Changes in the pharmacokinetics of the low-molecular-weight heparin enoxaparin sodium during pregnancy

OBJECTIVE: We sought to evaluate the pharmacokinetics of subcutaneously adm inistered enoxaparin sodium during and after pregnancy. STUDY DESIGN: Daily subcutaneous injections of enoxaparin sodium (40 mg) we re administered to 13 pregnant women. On 3 separate occasions, once early i n pregnancy (12-15 weeks), once late in pregnancy (30-33 weeks), and once i n the nonpregnant state (6-8 weeks post partum), serial blood samples were collected, and plasma was analyzed for antifactor Xa activity. Analysis of variance was used for statistical analysis. P < .05 was significant. RESULTS: The time to maximum concentration and the mean residence time in p regnancy compared with the postpartum state were not significantly differen t. During early and late pregnancy, maximum concentration and the last meas urable anti-factor Xa activity level were lower than in the nonpregnant sta te (P < .05). The area under the plasma activity-versus-time curve was sign ificantly lower in pregnancy than in the postpartum state (P < .05). CONCLUSION: The pharmacokinetics of enoxaparin sodium are significantly dif ferent during pregnancy than in the same women when nonpregnant. The observ ed difference is likely because of increased renal clearance of enoxaparin during pregnancy. This finding has significant implications for appropriate dosing of enoxaparin in pregnancy.