Antagonism of the convulsant effects of heroin, d-propoxyphene, meperidine, normeperidine and thebaine by naloxone in mice.

Naloxone antagonized convulsions produced by tail vein infusions of d-propoxyphene, heroin, meperidine, normeperidine and thebaine in mice in a dose-related manner. Pretreatment with naloxone (60 mg/kg i.p.) produced a 200 percent increase of the dose of d-propoxyphene or heroin needed to produce a seizure. A 40 percent increase in the convulsant dose of meperidine was observed after naloxone pretreatment (30 mg/kg i.p.). Naloxone (15 mg/kg i.p.) produced a 30 percent increase in the convulsant dose of normeperidine; however, larger doses of naloxone did not produce any further increase in the convulsant dose of either normeperidine or meperidine. Larger doses of naloxone were needed to antagonize convulsions produced by thebaine. Heroin, d-propoxyphene and meperidine produced nonlethal clonic seizures, whereas normeperidine and thebaine produced tonic-clonic seizures which were followed by death. These data suggest that there may be two mechanisms by which narcotic analgesics and their congeners produce convulsions.