PETHIDINE AND RELATED DRUGS ARE CONTRA-INDICATED IN PATIENTS TAKING MAOIS OR WITHIN 14 DAYS OF STOPPING SUCH TREATMENT;SELEGILINE, A SELECTIVE INHIBITOR OF MONOAMINE OXIDASE TYPE B, HAS BEEN GIVEN WITH SERIOUS LIFE THREATENING COMPLICATIONS. THE DEPRESSANT EFFECTS OF OPIOID ANALGESICS ARE ENHANCED BY OTHER CNS DEPRESSANTS SUCH AS ALCOHOL, ANAESTHETICS, ANXIOLYTICS, HYPNOTICS, TRICYCLIC ANTIDEPRESSANTS, AND ANTIPSYCHOTICS. CYCLIZINE MAY COUNTERACT THE HAEMODYNAMIC BENEFITS OF OPIOIDS. CIMETIDINE INHIBITS THE METABOLISM OF SOME OPIOIDS, ESPECIALLY PETHIDINE.
THE ACTIONS OF OPIOIDS MAY IN TURN AFFECT THE ACTIVITIES OF OTHER DRUGS. FOR INSTANCE, THEIR GASTROINTESTINAL EFFECTS MAY DELAY ABSORPTION AS WITH MEXILETINE OR MAY BE COUNTERACTIVE AS WITH CISAPRIDE, METOCLOPRAMIDE, OR DOMPERIDONE. OPIOID PREMEDICANTS SUCH AS PAPAVERETUM HAVE BEEN REPORTED TO REDUCE SERUM CONCENTRATIONS OF CIPROFLOXACIN.