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 aim of this study was to assess the influence of agmatine (an endogenous neuromodulator/neurotransmitter in the brain) on the protective action of numerous classical and second-generation antiepileptic drugs (clonazepam, ethosuximide, gabapentin, phenobarbital, tiagabine, vigabatrin, and valproate) in the mouse pentetrazole-induced clonic seizure model. The results indicate that agmatine (up to 100 mg/kg, ip, 45 min before the test) did not alter the threshold for pentetrazole-induced clonic seizures in mice. However, agmatine (100 mg/kg, ip) significantly attenuated the anticonvulsant effects of vigabatrin against pentetrazole-induced clonic seizures by elevating the ED(50) value of vigabatrin from 517.5 to 790.3 mg/kg (p < 0.01). In contrast, agmatine at a dose of 50 mg/kg did not significantly affect the anticonvulsant action of vigabatrin, although an increase in the ED(50) value of the antiepileptic drug from 517.5 to 629.1 mg/kg was documented. Moreover, agmatine at doses of 50 and 100 mg/kg (ip) had no significant impact on the anticonvulsant action of clonazepam, ethosuximide, gabapentin, phenobarbital, tiagabine, or valproate in pentetrazole-induced seizures in mice. In conclusion, the combination of agmatine with vigabatrin seems to be unfavorable due to the reduction of the anticonvulsant effect of vigabatrin after concomitant administration of agmatine in the pentetrazole-induced seizure model. Therefore, the utmost caution is advised when combining agmatine with vigabatrin in further clinical settings.