The effects of cimetidine chronic treatment on conventional antiepileptic drugs in mice.

PURPOSE: The aim of this study was to evaluate the effects of 1-day, 7-day and 14-day administrations of cimetidine on the anticonvulsant activity of conventional antiepileptic drugs (AEDs; valproate, carbamazepine, phenytoin and phenobarbital) against maximal electroshock (MES)-induced convulsions in mice. METHODS: Electroconvulsions were evoked in Albino Swiss mice by a current delivered via ear-clip electrodes. In addition, the effects of cimetidine, AEDs alone and their combinations were studied on performance and long-term memory tests. Pharmacokinetic changes in plasma and brain concentrations of AEDs after cimetidine administration were evaluated with immunofluorescence. RESULTS: Cimetidine (up to 100mg/kg) after 1-day administration did not affect the electroconvulsive threshold in animals. Moreover, in the 14-day treatment, cimetidine administered at a dose of 40mg/kg did not significantly change the electroconvulsive threshold in the MES-test, cimetidine administered 14-day (at 20mg/kg) significantly increased the anticonvulsant activity of carbamazepine, staying without effects after a 1-day and 7-day studies. In contrast, both the 7-day and 14-day administrations of cimetidine resulted in significant reductions of protective efficacy of the phenobarbital. Only valproate and phenytoin were not affected by cimetidine (20mg/kg) in all experimental period. Cimetidine administered 1-day, did not alter total brain concentrations and free plasma levels of all AEDs tested, whilst the 14-day study elevated carbamazepine plasma and brain concentration and reduced phenobarbital brain concentration. Cimetidine co-applied with AEDs did not impair performance of mice evaluated in the chimney test however, it worsened long-term memory in animals. CONCLUSIONS: Based on this preclinical study, a special caution is advised when treating epileptic patients with combinations of phenobarbital or carbamazepine with cimetidine.