Plasma concentrations of alfentanil following epidural administration

The plasma concentration-time profile of alfentanil following epidural administration was determined in eight patients undergoing lower abdominal surgery under nitrous oxide (66%)-oxygen (33%)-halothane (0.3%) anaesthesia, supplemented with intravenous sufentanil. Alfentanil (1 mg) was administered epidurally before induction of general anaesthesia. Blood samples for the determination of plasma alfentanil concentrations by capillary gas chromatography were collected at intervals until 12 h after the epidural injection. Peak plasma concentrations [mean (SD)] were 9.7 (2.3)ng.ml-1, and were attained in a median (range) time of 90 (30-120) min. The results suggest that alfentanil is slowly absorbed from the epidural space into the general circulation.