Gestational age and birth weight effects on plasma clearance of fentanyl in newborn infants.

OBJECTIVE

To provide a rational basis for the dosage of fentanyl in newborn infants by determining clearance in the first days of life.

STUDY DESIGN

A continuous infusion of fentanyl for 2 to 3 days (10. 5 microg/kg over a 1-hour period followed by 1.5 microg/kg/h) was administered to 38 newborn infants who had undergone ventilation (gestational ages 26 to 42 weeks and birth weights 835 to 3550 g). Fentanyl concentrations were measured in arterial blood samples collected at 2, 12, 24, 48, and 60 hours after the start of fentanyl infusion. Fentanyl levels were correlated with a pain score.

RESULTS

The mean (+/-SD) steady-state fentanyl concentration of 2.5 (+/-1) ng/mL achieved between 24 and 48 hours of infusion correlated significantly with the concomitant pain score (r = -0.57, P <.01). The clearance, 11.5 (+/-4.0) mL/min/kg, correlated significantly with the gestational age (r = 0.46, P <.01) and birth weight (r = 0. 48, P <.01).

CONCLUSIONS

Because plasma fentanyl clearance increases with maturity, gestational age should be taken into account when fentanyl is administered to newborn infants.