Plasma and colostrum concentrations of fentanyl in clinical practice: Intravenous versus epidural administration for labor analgesia

INTRODUCTION: Pain relief during labor is essential. Systemic opioids for labor analgesia have been used for decades as a less invasive alternative to epidural analgesia (EA). Although their analgesic efficacy is generally considered inferior to EA, concerns regarding potential maternal and neonatal adverse effects have likely limited their wider adoption. Measurements of fentanyl concentration may provide an objective assessment of systemic exposure and potential transfer to the fetus and colostrum. The aim of the study was to compare fentanyl concentrations in maternal plasma, umbilical cord blood, and colostrum following intravenous (midwife-administered) versus epidural administration for labor analgesia. We also included a group of women, who initially received intravenous fentanyl but were subsequently converted to EA due to insufficient pain relief. MATERIAL AND METHODS: This prospective study included three groups: women who received fentanyl epidurally only (EA), intravenously only (IV), or intravenously followed by epidural administration (IV + EA). Samples of maternal plasma, arterial and venous umbilical cord plasma, and two colostrum samples were collected for analysis of fentanyl concentration. RESULTS: A total of 98 women were included: 34 in the EA group, 38 in the IV group and 26 in the IV + EA group. Fentanyl concentrations were significantly higher in the IV group compared to the EA group in maternal plasma (0.25 ng/mL vs. 0.11 ng/mL, p < 0.001) and umbilical vein plasma (0.084 ng/mL vs. 0.054 ng/mL, p < 0.001). However, within the first 24 h postpartum, no significant differences in fentanyl concentrations were observed in colostrum samples between the IV and EA groups (0.020 ng/mL vs. 0.021 ng/mL, p = 0.93). The estimated theoretical infant dose through breastfeeding in the total study population was very low (0.0079 μg). All measured fentanyl concentrations were low and were accompanied by normal early warning scores, with no requirement for naloxone administration or ventilator support in any group. CONCLUSIONS: Intravenous fentanyl for labor analgesia was associated with low fentanyl concentrations in maternal plasma, umbilical cord plasma, and colostrum. These findings suggest that intravenous fentanyl may be considered as an additional analgesic option for laboring women.