The sedative effect of benzodiazepines and opiods is potentiated by other CNS depressants including alcohol, barbiturates, inhaled and injected anesthetics, and opioids.
Anesthetic requirements for inhaled and injected anesthetics are decreased by benzodiazepines and opiods . Benzodiazepines decrease the MAC value of inhaled anesthetics.
Benzodiazepines, especially midazolam, potentiate the ventilatory depressant effects of opioids, though the analgesic property is reduced.
Cimetidine inhibits the metabolism of diazepam and thus prolongs its action. Erythromycin inhibits the action of midazolam.
The combination of benzodiazepines and opiods has thus a increased accumulated and synergistical action of both these drugs, especially with regards to its sedative and respiratory depressive effects.