OPIOIDS AND PHENOBARBITAL - FENTANYL, METHADONE OR PETHIDINE (MEPERIDINE)

Phenobarbital and primidone appear to increase fentanyl and methadone require- ments. Methadone withdrawal reactions have been seen. The analgesic effects of pethidine can be reduced by barbiturates.
Monitor concurrent use to ensure the opioid effects are adequate.