Many patients with venous thromboembolism are being treated with low molecular weight
heparin for extended periods of time. It is not certain if it is necessary to assess
anti-Xa levels for extended treatment periods. This study is a prospective assessment
of anti-Xa levels in patients on long-term therapy for acute venous thromboembolism
who have active cancer. Consecutive consenting patients from one center in a multicenter
trial that compared 6 months of low molecular weight heparin with oral anticoagulant
therapy were treated with therapeutic doses of dalteparin (200 IU per kilogram) subcutaneously
daily. Anti-Xa levels were assessed at the end of weeks 1 and 4, 4–6 hours after injection
of dalteparin. Patients were followed for bleeding and recurrent venous thromboembolism.
There were 24 patients who had anti-Xa levels measured at weeks 1 and 4. Two other
patients had week 1 measurements performed but died before the week 4 sample was collected
due to their underlying cancer. The mean anti-Xa levels at weeks 1 and 4 were 1.11
and 1.03 anti-Xa units/ml respectively (P=0.13). These results suggest that for patients
with active cancer receiving extended duration therapy with low molecular weight heparin
(dalteparin) there is no accumulation of anti-Xa effect over the first month of therapy.
Monitoring of anti-Xa levels in this situation is usually not required.
Keywords
Low molecular weight heparin - anti-Xa levels - VTE - cancer
