Pharmacokinetics of 17-hydroxyprogesterone caproate in multifetal gestation

OBJECTIVE: The purpose of this study was to define the pharmacokinetic parameters of 17-hydroxyprogesterone caproate (17-OHPC) in multifetal gestation. STUDY DESIGN: Blood was obtained at 24-28 weeks' gestation and at 32-35 weeks gestation in 97 women with twin and 26 women with triplet gestation who were receiving 17-OHPC. Six of the women with twins had daily blood sampling for 7 days between 24 and 28 weeks' gestation, and pharmacokinetic parameters were estimated with the use of noncompartmental analysis. Modeling was applied to estimate the population parameters and to simulate various treatment scenarios. RESULTS: The apparent half-life of 17-OHPC was 10 days. Body mass index significantly impacted 17-OHPC concentrations, but fetal number and parity did not. Apparent clearance was significantly greater in African American than in white women (P = .025). CONCLUSION: This is the first pharmacokinetic analysis of 17-OHPC in pregnant women. Determination of half-life, covariates that affect plasma 17-OHPC concentrations, and the modeling of drug behavior provide insights into this drug's pharmacologic properties during multifetal pregnancy.