Alfentanil pharmacokinetics in patients undergoing abdominal aortic surgery

The pharmacokinetics of alfentanil, 300 micrograms.kg-1 IV, were determined in patients undergoing elective abdominal aortic reconstruction. The mean age (+/- SD) of the patients was 64.3 +/- 7.4 yr; their mean weight was 74.7 +/- 13.8 kg. Five patients underwent aneurysm repair and six had aortobifemoral grafting. Serum alfentanil concentrations were measured by gas-liquid chromatography in samples drawn at increasing intervals over a 24-hr period. A three-compartment model was fitted to the concentration versus time data. The volume of the central compartment and the volume of distribution at steady state (Vdss) were 0.44 +/- 0.022 and 0.63 +/- 0.32 L.kg-1, respectively. Total drug clearance was 6.4 = 1.9 ml.min-1.kg-1. The elimination half-time was 3.7 +/- 2.6 hr. Patient age was positively correlated with both Vdss and elimination half-time. There were no significant correlations between the pharmacokinetic variables and the duration of aortic cross-clamping, the duration of surgery, or the rate or total volume of IV fluids infused intraoperatively. In general surgical patients, the elimination half-time of alfentanil has been reported to be 1.2-2.0 hr. Although the elimination half-time of alfentanil was longer in patients undergoing abdominal aortic surgery, alfentanil was eliminated much faster than either fentanyl or sufentanil in this patient population.