Abstract
Fentanyl citrate, a potent short activity narcotic is being considered for obstetrical analgesia/anesthesia. Fentanyl is highly protein bound (67%) and very lipid soluble (N-haptane 22), the latter suggesting rapid placental transfer of the unbound drug. We evaluated the kinetics and placental transfer of Fentanyl in 5 chronically catheterized pregnant ewes (near term) and their fetuses following intravenous injection of Fentanyl (4 μg/kg). Fentanyl was measured in serial blood samples from maternal arterial (MA) blood and fetal umbilical arterial (UA) and venous blood (UV) by radioimmunoassay. Similar kinetic studies were performed in 5 newborn lambs.
Preliminary analysis of Fentanyl concentrations in MA blood indicate a tri-compartmental washout with a rapid αt½ (2-4 min) and a slow γt½ (hrs). Newborn lambs exhibited similar kinetics. Fentanyl was present in UV blood for 5-10 min following maternal injection, but only at UV/MA ratios of less than 0.16, and it was usually not detectable in fetal arterial blood. No changes in maternal or fetal heart rate, blood pressure, or blood gases occurred during Fentanyl administration.
Our data indicate that Fentanyl levels in fetal sheep, following maternal administration of dosages that would be analgesic for humans, should be insignificant. Fentanyl appears to have significant potential for obstetrical usage.
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Eisele, J., Goetzman, B., Milstein, J. et al. 323 PLACENTAL TRANSFER OF FENTANYL IN SHEEP. Pediatr Res 15 (Suppl 4), 494 (1981). https://doi.org/10.1203/00006450-198104001-00334
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DOI: https://doi.org/10.1203/00006450-198104001-00334