BERKELEY, CA (UroToday.com) - Patients on warfarin therapy are frequently switched to low-molecular-weight heparin before surgery as part of "bridging therapy".

In the February 6th issue of Annals of Internal Medicine, O'Donnell and colleagues performed a prospective study evaluating the preoperative anticoagulant activity of LMWH in patients undergoing bridging therapy from warfarin to LMWH before surgery.

A total of 94 patients who were switched from warfarin to enoxaparin 5-7 days before surgery constituted the cohort of the study. Enoxaparin was administered at a dose of 1mg/kg twice daily and was stopped the night before surgery. Blood heparin level was measured in 80 patients as anti-factor Xa activity an average of 14 hours before surgery.

The average anti-Xa heparin level was 0.6 U/mL. The anti-Xa heparin level, measured before surgery, was 0.5 U/mL or greater in 54 (68%) patients and 1.0 U/mL or greater in 13 (16%) patients. Elevated anti-Xa heparin levels were associated with a short interval from the last dose and with obesity.

These data suggest that two-thirds of patients who received standard bridging therapy with LMWH continued to exhibit significant levels of anticoagulation after stopping enoxaparin an average of 14 hours before surgery. The authors recommend giving the last LMWH dose the morning of the day before surgery in preoperative patients. The impact of this recommendation on the incidence of venous thromboembolism was not studied.

Martin J. O'Donnell, MB; Clive Kearon, MB, PhD; Judy Johnson, RN; Marlene Robinson, RN, BScN; Michelle Zondag, RN; Irene Turpie, MB, MSc; and Alexander G. Turpie, MB

Ann Intern Med.2007; 146: 184-187

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Written by Ricardo Sånchez-Ortiz, MD, a Contributing Editor with UroToday.

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