Pharmacodynamic and pharmacokinetic characterization of interactions between levetiracetam and numerous antiepileptic drugs in the mouse maximal electroshock seizure model: an isobolographic analysis

PURPOSE: Approximately 30% of patients with epilepsy do not experience satisfactory seizure control with antiepileptic drug (AED) monotherapy and often require polytherapy. The potential usefulness of AED combinations, in terms of efficacy and adverse effects, is therefore of major importance. The present study sought to identify potentially useful AED combinations with levetiracetam (LEV) METHODS: With isobolographic analysis, the mouse maximal electroshock (MES)-induced seizure model was investigated with regard to the anticonvulsant effects of carbamazepine (CBZ), phenytoin, phenobarbital (PB), valproate, lamotrigine, topiramate (TPM), and oxcarbazepine (OXC), administered singly and in combination with LEV. Acute adverse effects were ascertained by use of the chimney test evaluating motor performance and the step-through passive-avoidance task assessing long-term memory. Brain AED concentrations were determined to ascertain any pharmacokinetic contribution to the observed antiseizure effect. RESULTS: LEV in combination with TPM, at the fixed ratios of 1:2, 1:1, 2:1, and 4:1, was supraadditive (synergistic) in the MES test. Likewise, the combination of LEV with CBZ (at the fixed ratio of 16:1) and LEV with OXC (8:1 and 16:1) were supraadditive. In contrast, all other LEV/AED combinations displayed additivity. Furthermore, none of the investigated LEV/AED combinations altered motor performance and long-term memory. LEV brain concentrations were unaffected by concomitant AED administration, and LEV had no significant effect on brain concentrations of concomitant AEDs. CONCLUSIONS: These preclinical data would suggest that LEV in combination with TPM is associated with beneficial anticonvulsant pharmacodynamic interactions. Similar, but less profound effects were seen with OXC and CBZ.     

Levetiracetam and felbamate interact both pharmacodynamically and pharmacokinetically: an isobolographic analysis in the mouse maximal electroshock model

PURPOSE: Polytherapy with two or more antiepileptic drugs (AEDs) is generally required for approximately 30% of patients with epilepsy, who do not respond satisfactorily to monotherapy. The potential usefulness of AED combinations, producing synergistic anticonvulsant efficacy and minimal adverse effects, is therefore of significant importance. The present study sought to ascertain the potential usefulness of levetiracetam (LEV) and felbamate (FBM) in combination in the mouse maximal electroshock (MES)-induced seizure model. METHODS: The anticonvulsant interaction profile between LEV and FBM in the mouse MES-induced seizure model was determined using type II isobolographic analysis. Acute adverse effects (motor performance) were ascertained by use of the chimney test. LEV and FBM brain concentrations were measured by HPLC in order to determine any pharmacokinetic contribution to the observed antiseizure effect. RESULTS: LEV in combination with FBM, at the fixed ratios of 1:2, 1:1, 2:1, and 4:1, were supraadditive, whereas at the fixed ratio of 1:4, additivity was observed in the mouse MES model. Furthermore, none of the investigated combinations altered motor performance in the chimney test. Brain FBM concentrations were unaffected by concomitant LEV administration. In contrast, FBM significantly increased LEV brain concentrations. CONCLUSIONS: LEV in combination with FBM was associated with pharmacodynamic supraadditivity in the MES test. However, this anticonvulsant supraadditivity was associated with a concurrent increase in brain LEV concentrations indicating a pharmacokinetic contribution to the observed pharmacodynamic interaction between LEV and FBM.     

7-Nitroindazole potentiates the anticonvulsant action of some second-generation antiepileptic drugs in the mouse maximal electroshock-induced seizure model

Summary. The effects of 7-nitroindazole (7NI, a preferential neuronal nitric oxide synthase inhibitor) on the anticonvulsant activity of four second-generation antiepileptic drugs (AEDs: felbamate [FBM], lamotrigine [LTG], oxcarbazepine [OXC] and topiramate [TPM]) were studied in the mouse maximal electroshock-induced seizure (MES) model. Moreover, the influence of 7NI on the acute neurotoxic (adverse-effect) profiles of the studied AEDs, with regard to motor coordination, was determined in the chimney test in mice. Results indicate that 7NI (50 mg/kg; i.p.) significantly potentiated the anticonvulsant activity of OXC, but not that of FBM, LTG and TPM against MES-induced seizures and, simultaneously, it enhanced the acute neurotoxic effects of TPM, but not those of FBM, LTG and OXC in the chimney test in mice. 7NI at the lower dose of 25 mg/kg had no effect on the antiseizure activity and acute neurotoxic profiles of all investigated AEDs. Pharmacokinetic evaluation of interactions between 7NI and LTG, OXC and TPM against MES-induced seizures revealed no significant changes in free (non-protein bound) plasma AED concentrations following 7NI administration. Moreover, none of the examined combinations of 7NI with AEDs from the MES test were associated with long-term memory impairment in mice subjected to the step-through passive avoidance task. Based on our preclinical study, it can be concluded that only the combination of 7NI with OXC was beneficial, when considering its both anticonvulsant and acute neurotoxic effects. Moreover, the lack of impairment of long-term memory and no pharmacokinetic interactions in plasma of experimental animals make the combination of 7NI with OXC worthy of consideration for the treatment of patients with refractory epilepsy. The other combinations tested between 7NI and LTG, FBM and TPM were neutral, when considering their both anticonvulsant effects and acute neurotoxic profiles, therefore, no useful recommendation can be made for their clinical application.     

Effect of sildenafil on the anticonvulsant action of classical and second‐generation antiepileptic drugs in maximal electroshock‐induced seizures in mice

Purpose: The goal of the present study was to evaluate the effects of sildenafil on the threshold for electrically induced seizures in mice. In addition, interactions between sildenafil and classical and second‐generation antiepileptic drugs (AEDs), that is, carbamazepine (CBZ), phenobarbital (PB), phenytoin (PHT), valproate (VPA), lamotrigine (LTG), topiramate (TPM), and oxcarbazepine (OXC) were evaluated. Methods: Two electroconvulsive tests were used: maximal electroshock seizure threshold (MEST) and maximal electroshock seizure (MES) tests in mice. Acute adverse effects of the studied combinations were investigated in the chimney test, step‐through passive avoidance task, and grip‐strength test. Total brain and free plasma concentrations of AEDs were also determined. Results: Sildenafil raised the threshold for electroconvulsions in a dose‐dependent manner. It also increased the anticonvulsant activity of CBZ, VPA, and TPM in the MES test, whereas the activity of the remaining AEDs was not significantly changed. Sildenafil increased total brain and free (protein unbound) plasma CBZ concentrations and total brain VPA concentration. Neither sildenafil nor its coadministration with the studied AEDs affected motor coordination and long‐term memory in mice. Interestingly, sildenafil dose‐dependently enhanced the skeletal muscle strength in mice, although combinations of sildenafil with AEDs were ineffective in this respect. Conclusions: Sildenafil significantly raised the threshold for electroconvulsions in mice without any impairment of motor performance and long‐term memory, but it enhanced muscle strength. Treatment of patients on CBZ or VPA with sildenafil may not be recommended due to pharmacokinetic interactions. Coadministration of sildenafil with other AEDs, especially with TPM, seems to be a reasonable choice.     

Preclinical profile of combinations of some second-generation antiepileptic drugs: an isobolographic analysis

PURPOSE: The need for an efficacious treatment of patients with intractable seizures is urgent and pressing, because approximately 30% of epilepsy patients worldwide are still inadequately medicated with current frontline antiepileptic drugs (AEDs). This study sought to determine the interactions among some newer AEDs [topiramate (TPM), felbamate (FBM), oxcarbazepine (OXC), and lamotrigine (LTG)] in the maximal electroshock-induced seizures (MES) and chimney test (motor performance) in mice, by using the isobolographic analysis. METHODS: Evaluation of the anticonvulsant and acute adverse (neurotoxic) effects in mice produced by the AEDs in combinations at the fixed ratios of 1:3, 1:1, and 3:1 allowed the assessment of their preclinical profile and the determination of benefit indices (BIs) for all individual combinations. RESULTS: Combinations of TPM+FBM at the fixed ratios of 1:3, 1:1, and 3:1 offered supraadditive (synergistic) interactions against electroconvulsions and subadditivity (antagonism) in terms of acute neurotoxic effects in the chimney test (BIs ranged between 1.90 and 2.59, the best combinations from a preclinical point of view). The examined combinations of TPM+OXC also were advantageous due to synergistic interactions in the MES, and additivity in terms of acute neurotoxic effects produced by the AEDs (BIs ranged between 1.35 and 1.71). In contrast, OXC+FBM exerted subadditive (antagonistic) interactions in the MES test and additive interactions in terms of acute motor impairment of animals (BIs ranged between 0.53 and 0.71). The worst combination was observed for OXC+LTG, at the fixed ratio of 1:1, displaying subadditivity (antagonism) against electroconvulsions and supraadditivity (synergy) with respect to neurotoxicity (BIs, 0.43). The remaining combinations of OXC+LTG tested (i.e., 1:3 and 3:1) exerted additivity in the MES test and supraadditivity in the chimney test (BIs 0.54 and 0.49, respectively). None of the studied AEDs affected the brain concentrations of other AEDs, so the existence of any pharmacokinetic interactions to be responsible for the observed effects is improbable. CONCLUSIONS: Based on the current preclinical data, the pharmacological profile of combinations of TPM+FBM and TPM+OXC evaluated with isobolography was beneficial and might be worth recommendation to further clinical practice. In contrast, utmost caution is required during the use of OXC+FBM or OXC+LTG in clinical practice, because of the high risk of neurotoxic adverse effect appearance.     

Pharmacodynamic and pharmacokinetic interactions between common antiepileptic drugs and acetone, the chief anticonvulsant ketone body elevated in the ketogenic diet in mice

Purpose:   Acetone is the principal ketone body elevated in the ketogenic diet (KD), with demonstrated robust anticonvulsant properties across a variety of seizure tests and models of epilepsy. Because the majority of patients continue to receive antiepileptic drugs (AEDs) during KD treatment, interactions between acetone and AEDs may have important clinical implications. Therefore, we investigated whether acetone could affect the anticonvulsant activity and pharmacokinetic properties of several AEDs against maximal electroshock (MES)–induced seizures in mice.
Methods:   Effects of acetone given in subthreshold doses were tested on the anticonvulsant effects of carbamazepine (CBZ), lamotrigine (LTG), oxcarbazepine (OXC), phenobarbital (PB), phenytoin (PHT), topiramate (TPM) and valproate (VPA) against MES-induced seizures in mice. In addition, acute adverse effects of acetone–AEDs combinations were assessed in the chimney test (motor performance) and passive avoidance task (long-term memory). Pharmacokinetic interactions between acetone and AEDs were also studied in the mouse brain tissue.
Results:   Acetone (5 or 7.5 mmol/kg, intraperitoneally [i.p.]) enhanced the anticonvulsant activity of CBZ, LTG, PB, and VPA against MES-induced seizures; effects of OXC, PHT, and TPM were not changed. Acetone (7.5 mmol/kg) did not enhance the acute adverse-effect profiles of the studied AEDs. Acetone (5 or 7.5 mmol/kg, i.p.) did not affect total brain concentrations of the studied AEDs. In contrast, VPA, CBZ, LTG, OXC, and TPM significantly decreased the concentration of free acetone in the brain; PB and PHT had no effect.
Conclusions:   Acetone enhances the anticonvulsant effects of several AEDs such as VPA, CBZ, LTG, and PB without affecting their pharmacokinetic and side-effect profiles.     

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

Purpose: The study investigated the types of interactions between lamotrigine (LTG) and first-generation antiepileptic drugs (AEDs) or topiramate (TPM) with isobolographic analysis. Methods: Anticonvulsant and adverse-effect profiles of combinations of LTG with other AEDs, at fixed ratios of 1:3, 1:1, and 3:1, were evaluated in the maximal electroshock (MES)-induced seizures and the chimney test (motor performance) in mice, which allowed the determination of benefit indices (BIs) for individual combinations. Results: Combinations of LTG with TPM or valproate (VPA), at fixed ratios of 1:1, were significantly supraadditive (synergistic) in the MES test and, simultaneously, subadditive (antagonistic) in the chimney test, showing the best profile for AED combinations. In contrast, combinations between LTG and carbamazepine (CBZ), in terms of antiseizure protection against MES, were subadditive (antagonistic) and additive in the chimney test, resulting in unfavorable AED combinations. Moreover, the combination of LTG with phenobarbital (PB), at a fixed ratio of 1:1, despite synergy in the MES test, also was synergistic in the chimney test, resulting in a modest BI for AED combination. LTG combined with phenytoin was additive in both the MES and chimney tests in mice. The remaining combinations, at fixed ratios not mentioned earlier, also showed an average BI for AED combinations. Furthermore, LTG combined with all studied AEDs did not affect long-term memory in mice. None of the AEDs influenced the free plasma level of LTG, whereas LTG slightly reduced the free plasma concentration of PB. Conclusions: Interactions between LTG and TPM or LTG and VPA at a fixed ratio of 1:1 might be profitable from a preclinical point of view, displaying the most optimal BI.     

Amiloride enhances the anticonvulsant action of various antiepileptic drugs in the mouse maximal electroshock seizure model

Accumulating evidence indicates that amiloride (a potassium-sparing diuretic) exerts the anticonvulsant action in various in vivo and in vitro experiments. Therefore, the objective of this study was to assess the influence of amiloride on the protective action of numerous conventional and second-generation antiepileptic drugs [AEDs: carbamazepine (CBZ), lamotrigine (LTG), oxcarbazepine (OXC), phenobarbital (PB), topiramate (TPM), and valproate (VPA)] against maximal electroshock (MES)-induced seizures in mice. Results indicate that amiloride [up to 100 mg/kg, intraperitoneally (i.p.), at 30, 60, and 120 min before the test] neither altered the threshold for electroconvulsions, nor protected the animals against MES-induced seizures in mice. Moreover, amiloride (75 and 100 mg/kg, i.p., 120 min prior to the test) significantly enhanced the anticonvulsant effects of all studied AEDs, except for LTG, by reducing their ED₅₀ values in the MES test. In contrast, amiloride at 50 mg/kg (i.p.) had no significant effect on the antielectroshock action of the tested AEDs in mice. Estimation of total brain AED concentrations revealed that amiloride (75 mg/kg) significantly increased total brain concentrations of CBZ, OXC, and PB, but not those of LTG, TPM, and VPA in mice. In conclusion, one can ascertain that the potentiation of the antiseizure action of TPM and VPA by amiloride in the MES test and lack of any pharmacokinetic interactions between drugs, make the combinations of amiloride with TPM and VPA of pivotal importance for epileptic patients.     

Effect of topiramate on the anticonvulsant activity of conventional antiepileptic drugs in two models of experimental epilepsy

PURPOSE: The objective of this study was to evaluate the interaction of the novel antiepileptic drug (AED), topiramate (TPM), with conventional AEDs against amygdala-kindled seizures in rats and pentylenetetrazol-induced convulsions in mice. METHODS: Experiments were performed on mice and fully kindled rats. In pentylenetetrazol test, the chemoconvulsant was used at its CD97 dose of 105 mg/kg, producing clonic seizures in 97% of mice. Adverse effects were evaluated with the chimney test and passive avoidance task. Plasma levels of AEDs were measured with immunofluorescence. RESULTS: TPM at 20 mg/kg exerted a significant anticonvulsant effect as regards seizure and afterdischarge durations in amygdala-kindled seizures in rats, being ineffective at lower doses. Coadministration of TPM (10 mg/kg) with valproate (VPA; at a subtherapeutic dose of 50 mg/kg) resulted in essential reductions of seizure and afterdischarge durations. TPM (10 mg/kg) combined with carbamazepine (CBZ; at a subtherapeutic dose of 15 mg/kg) significantly increased afterdischarge threshold, simultaneously decreasing the remaining seizure parameters (duration or severity of seizures and afterdischarge duration). TPM (10 mg/kg) given with phenobarbital (PB; 15 mg/kg) markedly shortened seizure severity and seizure and afterdischarge durations. Combinations of TPM with diphenylhydantoin (PHT) were ineffective against kindled seizures in rats. TPM combined with VPA and PB did not alter their plasma levels, but its combination with CBZ resulted in an increased free plasma CBZ concentration. TPM (10 and 20 mg/kg) alone and its combinations with conventional AEDs affected neither motor coordination nor long-term memory, evaluated in the chimney and passive avoidance tests, respectively, in rats. In pentylenetetrazol-evoked convulsions in mice, TPM (175 and 200 mg/kg) showed anticonvulsant effects per se. Moreover, TPM (at its subtherapeutic dose of 150 mg/kg), significantly potentiated the anticonvulsant action of ethosuximide (ESM), but not that of VPA, PB, or clonazepam (CZP) against pentylenetetrazol-induced seizures. Either TPM alone (150 mg/kg) or its combination with ESM did not result in significant undesired effects. CONCLUSIONS: The experimental data indicate that except for PHT, the combinations of TPM with conventional AEDs are beneficial against amygdala-kindled seizures in rats. In the pentylenetetrazol test, this novel AED potentiated only the protection offered by ESM.     

Pharmacodynamic and pharmacokinetic interaction studies of loreclezole with felbamate, lamotrigine, topiramate, and oxcarbazepine in the mouse maximal electroshock seizure model

PURPOSE: The study investigated the types of interactions between loreclezole (LCZ) and a variety of newly licensed antiepileptic drugs (AEDs) with different mechanisms of actions [felbamate (FBM), lamotrigine (LTG), topiramate (TPM), and oxcarbazepine (OXC)] by isobolographic analysis. METHODS: Anticonvulsant and adverse-effect profiles of combinations of LCZ with other AEDs at fixed ratios of 1:3, 1:1, and 3:1 were investigated in the maximal electroshock (MES)-induced seizures and the chimney test (as a measure of motor impairment) in mice so as to identify optimal combinations. Protective indices (PIs) and benefit indices (BIs) were calculated so that a ranking in relation to advantageous combinations could be established. RESULTS: With isobolography, it was observed that the combination of LCZ and TPM, at the fixed ratios of 1:1 and 3:1, was supraadditive (synergistic; p < 0.05), whereas LCZ with TPM at the fixed ratio of 1:3 and LCZ combined with LTG, FBM, or OXC at the fixed ratios of 1:3, 1:1, and 3:1 were associated with additive interactions. Moreover, the isobolographic analysis in the chimney test revealed that only one combination tested (LCZ and TPM at the fixed ratio of 1:1) was subadditive (antagonistic; p < 0.05), whereas the remaining combinations of LCZ with LTG, FBM, or OXC (at the fixed ratios of 1:3, 1:1, and 3:1) barely displayed additivity. However, these combinations were associated with significant pharmacokinetic interactions, in that LCZ increased brain TPM (94%), OXC (21%), FBM (46%), and LTG (8%) concentrations. In addition, brain LCZ concentrations were decreased by TPM (26%), OXC (37%), LTG (42%), and FBM (19%). None of the examined combinations between LCZ and TPM, OXC, LTG, and FBM altered long-term memory in the step-through passive-avoidance task. CONCLUSIONS: LCZ plus TPM appears to be a particularly favorable combination, based on the MES test and the chimney test. LCZ and OXC also is a favorable combination. However, these conclusions are confounded by the fact that LCZ is associated with significant pharmacokinetic interactions.     

Furosemide potentiates the anticonvulsant action of valproate in the mouse maximal electroshock seizure model

Accumulating evidence indicates that furosemide (FUR, a loop diuretic) exerts the anticonvulsant action in various in vitro and in vivo experiments. Therefore, the aim of this study was to assess the influence of FUR on the protective action of numerous conventional and newer antiepileptic drugs (carbamazepine [CBZ], lamotrigine [LTG], oxcarbazepine [OXC], phenobarbital [PB], topiramate [TPM] and valproate [VPA]) in the mouse maximal electroshock seizure (MES) model. Results indicate that FUR (up to 100mg/kg, i.p., 30 min before the test) neither altered the threshold for electroconvulsions nor protected the animals against MES-induced seizures in mice. FUR (100 mg/kg, i.p.) enhanced the anticonvulsant effects of VPA in the MES test by reducing its ED(50) value from 230.4 to 185.4 mg/kg (P<0.05). In contrast, FUR at 100 mg/kg had no significant effect on the antielectroshock action of the remaining drugs tested (CBZ, LTG, OXC, PB, and TPM) in mice. Estimation of free plasma and total brain VPA concentrations revealed that the observed interaction between FUR and VPA in the MES test was pharmacodynamic in nature because neither free plasma nor total brain VPA concentrations were altered after i.p. administration of FUR. In conclusion, one can ascertain that the selective potentiation of the antielectroshock action of VPA by FUR and lack of any pharmacokinetic interactions between drugs, make this combination of pivotal importance for epileptic patients treated with VPA and received FUR from other than epilepsy reasons.     

Isobolographic characterization of interactions of levetiracetam with the various antiepileptic drugs in the mouse 6 Hz psychomotor seizure model

The aim of this study was to characterize the anticonvulsant effects of levetiracetam (LEV) in combination with the various antiepileptic drugs (clonazepam [CZP], oxcarbazepine [OXC], phenobarbital [PB], tiagabine [TGB], and valproate [VPA]), in the mouse 6 Hz psychomotor seizure model.Limbic (psychomotor) seizure activity was evoked in albino Swiss mice by a current (32 mA, 6 Hz, 3 s stimulus duration) delivered via ocular electrodes and isobolographic analysis for parallel and non-parallel dose–response effects was used to characterize the consequent anticonvulsant interactions between the various drug combinations. Potential concurrent adverse-effect profiles of interactions between LEV and CZP, OXC, PB, TGB, and VPA at the fixed-ratio of 1:1 were evaluated in the chimney (motor performance), passive avoidance (long-term memory), and grip-strength (muscular strength) tests.LEV administered singly was associated with a dose–response relationship curve (DRRC) that was parallel to that for CZP and non-parallel to that for OXC, PB, TGB and VPA. With isobolography for parallel DRRCs, the combination of LEV with CZP at three fixed-ratios of 1:3, 1:1 and 3:1 was additive in nature. With isobolography for non-parallel DRRCs the combinations of LEV with OXC, TGB and VPA at the fixed-ratio of 1:1 were also additive. In contrast, the isobolography for non-parallel DRRCs revealed that the interaction for the combination of LEV with PB at the fixed-ratio of 1:1 was supra-additive (synergistic). None of the combinations were associated with any concurrent adverse effects with regards to motor coordination, long-term memory or muscular strength.LEV is associated with favorable anticonvulsant synergism with PB and is additive with regards to CZP, OXC, TGB and VPA in the mouse 6 Hz psychomotor seizure model.     

Agmatine enhances the anticonvulsant action of phenobarbital and valproate in the mouse maximal electroshock seizure model

Accumulating evidence indicates that agmatine (AGM—an endogenous neuromodulator/neurotransmitter in the brain) exerts the anticonvulsant action in various in vivo experiments. Therefore, the aim of this study was to assess the influence of AGM on the protective action of numerous conventional and newer antiepileptic drugs [carbamazepine (CBZ), lamotrigine (LTG), oxcarbazepine (OXC), phenobarbital (PB), phenytoin (PHT), topiramate (TPM) and valproate (VPA)] in the mouse maximal electroshock seizure (MES) model. Results indicate that AGM (up to 100 mg/kg, i.p., 45 min before the test) neither altered the threshold for electroconvulsions nor protected the animals against MES-induced seizures in mice. Moreover, AGM (100 mg/kg, i.p.) significantly enhanced the anticonvulsant effects of PB and VPA in the MES test by reducing their ED₅₀ values from 22.54 to 16.82 mg/kg (P < 0.01) for PB, and from 256.1 to 210.6 mg/kg (P < 0.05) for VPA, respectively. In contrast, AGM at 100 mg/kg (i.p.) had no significant effect on the antielectroshock action of the remaining drugs tested (CBZ, LTG, OXC, PHT, and TPM) in mice. Estimation of total brain PB and VPA concentrations revealed that the observed interactions between AGM and PB or VPA in the MES test were pharmacodynamic in nature because neither total brain PB, nor total brain VPA concentrations were altered after i.p. administration of AGM at 100 mg/kg. Moreover, none of the examined combinations of AGM (100 mg/kg) with CBZ, LTG, OXC, PB, PHT, TPM, and VPA (at their ED₅₀ values from the MES test) affected motor coordination in the chimney test, long-term memory in the passive avoidance task, and muscular strength in the grip-strength test in mice, indicating no acute adverse effects in animals. In conclusion, one can ascertain that the selective potentiation of the antielectroshock action of PB and VPA by AGM, lack of any pharmacokinetic interactions between drugs and no acute adverse effects, make the combinations of AGM with PB or VPA of pivotal importance for epileptic patients. It seems that modulation of AGM concentration in the brain may occur favorable in further clinical practice. The results of this study were presented in part at the “11th Congress of the European Federation of Neurological Societies” Brussels, Belgium, 25–28 August, 2007 [abstract in 2007, Eur J Neurol 14(Suppl 1):210].     

Pharmacodynamic interaction studies with topiramate in the pentylenetetrazol and maximal electroshock seizure models.

There is emerging evidence to support the efficacy of some antiepileptic drug (AED) combinations in refractory epilepsy. Definitive clinical studies are, however, difficult to perform. Experimental seizure models can be employed to identify potentially useful combinations for subsequent clinical evaluation. We have investigated the anticonvulsant effects of topiramate (TPM) in combination with 13 other AEDs in the pentylenetetrazol (PTZ) and maximal electroshock (MES) seizure models. Single drugs and combinations were administered by intraperitoneal injection and anticonvulsant effects determined at 1-hour post-dosing. TPM was without significant effect in the PTZ test. In contrast, phenobarbital, primidone, ethosuximide, sodium valproate, felbamate and tiagabine all increased the latency to the first generalised seizure. Combinations of TPM and active adjunctive drug were universally effective. Combinations of TPM with clobazam, lamotrigine and levetiracetam were also anticonvulsant, despite the inactivity of the constituent compounds when administered alone. TPM reduced the incidence of MES-induced seizures in a dose-dependent manner, as did phenobarbital, phenytoin, primidone, carbamazepine, sodium valproate, clobazam, lamotrigine, felbamate and tiagabine. All combination treatments were similarly effective. These findings suggest that combinations of TPM with lamotrigine and levetiracetam may demonstrate anticonvulsant synergism and merit further investigation in additional model systems and with recourse to more quantitative mathematical analysis.     

Comparative retention rates and long-term tolerability of new antiepileptic drugs.

OBJECTIVE: Retention rates of five new anti-epileptic medications (AEDs) were compared in order to evaluate their long-term tolerability and efficacy. METHOD: We acquired the retention data on levetiracetam (LEV), lamotrigine (LTG), oxcarbazepine (OXC), topiramate (TPM), and zonisamide (ZNS) from the electronic database. The data included patient's age, gender, seizure type, current and previous medications, dosage, main reasons for discontinuation, and duration of therapy. The retention rates of these AEDs were evaluated at 4, 12, 24, 52, and 104 weeks. RESULTS: A total of 828 new AED exposures were obtained (LEV=196, LTG=251, OXC=97, TPM=156, ZNS=128) from patients with partial or generalized epilepsy. At 2 years, retention rate was highest with LTG (74.1%), followed by ZNS (60.2%), OXC (58.8%), LEV (53.6%), and TPM (44.2%). When these AEDs were discontinued, it was mainly due to inefficacy (29.5%) and sedating side-effects (20.5%), and commonly within 6 months into therapy. Several important AED specific side-effects leading to discontinuation were identified, including behavioral or irritability from LEV, rash from LTG and OXC, nausea from OXC and ZNS, hyponatremia from OXC, and kidney stones from TPM and ZNS. CONCLUSION: Comparing retention rates of new AEDs can provide useful insight into their tolerability and efficacy. This study showed highest retention rate with LTG, which was significantly different from ZNS (p=0.0025), LEV (p<0.0001), OXC (p=0.0024), and TPM (p<0.0001). Beside ineffectiveness, other leading causes of discontinuation were adverse behavioral effects with LEV, rash with LTG and OXC, and sedation for TPM and ZNS.     

Pharmacodynamic and pharmacokinetic interactions of perampanel and other antiepileptic drugs in a rat amygdala kindling model

PurposeThis study explored the pharmacodynamic and pharmacokinetic effects of combining perampanel (PER) with commonly co-administered AEDs.MethodA strong stimulus intensity (three-fold higher than after-discharge threshold) was used to elicit drug-resistant seizures in a rat amygdala kindling model. Vehicle, low-dose PER (0.75 mg/kg), or high-dose PER (1.5 mg/kg), in combination with vehicle, levetiracetam (LEV) 50 mg/kg, lamotrigine (LAM) 20 mg/kg, carbamazepine (CBZ) 20 mg/kg, or valproic acid (VPA) 200 mg/kg, were administered intraperitoneally to groups of 6–13 rats. Seizure score, electroencephalography (EEG) seizure duration, and motor seizure duration were evaluated, with pharmacodynamic interactions determined by two-way analysis of variance (ANOVA). Motor impairment was evaluated by rotarod test and two-way ANOVA.ResultsHigh-dose PER, but not low-dose PER, LEV, LAM, CBZ, or VPA, reduced EEG seizure duration, motor seizure duration, and seizure score compared with vehicle alone. However, when low-dose PER was administered in combination with LEV, LAM, CBZ, or VPA, seizure severity parameters were reduced compared with the concomitant AEDs alone. These pharmacodynamic interactions were statistically significant in some cases, but the same AED combinations were not associated with statistically significant neurotoxic interactions. Efficacy may have been slightly affected by changes in PER plasma concentrations in the presence of other AEDs:PER plasma concentrations increased with LEV or LAM co-administration, and decreased with CBZ or VPA co-administration.ConclusionOverall, these data support published Phase III data demonstrating the efficacy of PER as adjunctive therapy for the treatment of refractory partial-onset seizures in patients aged ≥12 years.     

Anticonvulsant properties of the novel nootropic agent nefiracetam in seizure models of mice and rats

PURPOSE: Nefiracetam (NEF) is a novel pyrrolidone-type nootropic agent, and it has been reported to possess various pharmacologic effects as well as cognition-enhancing effects. The present study focused on the anticonvulsant effect of NEF and its potential for antiepileptic therapy. METHODS: The anticonvulsant properties of NEF were investigated in experimental seizure models of mice and rats, compared with levetiracetam (LEV) and other standard antiepileptic drugs [AEDs; zonisamide (ZNS), phenytoin (PHT), carbamazepine (CBZ), valproic acid (VPA), diazepam (DZP), and ethosuximide (ESM)]. With reference to standard programs for evaluating potential AEDs, the study included the traditional maximal electroshock seizure and subcutaneous chemoconvulsant (pentylenetetrazole, bicuculline, picrotoxin, strychnine, or N-methyl-D-aspartate) seizure tests and two threshold models (the increasing-current electroshock seizure test and intravenous pentylenetetrazole seizure threshold test). Neurotoxic activities were examined with the rotarod test and traction test. RESULTS: NEF inhibited electroshock-induced seizures at nontoxic doses, whereas it had no effect on seizures chemically induced by pentylenetetrazole, bicuculline, picrotoxin, strychnine, or N-methyl-D-aspartate. The anticonvulsant spectrum of NEF paralleled that of ZNS, PHT, and CBZ. The anticonvulsant efficacy of NEF was comparable with that of ZNS and less potent than that of PHT, CBZ, and DZP. However, the safety margin of NEF was superior to that of ZNS, CBZ, VPA, and DZP. LEV showed only slight anticonvulsant effects in threshold models, and it was not effective in conventional screening models. CONCLUSIONS: These results suggest that NEF has distinct anticonvulsant spectrum and mechanisms from those of LEV. NEF is an orally active and safe AED, and it possesses a potential for antiepileptic therapy.     

Conversion from carbamazepine or oxcarbazepine to topiramate in adolescents and adults with epilepsy

Objective – To explore effectiveness, tolerability and changes in quality of life in patients with epilepsy converting to topiramate (TPM) from carbamazepine (CBZ) or oxcarbazepine (OXC) due to insufficient effectiveness and/or tolerability. Methods – A multicenter, open‐label, non‐interventional trial was used to examine patients (≥ 12 years) with epilepsy, changing to TPM monotherapy from baseline mono‐ or combination therapy with CBZ or OXC. TPM was added to the existing antiepileptic drug (AED) treatment and started at a dose of 25 mg once daily. The dose was titrated up with 25 mg/day increments, once every 1–2 weeks, until a final dose between 50 and 200 mg/day was reached. On the basis of clinical judgment, the treating physician decided whether or not the existing AED treatment with CBZ or OXC could then be withdrawn. Type and number of seizures, preferred TPM dose, quality of life (QOLIE‐10 questionnaire), subjective perception of improvement and adverse events (AE) were documented. Results – 140 patients (53.5% women, mean age 47 years) decided to switch to TPM due to insufficient effectiveness (75% of patients) and/or poor tolerability (80%) of the CBZ/OXC treatment. Average duration of follow‐up was 24 weeks with an overall discontinuation rate of 19.3%, mainly due to AEs (12.1%). At study endpoint, the intended shift to TPM monotherapy was achieved in 73% of patients at a median TPM dose of 100 mg/day. A seizure reduction of ≥ 50% was achieved in 91% of patients in the last scheduled period (weeks 12–26); 62% of patients entering that period remained seizure free. Quality of life at endpoint improved significantly when compared with baseline for all domains of QOLIE‐10 (P < 0.001). Most frequent AEs (reported by ≥ 5% of patients) were paresthesia (9.3%), weight loss (7.9%), convulsions (5.7%) and memory disorders (5.0%). Conclusion – In patients with epilepsy, previously not satisfactorily treated with CBZ or OXC, conversion to TPM may result in an improvement in seizure control as well as in quality of life.     

An In Vitro Study of New Antiepileptic Drugs and Astrocytes

Summary:  Purpose: The aim of our research was to study some biochemical modifications elicited in primary rat astrocyte cultures by treatment with gabapentin (GBP), carbamazepine (CBZ), lamotrigine (LTG), topiramate (TPM), oxcarbazepine (OXC), tiagabine (TGB), and levetiracetam (LEV), commonly used in the treatment of epilepsy. We investigated the biologic effects of these anticonvulsants (AEDs) at concentrations of 1, 10, 50, and 100 μg/ml.
Methods: The study was performed by examining cell viability (MTT assay), cell toxicity [lactate dehydrogenase (LDH) release in the medium], glutamine synthetase (GS) activity, reactive oxygen species (ROS) production, lipoperoxidation level (malondialdehyde; MDA), and DNA fragmentation (COMET assay). The level of the expression of 70-kDa heat-shock protein (HSP70) and inducible nitric oxide synthase (iNOS) as oxidative stress–modulated genes also was determined.
Results: Our experiments indicate that CBZ, TPM, and OXC induce stress on astrocytes at all concentrations. GBP, LTG, TGB, and LEV, at low concentrations, do not significantly change the metabolic activities examined and do not demonstrate toxic actions on astrocytes. They do so at higher concentrations.
Conclusions: Most AEDs have effects on glial cells and, when used at an appropriate cell-specific concentrations, may be well tolerated by cortical astrocytes. However, at higher concentrations, GBP, LTG, TGB, and LEV seem to be better tolerated than are CBZ, TPM, and OXC. These findings may reveal novel ways of producing large numbers of new AEDs capable of reducing the extent of inflammation, neuronal damage, and death under pathological conditions such as epilepsy and/or traumatic brain injury.