Pharmacodynamic interaction of eltanolone and alfentanil during lower abdominal surgery in female patients.

We have studied the influence of eltanolone on intraoperative alfentanil requirements in 18 female patients undergoing lower abdominal surgery receiving target-controlled infusions of eltanolone and alfentanil. While target concentrations of eltanolone were maintained constant, target concentrations of alfentanil changed in response to the presence or absence of responses. With serum eltanolone concentrations increasing from 500 to 2000 ng ml-1, the EC50 of alfentanil for suppression of responses to surgical stimulation decreased from 233 to 9 ng ml-1. The findings suggest that the interaction between eltanolone and alfentanil is synergistic.