[Comparison between the analgesic effects of fentanyl and morphine in conscious man (author's transl)].

Fentanyl citrate is administered intramuscularly at increasing doses to patients suffering from an intense pain in the facial or trigeminal nerves territory. Fentanyl induces a very intense analgesia which develops during the hour following the administration. The intensity and the duration of the effect are dose related. Compared to that of morphine chlorhydrate, in the same conditions, the analgesia induced by fentanyl citrate is much less intense than expected: fentanyl seems to be only 25 times more potent than morphine. Furthermore, the observed duration of action of fentanyl makes it impossible to be still classified with the short time acting analgesics: with equianalgesic doses, morphine and fentanyl have the same time of initiation and the same duration of action. As observed, the time of the clinically useful analgesia is longer than 3 hours after injection of 0.006 mg/kg of fentanyl or of 0.150 mg/kg of morphine.