Abstracts

Rationale: Amygdala kindling is a reputed epilepsy model in rodents mimicking complex partial seizures with secondary generalization in man. It has also been proposed as a model of drug-resistant epilepsy, particularly in animals not responding to phenytoin. In the present study we decided to use fully amygdala-kindled mice to compare the anticonvulsant efficacy of levetiracetam (Keppra^®) and brivaracetam, a novel high-affinity synaptic vesicle protein 2A (SV2A) ligand displaying inhibitory activity at neuronal voltage-dependent sodium channels, which is currently in Phase III development for epilepsy. Methods: Male C57BL/6 mice were implanted with a bipolar electrode in the amygdala. Kindling was performed by once daily supra-threshold stimulations with 1 sec. monophasic current trains (1 ms single pulse duration, frequency 50 Hz and 250 µA intensity). The behavioral effect of stimulation was scored according to Racine’s scale where 0 = no reaction, 1 = facial twitches and chewing, 2 = head nodding, 3 = forelimb clonus, 4 = forelimb clonus with rearing and 5 = generalized clonic convulsions associated with loss of balance. All compounds were injected i.p. in fully-kindled mice at different doses and pretreatment times: brivaracetam (6.8-210 mg/kg; 30 min), levetiracetam (17-540 mg/kg; 60 min) and phenytoin (10-70 mg/kg; 120 min). Results: Brivaracetam produced dose-dependent protection against generalized seizures (score ≥ 3) with an ED₅₀ value of 68.3 (39.3-118.6) mg/kg. Although levetiracetam also had dose-dependent effects, it was not possible to calculate its ED₅₀ value because only 60% of the animals were protected by the highest dose tested. Phenytoin (up to 70 mg/kg) was ineffective and no mice were protected against generalized seizures. Pretreatment with the highest doses afforded different degree of efficacy expressed as the maximal reduction of the mean seizure score: brivaracetam (90%), levetiracetam (40%) and phenytoin (12%). It is noteworthy that complete protection against kindled seizures (score 0) was observed in 70% of the animals treated with the highest dose of brivaracetam, while none of the mice was fully protected after pretreatment with maximal doses of levetiracetam and phenytoin. Brivaracetam (210 mg/kg) markedly decreased the afterdischarge duration (84.5%), while the effects of levetiracetam (540 mg/kg) and phenytoin (70 mg/kg) on this parameter were less pronounced, 36.4% and 19.6% respectively. Conclusions: The present results demonstrate that brivaracetam displays significant protection against both partial and generalized seizures in fully amygdala-kindled mice, which were resistant to phenytoin. The effects of levetiracetam appeared limited as it was only partially effective and less potent than brivaracetam. The superior activity of brivaracetam compared to both levetiracetam and phenytoin in this preclinical model highlights a promising treatment potential in drug-resistant epilepsy.