Analysis of unfractionated heparin dose requirements to target therapeutic anti-Xa intensity during pregnancy.
BACKGROUND
Unfractionated heparin (UFH) does not cross the placenta and has demonstrated utility in the prevention and treatment of thrombosis during pregnancy. Limited information is available to guide initiation and monitoring of therapeutic UFH targeting an anti-Xa concentration of 0.3-0.7 u/ml during pregnancy. The objective of this study was to describe UFH doses and monitoring strategies required to achieve and maintain therapeutic anti-Xa intensity in a cohort of women treated with UFH during pregnancy.


METHODS
Patients prescribed anti-Xa adjusted UFH during pregnancies occurring between January 1998 and March 2005 were included.


RESULTS
A total of 39 pregnancies for 37 women were identified. Unfractionated heparin doses were titrated to achieve a mid-interval anti-Xa level of 0.3-0.7 u/ml. Patients required a median 6.5 days and a mean UFH dose of 403.5 u/kg/day to achieve therapeutic anti-Xa levels. Most anti-Xa levels were within the target range (59%). The final UFH dose/kg required at the end of pregnancy was similar to that at the first therapeutic level (P>0.05); however some patients did require dose modification. Patients required a mean 14.1 anti-Xa determinations and 4.6 dose modifications during a mean 23.9 weeks of antenatal UFH therapy. Patient weight and UFH dose at the first therapeutic anti-Xa level were correlated (r=0.383, P=0.018).


CONCLUSIONS
Pregnant women required a mean UFH dose of 403.5 u/kg/day to achieve midinterval anti-Xa levels of 0.3-0.7 u/ml. The required dose was correlated with patient weight and most anti-Xa measurements were within the target range.
Clark
Nathan P
NP
Clinical Pharmacy Anticoagulation Service, Kaiser Permanente Colorado, 280 Exempla Circle, Lafayette, Colorado, USA. nathan.clark@kp.org
Delate
Thomas
T
Cleary
Steven J
SJ
Witt
Daniel M
DM
D000328:Adult; D000925:Anticoagulants / Q000008:administration & dosage; D004305:Dose-Response Relationship, Drug; D016503:Drug Delivery Systems / Q000379:methods; D016903:Drug Monitoring / Q000379:methods*; D015951:Factor Xa / Q000032:analysis; D065427:Factor Xa Inhibitors; D005260:Female; D006493:Heparin / Q000008:administration & dosage*; D006801:Humans; D011247:Pregnancy / Q000097:blood* / Q000187:drug effects*; D011249:Pregnancy Complications, Cardiovascular / Q000097:blood* / Q000517:prevention & control; D012189:Retrospective Studies; D013927:Thrombosis / Q000097:blood* / Q000517:prevention & control; D016896:Treatment Outcome
D000925:Anticoagulants; D065427:Factor Xa Inhibitors; D006493:Heparin; D015951:Factor Xa