ATLANTA — Comparisons between enoxaparin and fondaparinux were perhaps inevitable when findings from two major clinical trials that evaluated the two different antithrombotic drugs as adjuncts to fibrinolytic therapy for acute MI were reported back-to-back at the annual meeting of the American College of Cardiology.
Such comparisons are also dangerous, cautioned many experts, who noted that across-study comparisons are notoriously untrustworthy.
Nonetheless, the two lead investigators for the studies gave their individual takes on the pros and cons of the drugs, which both met their primary efficacy end points of proven superiority to the standard antithrombotic drug, unfractionated heparin (UFH).
The biggest selling point for fondaparinux was safety, with a significantly reduced rate of major bleeding events, compared with UFH, in the Organization to Assess Strategies for Ischemic Syndromes (OASIS) 6 trial, said Dr. Salim Yusuf, professor of medicine at McMaster University, Hamilton, Ont.
The biggest problem with fondaparinux seemed to be its lack of improved efficacy in patients who underwent a primary percutaneous coronary intervention (PCI), the preferred mode for treating MIs in the United States.
In fact, a detailed analysis suggested that treatment with fondaparinux showed a trend toward inferior outcomes during the first 3 days after PCI, then seemed to become more beneficial during continued treatment.
That raised the possibility that in the PCI setting, the best approach might be to use UFH or a similar drug first and then switch to fondaparinux, a strategy that will need testing in a new study, Dr. Yusuf said.
Enoxaparin's profile was almost a mirror image of that of fondaparinux, in that its Achilles' heel was safety, causing 50% more major bleeds than UFH. But the advantage of low-molecular-weight heparin is versatility, with no apparent downside in patients undergoing PCI. Although no patients in the new enoxaparin study were treated with primary PCI, the drug was used for rescue PCI without problems, and its efficacy in primary PCI was proved in an earlier study, said Dr. Elliott M. Antman, director of the cardiac unit at Brigham and Women's Hospital, Boston.
“You can take enoxaparin to the cath lab without having to switch drugs, and we know it's when you cross from one antithrombin to another that you run into bleeding concerns,” Dr. Antman said.