Objective Adequate data on fentanyl pharmacokinetics in neonates are lacking. The study was performed to compare serum concentrations and clinical outcome between continuous infusion (CI) and intermittent bolus (IB) doses of fentanyl for analgesia and sedation in neonates.

Methods In this open-label randomised controlled trial, neonates requiring 24–48 hours of mechanical ventilation and fentanyl administration were recruited. In CI regimen, 1 mcg/kg loading dose was followed by 1 mcg/kg/hour infusion. In IB regimen, 1mcg/kg/dose was administered every 4 hours.

Maximum six blood samples were collected in 48 hours from each baby at prespecified time points for estimating serum fentanyl concentration. Secondary outcomes were pain scores (Neonatal Infant Pain Scale and Neonatal Pain, Agitation and Sedation Scale for acute and ongoing pain, respectively) and incidence of adverse effects of fentanyl.

Results 100 neonates were recruited, 53 in CI and 47 in IB group. In CI regimen, median (IQR) serum fentanyl concentration was 0.42 (0.35, 0.46) to 0.61 (0.47, 0.89) ng/mL throughout the infusion period. In IB regimen, median (IQR) peak concentration ranged from 2.21 (1.82, 3.55) to 3.61 (2.91, 4.51) ng/mL and trough concentration 0.41 (0.33, 0.48) to 0.97 (0.56, 1.25) ng/mL for various doses.

Median (IQR) peak concentration (C_max, 3.06 (1.09, 4.50) vs 0.78 (0.49, 1.73) ng/mL; p<0.001) was significantly higher and area under concentration-time curve (AUC_0–24, 19.6 (10.4, 33.5) vs 13.2 (10.8, 22.6) µg·hour/L; p=0.12) was higher (though not statistically significant) in IB than CI regimen. Pain scores and adverse effects were comparable between the two regimens.

Conclusion CI regimen of fentanyl produces steady serum concentrations, whereas IB regimen produces wide fluctuations in serum concentration with high-peak concentrations. A serum fentanyl concentration of 0.4–0.6 ng/mL produces adequate analgesia and sedation in neonates.

Trial registration number CTRI/2014/11/005190.