Interaction of diazepam with meperidine or normeperidine on analgesia and lethality.

The effects of meperidine and normeperidine were determined alone and after pretreatment with 10 mg/kg of diazepam on the tail-withdrawal measure of analgesia in rats. Lethal doses of normeperidine were determined alone and in combination with three doses of diazepam, and lethal doses of meperidine were determined along and in combination with 10 mg/kg of diazepam. Diazepam potentiated the analgesic effects of meperidine and increased the dose of normeperidine necessary to produce lethality.