SARI), on the protective activity of four classical antiepileptic drugs provided in the maximal electroshock test in mice.MethodsElectroconvulsions were produced in mice by means of an alternating current (50 Hz, 25 mA, 0.2 s) and delivered via earclip electrodes. Motor impairment in animals were assessed in the chimney test, and long-term memory deficits were quantified in the passive-avoidance task. Brain concentrations of antiepileptic drugs were analyzed by fluorescence polarization immunoassay.ResultsThe obtained results showed that a single administration of trazodone (up to 40 mg/kg) did not influence the electroconvulsive threshold. In contrast, chronic treatment with the antidepressant (40 mg/kg) significantly increased this parameter. Furthermore, both single and chronic administration of trazodone reduced the anticonvulsant effect of phenytoin and carbamazepine against the maximal electroshock. However, the antidepressant remained without effect on the anticonvulsant action of valproate and phenobarbital. Some interactions between trazodone and antiepileptic drugs may have a pharmacodynamic background. Both, acute and chronic treatment with the antidepressant diminished the brain concentration of phenytoin. Chronic trazodone lowered the brain levels of carbamazepine and phenobarbital. Moreover, acute and chronic trazodone increased the valproate concentration in the brain. As regards undesired effects, acute and chronic trazodone (40 mg/kg), alone and in combination with phenytoin, significantly impaired long-term memory in tested animals, evaluated in the passive avoidance task. Acute trazodone (40 mg/kg) alone and combined with phenytoin produced also significant motor deficits in mice, as measured in the chimney test.ConclusionThe obtained results allow to conclude that trazodone is not a good candidate for an antidepressant drug in epileptic patients.