Oxytocin is the first-line drug to promote contraction of the uterus and prevent atony
immediately after delivery. Nonetheless, unpredictable uterine atony refractory to oxytocin
affects roughly 250,000 parturients annually in the U.S. and rates are increasing. This
two-part study will measure the action of oxytocin at cesarean delivery. The first part will
measure the pharmacokinetics (or 'what the body does to the drug') of a single intravenous
(IV) dose of deuterium-labeled oxytocin (a novel tracing method to distinguish this dose from
pre-existing oxytocin in the body and the standard variable dosing given in cesarean
delivery). The second part will measure the pharmacodynamics (or 'what the drug does to the
body') of all plasma oxytocin to see how concentrations correspond to the contractile effect
on the uterus.
After delivery of the fetus, study subjects will receive a bolus of IV deuterated oxytocin
followed by an unlabeled oxytocin infusion. Venous blood samples drawn at multiple time
points (within 1 hour after delivery) will be analyzed for plasma concentrations of labeled
and unlabeled (endogenous + exogenous infused) oxytocin over time. Plasma concentrations will
be compared with 0-10 uterine tone scores measuring uterine contraction strength, to describe
the concentration-effect relationship.
The goal of this study is to define both the pharmacokinetics and pharmacodynamics of
oxytocin in parturients to help identify the cause(s) of failed first-line oxytocin therapy.