Dosing of unfractionated heparin in obese patients with venous thromboembolism.

BACKGROUND: Aggressive weight-based dosing guidelines help achieve prompt therapeutic anticoagulation in patients with venous thromboembolism (VTE). While obese patients with VTE face an increased risk of recurrence, physicians typically resist prescribing doses two to three times the usual dose because of concern about bleeding complications.
OBJECTIVE: To examine the use of unfractionated heparin in obese patients with VTE at an academic teaching hospital in order to document the extent and pattern of underprescribing in this high-risk patient population.
DESIGN: Three-year, cross-sectional consecutive case series. PATIENTS: Adult inpatients with VTE and a body mass index ≥30 kg/m(2) who were treated with unfractionated heparin. MEASUREMENTS: Time to achievement of therapeutic anticoagulation (activated partial thromboplastin time >60 s) and gap between recommended and prescribed heparin doses.
RESULTS: Time to attainment of therapeutic anticoagulation exceeded 24 h in 29% of study patients (n = 84) and exceeded 48 h in 14% of patients. In 75 patients (89%), the prescribed bolus dose fell below the recommended dose of 80 units/kg, and in 64 patients (76%) the initial continuous infusion fell more than 100 units/h below--in some cases more than 1000 units/h below--the recommended dose of 18 units/kg/h. There was a significant correlation between time to therapeutic anticoagulation and initial infusion dose (Spearman r = -0.27; p < 0.02). Each decrease of 1 unit/kg/h translated to a delay ranging from about 0.75 h to 1.5 h over the range of prescribed doses (6 to 22 units/kg/h).
CONCLUSIONS: A substantial proportion of obese patients treated with unfractionated heparin experienced a delay >24 h in achieving adequate anticoagulation, and the vast majority received an inadequate heparin bolus or initial continuous infusion (or both) according to current dosing guidelines.