Interactions between morphine-like analgesics and anticonvulsant drugs.

The effect of pretreatment with morphine-like analgesics on the anticonvulsant effect of phenytoin and phenobarbital against electroconvulsions and of phenobarbital and ethosuximide against pentetrazole-induced convulsions was studied in mice. High doses of morphine (4 mg/kg subcutaneously), fentanyl (100 micrograms/kg subcutaneously), pethidine and pentazocine (4 and 8 mg/kg subcutaneously) increased the anti-electroshock effect of phenytoin; that of phenobarbital was likewise increased by morphine (2 and 4 mg/kg), fentanyl (25-100 micrograms/kg) and pentazocine (2-8 mg/kg), whereas pethidine had no corresponding effect. There was no consistent effect of pretreatment with the analgesics studied on the anticonvulsant effects of phenobarbital and ethosuximide in the pentetrazole seizure threshold test.