A study of the interaction of nalorphine with fentanyl and innovar

Abstract The lower segment of the biphasic mortality dose response curve of fentanyl citrate appears to be due to respiratory depression and is readily antagonized by nalorphine. The analgesic activity of fentanyl citrate and of Innovar ® is also antagonized by nalorphine, as is the case with morphine. In order to raise the analgesic ED 50 of Innovar in terms of its content of fentanyl citrate to four times the ED 50 of fentanyl citrate alone, four times as much nalorphine was required as was needed to elevate the ED 50 of fentanyl citrate fourfold. The amount of nalorphine necessary to elevate significantly the LD 50 of Innovar was six times greater than that needed with fentanyl citrate. Addition of nalorphine toxicity with that of fentanyl citrate and of Innovar, respectively, occurs when lethal doses of nalorphine are used. In dogs, nalorphine effectively antagonizes the cardiovascular effects of fentanyl citrate.