Interactions between two enantiomers of losigamone and conventional antiepileptic drugs in the mouse maximal electroshock model--an isobolographic analysis

The aim of this study was the isobolographic evaluation of interactions between two enantiomers of losigamone, AO-242 (+)-5(R)-alpha(S)-5-(2-chlorophenylhydroxymethyl)-4-methoxy-2(5H)-furanone] and AO-294 (-)-5(S)-alpha(R)-5-(2-chlorophenylhydroxymethyl)-4-methoxy-2(5H)-furanone], and valproate, carbamazepine, phenytoin, or phenobarbital in the maximal electroshock test in mice. Both enantiomers interacted additively with conventional antiepileptic drugs at all studied fixed dose ratios (1:3, 1:1, 3:1). Furthermore, AO-242, AO-294 and antiepileptics applied alone, as well as combinations of enantiomers and antiepileptics did not affect motor performance in the chimney test. Significant impairment of long-term memory (passive-avoidance task) was noted only in the case of valproate alone, given at the dose equal to its median effective dose (ED(50)) against maximal electroshock. All other antiepileptics and their combinations with AO-242 or AO-294 did not impair memory of mice. Enantiomers did not affect the brain concentrations of antiepileptic drugs, indicating a pharmacodynamic nature of the observed interactions. In conclusion, the present results suggest both AO-242 and AO-294 as promising candidate drugs in the add-on therapy of refractory epilepsy.