Propofol and fentanyl act additively for induction of anaesthesia.

The induction dose-response of propofol was compared with the dose-response of its combination with fentanyl and with that of fentanyl alone in three groups of 60 women undergoing minor gynaecological surgery. Dose-response curves were determined for each group using bootstrap and isobolographic analyses. Propofol was found to act additively with fentanyl for induction of anaesthesia. Twenty-three percent of the ED50 of fentanyl was required in combination with 75% of the ED50 for propofol to achieve the ED50 of the combination. This indicates that, for induction of anaesthesia, propofol and fentanyl are not synergistic.