title: A case series of LMWH use in pregnancy: should trough anti-Xa levels guide dosing?
abstract: BACKGROUND
  Pregnancy is a thrombogenic state, increasing the risk for venous thromboembolism (VTE), and the risk of valve thrombosis amongst women with mechanical heart valves (MHV). While low molecular weight heparins (LMWH) are generally dosed based on weight (i.e., enoxaparin 1 mg/kg every 12 hours), data in pregnant women have shown that weight-based dosing does not consistently achieve target anti-Xa levels. In women with MHV, our practice includes titrating LMWH doses to target both trough and peak anti-Xa levels, while for those with VTE peak anti-Xa levels guide dosing.
  
  
  METHODS
  This retrospective case series included pregnant women requiring LMWH treatment doses with at least 3 peak (+/-trough) anti-Xa levels. Our primary objective was to describe the actual LMWH dose required to achieve targeted anti-Xa levels relative to weight-based dosing in patients with MHV. Secondarily, we compared the same for VTE patients; compared actual dosing between those with MHV and VTE; and examined maternal and fetal outcomes.
  
  
  CONCLUSIONS
  Women with MHV (N=4) required greater than weight-based dosing of enoxaparin (1.35 mg/kg Q12H) to achieve targeted anti-Xa levels. Importantly, achieving target peak anti-Xa levels did not always ensure maintenance of minimum trough levels. VTE patients (N=12) did not require more enoxaparin (0.96 mg/kg Q12H) than weight based dosing. MHV patients received more enoxaparin compared to VTE patients (P<0.001). No bleeding or clotting complications were associated with LMWH administration. In pregnant women with MHV at high risk of thromboembolism, LMWH dosing guided by trough and peak anti-Xa levels should be considered.
authors.affiliation: Alberta Health Services, Edmonton, Alberta, Canada.
authors.forename: Michelle
authors.initials: M
authors.lastname: Berresheim
authors.affiliation: Alberta Health Services, Edmonton, Alberta, Canada.
authors.forename: Jodi
authors.initials: J
authors.lastname: Wilkie
authors.affiliation: Department of Medicine, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Kara A
authors.initials: KA
authors.lastname: Nerenberg
authors.affiliation: University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Quazi
authors.initials: Q
authors.lastname: Ibrahim
authors.affiliation: University of Alberta, Edmonton, Alberta, Canada. Electronic address: tammy.bungard@ualberta.ca.
authors.forename: Tammy J
authors.initials: TJ
authors.lastname: Bungard
mesh_terms: D000284:Administration, Oral; D000293:Adolescent; D000328:Adult; D000925:Anticoagulants / Q000008:administration & dosage; D015415:Biomarkers / Q000097:blood; D004305:Dose-Response Relationship, Drug; D065427:Factor Xa Inhibitors / Q000097:blood*; D005260:Female; D006495:Heparin, Low-Molecular-Weight / Q000008:administration & dosage*; D006801:Humans; D008875:Middle Aged; D011247:Pregnancy; D011249:Pregnancy Complications, Cardiovascular / Q000097:blood* / Q000175:diagnosis / Q000188:drug therapy*; D011256:Pregnancy Outcome; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D016896:Treatment Outcome; D054556:Venous Thromboembolism / Q000097:blood* / Q000175:diagnosis / Q000188:drug therapy*; D055815:Young Adult
chemical_list: D000925:Anticoagulants; D015415:Biomarkers; D065427:Factor Xa Inhibitors; D006495:Heparin, Low-Molecular-Weight
keywords: Anti-Xa level; Low molecular weight heparin; Mechanical prosthetic valve; Pregnancy; Thrombosis; Venous thromboembolism