Niguldipine impairs the protective activity of carbamazepine and phenobarbital in amygdala-kindled seizures in rats.

There is evidence that some calcium (Ca(2+)) channel inhibitors enhance the protective activity of antiepileptic drugs. Since clinical trials have not provided consistent data on this issue, the objective of this study was to evaluate the interaction of a dihydropyridine, niguldipine, with conventional antiepileptics in amygdala-kindled rats. Niguldipine (at 7.5 but not at 5 mg/kg) displayed a significant anticonvulsant effect, as regards seizure and afterdischarge durations in amygdala-kindled convulsions in rats, a model of complex partial seizures. No protective effect was observed when niguldipine (5 mg/kg) was combined with antiepileptics at subeffective doses, i.e. valproate (75 mg/kg), diphenylhydantoin (40 mg/kg), or clonazepam (0.003 mg/kg). Unexpectedly, the combined treatment of niguldipine (5 mg/kg) with carbamazepine (20 mg/kg) or phenobarbital (20 mg/kg) resulted in a proconvulsive action. BAY k-8644 (an L-type Ca(2+) channel activator) did not modify the protective activity of niguldipine (7.5 mg/kg) or the opposite action of this dihydropyridine (5 mg/kg) in combinations with carbamazepine or phenobarbital. A pharmacokinetic interaction is not probable since niguldipine did not affect the free plasma levels of the antiepileptics. These data indicate that the opposite actions of niguldipine alone or combined with carbamazepine (or phenobarbital) were not associated with Ca(2+) channel blockade. The present results may argue against the use of niguldipine as an adjuvant antiepileptic or for cardiovascular reasons in patients with complex partial seizures.