Pharmacology and placental transport of 17-hydroxyprogesterone caproate in singleton gestation.

OBJECTIVE: The purpose of this study was to estimate pharmacokinetic parameters and to evaluate placental transport of 17-hydroxyprogesterone caproate (17-OHPC) in singleton gestation. STUDY DESIGN: Sixty-one women who received weekly injections of 17-OHPC underwent 2 pharmacokinetic studies at 20 + 0 to 24 + 6 weeks' gestation (study 1) and 31 + 0 to 34 + 6 weeks' gestation (study 2); daily blood samples were obtained between injections. In 18 women, blood samples were obtained over a 28-day period beyond the last injection (extended study). Maternal and/or cord blood were obtained at delivery. RESULTS: The half-life (median ± SD) of 17-OHPC was 16.2 ± 6 days. Concentrations of 17-OHPC were higher during study 2 than during study 1. Body mass index affected maternal 17-OHPC concentrations. Cord:maternal 17-OHPC concentration ratios averaged 0.2; 17-OHPC was detectible in cord plasma 44 days after the last maternal injection. CONCLUSION: The apparent half-life of 17-OHPC is long, and pharmacokinetic parameters vary widely between subjects and are affected by maternal body mass index. The drug crosses the placental barrier.