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Pharmacokinetics of Ondansetron in Pregnant Women and Neonates
Abstract Number: BP-03
Abstract Type: Original Research
Introduction: Ondansetron is a potent, selective 5-HT3 antagonist used to prevent and treat nausea and vomiting in obstetrics.(1) Ondansetron may also be effective in preventing maternal narcotic withdrawal symptoms or neonatal abstinence syndrome (NAS).(2) Physiological changes in pregnancy may affect drug pharmacokinetics (PK), however there is limited information about ondansetron PK in pregnant women or neonates. The aim of this study was to characterize ondansetron PK in pregnant (versus non-pregnant) women and neonates, and determine placental transfer.
Methods: Healthy women undergoing cesarean delivery were randomly assigned to receive 4- or 8-mg IV ondansetron for this prospective, open-label, IRB-approved study. A population PK approach was used to analyze ondansetron concentrations in 372 blood samples obtained from 20 non-pregnant and 40 pregnant women and their neonates after treatment with either 4- or 8-mg of ondansetron. Maternal blood was sampled at 7, 15, 40 min, and 8 h after ondansetron administration; neonatal levels were measured at 30 and 90 min, 2, 6 and 24 h after birth; and ondansteron levels were measured from venous umbilical cord blood at time of delivery. A two-compartment linear disposition model was used to describe the data and a two-stage NONMEM approach applied to obtain covariate modeling. Visual predictive check evaluated final model prediction of observed and predicted ondansetron concentrations.
Results: The analysis demonstrated that ondansetron PK is not affected by pregnancy; the ondansetron dose was the most important covariate affecting its PK; ondansetron readily crossed the placenta; and ondansetron displayed a significantly longer half-life in neonates (Figure). The mean population parameter estimates were central distribution volume of 28 L; clearances of 22 L/h and 15 L/h for 4- and 8-mg doses respectively; and steady-state volumes of 167 L and 124 L for 4- and 8-mg doses respectively.
Conclusions: Ondansetron exhibits pregnancy-independent PK suggesting that the dose does not need to be altered during pregnancy. Ondansetron readily crosses the placenta, and neonatal drug elimination during the first day of life is significantly delayed compared to maternal elimination. Data from this study can be used to guide trans-placental and neonatal dosing regimens to prevent NAS in babies born to narcotic-consuming mothers.
1. Anesth Analg 2009; 109:174-82
2. Pharmacogenetics and Genomics 2009; 19:1