Low-molecular-weight heparin (LMWH) is easier to administer than unfractionated heparin because fixed doses can be given without laboratory monitoring. The use of LMWH has permitted home treatment for many patients with deep venous thrombosis. The efficacy of LMWH in pulmonary metabolism has not been clearly documented, but because this condition shares a common pathophysiologic process with deep venous thrombosis, LMWH may prove useful.
Quinlan and associates performed a meta-analysis of randomized studies comparing fixed-dose LMWH with dose-adjusted intravenous unfractionated heparin in the initial treatment of pulmonary embolism. Trials including patients with pulmonary embolism in the context of deep venous thromboembolism with the primary outcome of symptomatic recurrence at end of treatment were included. Other secondary outcomes included recurrence at three months, all-cause mortality, and major or minor bleeding. Twelve studies using six LMWH preparations met the inclusion criteria; most were small trials.
Most study results suggested a decrease in symptomatic events following treatment with LMWH and at three months after conclusion of treatment, compared with unfractionated heparin, whether pulmonary embolism was symptomatic or asymptomatic. All-cause mortality did not differ between the two treatments. The incidence of major bleeding was similar among groups, while minor bleeding was modestly increased in patients who received LMWH. There were no differences among the different LMWH preparations.
The authors conclude that LMWH is as effective as unfractionated heparin in the initial treatment of symptomatic and asymptomatic pulmonary embolism. Safety comparisons are difficult to make because of the low number of outcome events in the studies. The type of LMWH used does not appear to influence efficacy or safety estimates. Outpatient management of non-massive pulmonary embolism may become a reality if more studies confirm the safety of this treatment approach.