Low-molecular-weight heparins: are they interchangeable?

Unfractionated heparin (UFH) has been used as an antithrombotic agent in the treatment of various clinical entities for over 60 years. Low-molecular-weight heparin (LMWH) com- pounds have gradually replaced UFH for these indications as they have several advantages, including subcutaneous administration and the lack of need for laboratory monitoring. Ever since their introduction, there has been discussion about whether LMWH compounds differ in their efficacy and safety. The best answer is given by direct comparison of two or more preparations; however, such trials are very scarce. Comparison using classical meta-analysis is limited as only a small number of trials with the respective low-molecular-weight heparin compounds are available. The objective of the present analysis has been to use a novel way of plotting the odds ratios of the different studies to compare the efficacy and safety of different LMWH compounds in the initial treatment of patients with venous thromboembolism. Classical meta-analysis revealed reductions in safety and efficacy of 30--40% in favour of LMWHs. Contrasting the log odds ratios of efficacy and safety indicated that there is no conclusive evidence that LMWHs have intrinsic different safety and efficacy profiles.