Placental transfer of ondansetron during early human pregnancy.

BACKGROUND AND OBJECTIVE Nausea and vomiting are common conditions that occur during early pregnancy and can be disabling. Ondansetron had been used in pregnant women when treatment with conventional antiemetics has failed; however, the safety and tolerability of this relatively new antiemetic drug during pregnancy is still uncertain. The objective of this study was to quantify the placental transfer of ondansetron in the first trimester of human pregnancy. PATIENTS AND METHODS This was a prospective, observational study. Forty-one patients who requested surgical termination of pregnancy at the first trimester were administered three doses of ondansetron 8 mg before surgery. Maternal venous blood, coelomic fluid, amniotic fluid and fetal tissue were collected from each patient for analysis of ondansetron by liquid chromatography-mass spectometry. RESULTS Ondansetron was found in all samples. Drug concentration in fetal tissue was significantly higher than that in the amniotic fluid and similar to that in the coelomic fluid. The median (interquartile range) fetal/maternal ratio was 0.41 (0.31-0.52) and there were no significant correlations between ondansetron concentrations in each compartment and gestational age. CONCLUSIONS A significant amount of ondansetron was present in all embryonic compartments. The developmental significance of this drug exposure requires further investigation, i.e. whole embryo culture.