Pharmacokinetics of fentanyl administered via peridural route in the woman in labor

Seven women in labour received a single epidural dose of 0.8 mcg/kg of fentanyl together with bupivacaine. A pharmacokinetic study was performed of the fentanyl. As previously described, plasma concentrations were low. However, wide variations and important fluctuations were observed between different individuals with frequent late second peaks. The explanation for these second peaks of plasma fentanyl is discussed. The dose of fentanyl used in epidural administration for pain relief in labour must not be over 1 mcg/kg in order to avoid toxic levels, in the fetus.