Antiepileptic drugs: safety in numbers?

Additive interactions of pregabalin with lamotrigine, oxcarbazepine and topiramate in the mouse maximal electroshock-induced seizure model: a type I isobolographic analysis for non-parallel dose-response relationship curves

The aim of this study was to characterize the anticonvulsant effects of pregabalin (PGB-a third-generation antiepileptic drug) in combination with three second-generation antiepileptic drugs (i.e., lamotrigine [LTG], oxcarbazepine [OXC] and topiramate [TPM]) in the mouse maximal electroshock (MES)-induced seizure model by using the type I isobolographic analysis for non-parallel dose-response relationship curves (DRRCs). Tonic hind limb extension (seizure activity) was evoked in adult male albino Swiss mice by a current (sine-wave, 25mA, 500V, 50Hz, 0.2s stimulus duration) delivered via auricular electrodes. Potential adverse-effect profiles of interactions of PGB with LTG, OXC and TPM at the fixed-ratio of 1:1 in the MES test with respect to motor performance, long-term memory and skeletal muscular strength were measured. In the mouse MES model, PGB administered singly had its DRRC non-parallel to that for LTG, OXC and TPM. With type I isobolography for non-parallel DRRCs, the combinations of PGB with LTG, OXC and TPM at the fixed-ratio of 1:1 exerted additive interaction. In all combinations, neither motor coordination, long-term memory nor muscular strength were affected. In conclusion, the additive interactions between PGB and LTG, OXC and TPM are worthy of consideration while extrapolating the results from this study to clinical settings.

Interaction of tiagabine with valproate in the mouse pentylenetetrazole-induced seizure model: an isobolographic analysis for non-parallel dose-response relationship curves

PURPOSE

To characterize the interaction between tiagabine (TGB) and valproate (VPA)--two antiepileptic drugs in the mouse pentylenetetrazole (PTZ)-induced clonic seizure model, type I isobolographic analysis for non-parallel dose-response relationship curves (DRRCs) was used.

MATERIAL AND METHODS

Clonic seizures were evoked in albino Swiss mice by subcutaneous injection of PTZ at its CD97 (100 mg/ kg). To ascertain the nature of interaction between TGB and VPA administered in combination, total brain concentrations of TGB and VPA were estimated by using high-performance liquid chromatography (HPLC) and fluorescence polarization immunoassay (FPIA).

RESULTS

TGB and VPA produced clear-cut anticonvulsant effects against PTZ-induced clonic seizures in mice and their DRRCs were not parallel to one another. The type I isobolographic analysis for non-parallel DRRCs revealed that the combination of TGB with VPA at the fixed-ratio of 1:1 exerted additive interaction against PTZ-induced clonic seizures in mice. With FPIA, it was found that TGB did not affect total brain VPA concentrations in experimental animals. Moreover, VPA had no significant impact on total brain concentrations of TGB in mice, as measured with HPLC.

CONCLUSION

The additive interaction between TGB and VPA at the fixed-ratio of 1:1 in the mouse PTZ model was pharmacodynamic in nature.

Isobolographic and behavioral characterizations of interactions between vigabatrin and gabapentin in two experimental models of epilepsy

The aim of this study was to characterize the pharmacodynamic, pharmacokinetic and adverse-effect profiles of vigabatrin and gabapentin. Isobolographic analysis was used in two mouse experimental models of epilepsy: the maximal electroshock seizure threshold test and pentylenetetrazole-induced seizures. In the maximal electroshock seizure threshold test, electroconvulsions were produced by a current with various intensities whilst in the pentylenetetrazole test a CD(97) dose (100 mg/kg) was used. Potential adverse-effect profiles of interactions of vigabatrin with gabapentin at three fixed-ratios of 1:3, 1:1 and 3:1 from both seizure tests were evaluated in the chimney (motor performance) and grip-strength (skeletal muscular strength) tests. Vigabatrin and gabapentin total brain concentrations were determined with high performance liquid chromatography. Vigabatrin and gabapentin administered singly increased the electroconvulsive threshold (TID(20) - 226.2 and 70.0 mg/kg, respectively). With isobolography, the combination of vigabatrin with gabapentin at the fixed-ratio of 1:3 exerted supra-additive (synergistic) interactions whilst at 1:1 and 3:1 additivity occurred. Similarly, vigabatrin and gabapentin administered singly suppressed the pentylenetetrazole-induced seizures (ED(50) values - 622.5 and 201.1 mg/kg, respectively). Isobolography revealed that vigabatrin with gabapentin in combination at the fixed-ratio of 1:1 produced supra-additive (synergistic) interaction whilst at 1:3 and 3:1 additivity occurred. In combination neither motor coordination nor skeletal muscular strength was affected. Total vigabatrin and gabapentin brain concentrations revealed that neither drug affected the pharmacokinetics of the other. Vigabatrin and gabapentin have a favorable pharmacodynamic interaction in animal seizure models in the absence of acute adverse effects or concurrent pharmacokinetic changes.

Interactions of tiagabine with ethosuximide in the mouse pentylenetetrazole-induced seizure model: an isobolographic analysis for non-parallel dose-response relationship curves

The aim of this study was to characterize the interaction between tiagabine (TGB) and ethosuximide (ETS), two antiepileptic drugs, in pentylenetetrazole (PTZ)-induced clonic seizures in mice using isobolographic analysis. The nature of the interaction between the drugs administered in combination was ascertained by estimating plasma and brain concentrations of ETS and TGB using fluorescence polarization immunoassay (FPIA) and high-performance liquid chromatography (HPLC). The results indicated that both drugs produced clear anticonvulsant effects against PTZ-induced clonic seizures in mice, but that their dose-response relationship curves (DRRCs) were not parallel, consequently necessitating the isobolographic analysis for non-parallel DRRCs. The isobolographic analysis revealed that the combination of TGB with ETS at the fixed-ratio of 1:1 exerted an additive interaction against PTZ-induced clonic seizures in mice. FPIA documented that TGB significantly elevated brain ETS concentrations (by 64%), while having no effect on plasma ETS concentrations in experimental animals. In contrast, ETS had no significant impact on plasma and brain concentrations of TGB in mice, as measured by HPLC. It can be concluded that the additive interaction between TGB and ETS at the fixed-ratio of 1:1 in the PTZ test was complicated by a significant pharmacokinetic increase in total brain ETS concentrations. At present, there are no recommendations to use this drug combination in epileptic patients.

Interactions of MRZ 2/576 with felbamate, lamotrigine, oxcarbazepine and topiramate in the mouse maximal electroshock-induced seizure model

This study focused on the evaluation of interactions between MRZ 2/576 (8-chloro-4-hydroxy-1-oxo-1,2-dihydropyridazino(4,5-b)quinoline-5-oxide choline salt), an N-methyl-D-aspartate (NMDA) receptor antagonist acting at the NMDA receptor/glycine(B) site and four newer antiepileptic drugs (felbamate, lamotrigine, oxcarbazepine, and topiramate) in the mouse maximal electroshock seizure model. Results indicate that MRZ 2/576 administered intraperitoneally, 5 min before the test, exerted a clear-cut anticonvulsant effect in the maximal electroshock seizure test in mice and its ED(50) value was 13.71 (11.95-15.73) mg/kg. In the subthreshold method, MRZ 2/576 (administered intraperitoneally, at a subthreshold dose of 5 mg/kg) significantly enhanced the anticonvulsant action of felbamate, oxcarbazepine and topiramate, by reducing their ED(50) values from 73.0 to 53.8 mg/kg (p < 0.05) for felbamate, from 10.77 to 7.48 mg/kg (p < 0.05) for oxcarbazepine, and from 49.3 to 28.7 mg/kg (p < 0.01) for topiramate. In contrast, MRZ 2/576 (5 mg/kg, i.p.) did not significantly affect the antiseizure effects of lamotrigine in the maximal electroshock seizure test in mice. Isobolographic transformation of data revealed that MRZ 2/576 (5 mg/kg, i.p.) exerted barely additive interactions with all investigated antiepileptic drugs in the maximal electroshock seizure test. In conclusion, the isobolographic analysis revealed that MRZ 2/576 additively cooperates with newer antiepileptic drugs in terms of suppression of maximal electroshock-induced seizures in mice.

Isobolographic characterization of interactions between vigabatrin and tiagabine in two experimental models of epilepsy

To characterize the type of interactions between vigabatrin (VGB) and tiagabine (TGB) -- two newer antiepileptic drugs influencing GABA-ergic neurotransmitter system, the isobolographic analysis was used in two experimental models of epilepsy: the maximal electroshock seizure threshold (MEST) test and pentylenetetrazole (PTZ)-induced seizures in mice. Results indicated that VGB and TGB administered separately (i.p.) increased the electroconvulsive threshold in mice, which allowed the calculation of their TID(20) values (threshold increasing doses by 20% over the threshold of control animals) in the MEST test. The TID(20) for VGB was 226.2 mg/kg and that for TGB was 4.4 mg/kg. With isobolography, the combinations of VGB with TGB (at fixed-ratios of 1:3, 1:1 and 3:1) exerted additive interactions in the MEST test in mice. Similarly, VGB and TGB injected separately (i.p.) suppressed the PTZ-induced seizures, and their ED(50) values (median effective doses, protecting 50% of the animals tested against clonic convulsions) for VGB and TGB were 622.5 mg/kg and 0.8 mg/kg, respectively. Isobolographic analysis of interactions revealed that the combinations of VGB with TGB at the fixed-ratios of 1:3 and 1:1 produced supra-additive (synergistic) interactions against PTZ-induced seizures. Only the combination of VGB with TGB at the fixed-ratio of 3:1 was additive in the PTZ test. The evaluation of acute adverse-effect potential for all fixed-ratio combinations of VGB with TGB (administered at their TID(20) and ED(50) values from the MEST and PTZ tests) revealed that none of the examined combinations affected motor coordination in the chimney test and altered neuromuscular tone in the grip-strength test in mice. In contrast, VGB in combinations with TGB produced the antinociceptive effects with respect to suppression of acute thermal pain in animals subjected to the hot-plate test. Based on this preclinical study, one can ascertain that the combination of VGB with TGB would provide an adequate seizure control in epileptic patients.

Isobolographic analysis of interaction between drugs with nonparallel dose-response relationship curves: a practical application

The objective of this study was to characterize the anticonvulsant and acute adverse-effect potentials of topiramate (TPM) and gabapentin (GBP)-two second-generation antiepileptic drugs administered alone and in combination in the maximal electroshock (MES)-induced seizures and chimney test in mice. The anticonvulsant and acute adverse effects of the combination of TPM with GBP at the fixed ratio of 1:1 were determined using the type I isobolographic analysis for nonparallel dose-response relationship curves (DRRCs). To ascertain any pharmacokinetic contribution to the observed interaction between TPM and GBP, total brain concentrations of both drugs were determined. The isobolographic analysis of interaction for TPM and GBP, whose DRRCs were not parallel in both MES and chimney tests, was accompanied with a presentation of all required calculations allowing the determination of lower and upper lines of additivity. The isobolographic analysis revealed that TPM combined with GBP at the fixed-ratio combination of 1:1 interacted supraadditively (synergistically) in terms of suppression of MES-induced seizures, and simultaneously, the combination produced additive interaction with respect to motor coordination impairment (adverse effects) in the chimney test. The evaluation of pharmacokinetic characteristics of interaction for the combination of TPM with GBP revealed that neither TPM nor GBP affected their total brain concentrations in experimental animals, and thus, the observed interaction in the MES test was pharmacodynamic in nature. In conclusion, the combination of TPM with GBP, because of supraadditivity in the MES test and additivity in terms of motor coordination impairment in the chimney test as well as lack of pharmacokinetic interactions between drugs, fulfilled the criterion of a favorable combination, worthy of recommendation in further clinical practice.

Improvement in seizure control and quality of life in medically refractory epilepsy patients converted from polypharmacy to monotherapy

In a retrospective chart review, we identified 35 patients with medically refractory epilepsy (MRE) who had been converted from polypharmacy to monotherapy and maintained on monotherapy for at least 12 months. None of the 35 patients had worsening of their seizure frequency after the conversion to monotherapy. Fourteen of the 35 patients (40%) became seizure-free. Nine of 35 patients (26%) had a 50% reduction in seizure frequency. Five of 35 patients (14%) had a 75% reduction in seizure frequency. Twenty-eight (80%) of 35 patients participated in a quality-of-life questionnaire. Quality of life was rated as better on monotherapy as compared with polypharmacy in a number of domains: memory loss, concern over medication long-term effects, difficulty in taking the medications, trouble with leisure time activities, and overall state of health. This improvement reached statistical significance. Conversion to monotherapy in patients with MRE may be successful in achieving a reduction in seizure frequency and an improvement in quality-of-life parameters. A prospective, randomized trial is necessary to validate these findings.

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.

Future prospects for the drug treatment of epilepsy

Great progress has been made in the last 150 years in the pharmacological management of epilepsy, and, despite the increasing number of technological advances available, antiepileptic drugs (AEDs) remain the mainstay of treatment for the vast majority of patients with epilepsy. This review looks at possible avenues of development in the drug treatment of epilepsy. The strengths and weaknesses of those AEDs which are currently licensed are examined, and ways in which their use may be improved are discussed (e.g. rational combinations, use of new formulations). Potentially new targets that may allow the development of effective treatments are highlighted (neuroimmunological manipulation, decreasing inherent drug resistance mechanisms, and modification of adenosine neurotransmission), and a summary of the most promising AEDs currently in development is provided [e.g. carabersat, ganaxolone, harkoseride, MDL 27192, safinamide (NW 1015), pregabalin, retigabine, talampanel, valrocemide, losigamone and BIA 2093].