IT INHIBITS LIVER METABOLISM OF BENZODIAZEPINES, BETA-BLOCKERS, CARBAMAZEPINE, ANTIDEPRESSANTS, PHENYTOIN AND WARFARIN, SO REDUCE THEIR DOSES TO 1/3. DECRESSED EFFICACY IN HEAVY SMOKERS. INCREASED RISK OF RESPIRATORY DEPRESSION, AND HYPOTENSION WITH HALOTHANE. INCREASED ANTICOAGULANT EFFECT. RESPIRATORY DEPRESSANT EFFECT ENHANCED BY LIDOCAINE. ACTION POTENTIATED BY ALCOHOL, CNS DEPRESSANTS,BENZODIAZEPINES. INCOMPATIBLE WITH SOLUBLE BARTITURATES. PLASMA CONCENTRATIONS OF DEXTROPROPOXYPHENE ARE INCREASED BY RITONAVIR