Serebruany VL: The risk of bleeding complications after different doses of aspirin (ASA): A post-hoc analysis of 192,036patients enrolled in 31 randomized controlled trials (Abstract P3506) A meta-analysis of 31 randomized trials enrolling 192,000 patients was performed to examine the effect of aspirin doses on bleeding. It was found that low daily doses (equivalent to 81 mg in the U.S.) were remarkably safer than higher ones (above 200 mg), particularly in terms of gastrointestinal (GI) bleeding. Victor L. Serebruany, MD, PhD, from the Sinai Center for Thrombosis Research at Johns Hopkins University in Baltimore, concluded that low daily doses of aspirin were associated with the lowest risk. Doses of 81 mg caused fewer major bleeding events, particularly GI bleeding, than did doses of 325 mg.
Patients taking low-dose aspirin reported bleeding complications only 3.26% of the time. By contrast, 11.31% of patients taking moderate-dose aspirin (100-200 mg) experienced bleeding, as did 9.4% of those taking high-dose aspirin (more than 200 mg).
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Fondaparinux and Enoxaparin
Yusuf S: Efficacy and safety of fondaparinux compared to enoxa-parin in 20,000 high-risk patients with acute coronary syndrome without ST elevation: The OASIS 5 Michelangelo Programme (Abstract 1332) OASIS 5/Michelangelo, the largest trial of acute coronary syndrome on record, compared two low-molecular-weight heparins (LMWHs): fondaparinux (Arixtra®, GlaxoSmithKline), and enoxaparin (Lovenox®, Sanofi-Aventis). Both drugs offer an advantage over unfractionated heparin (UFH) in not requiring inconvenient, expensive monitoring of activated clotting time.
In earlier comparisons, fondaparinux had prevented deep vein thrombosis more successfully than enoxaparin. In this study, conducted by professor Salim Yusuf, MD, at McMaster University in Hamilton in Ontario, Canada, investigators were looking for non-inferiority for the newer agent (fondaparinux) in efficacy (rates of combined death, MI, and refractory ischemia at nine days), and at the safety endpoint of major bleeding.
In the OASIS 5 trial, about 70% of patients had indicators of a damaged myocardium, such as elevated troponin T or crea-tine kinase isoenzyme with muscle and brain subunits (CKMB) above the upper limit of normal; in approximately 80% of the patients, their electrocardiograms suggested ischemia. Patients received either fondaparinux 2.5 mg once daily or enoxaparin 1 mg/kg twice daily.
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Efficacy for the two agents was nearly equivalent at nine days. The hazard ratio (HR) for fondaparinux was 1.01 (for non-inferiority, P = .0068). Major bleeding, however, was significantly lower with fondaparinux (HR 0.53; P << .00001). Total bleeding episodes, major bleeding, TIMI major bleeding, and minor bleeding all favored fondaparinux (P << .0001). Significant efficacy advantages for fondaparinux were seen at 30 days (for death, P = .022; for death, MI, and stroke, P = .031). At six months, the additional advantages of fondaparinux in preventing stroke, death, and MI became evident.
Dr. Yusuf concluded that fondaparinux was “non-inferior,” compared with enoxaparin at nine days, conferring substantially lower rates of important bleeding episodes. He noted that consistent results were observed in those undergoing a percutaneous coronary intervention (PCI), such as stenting, and in every other subgroup examined. He added that OASIS 5 clearly showed fondaparinux to be the preferred anticoagulant for patients with acute coronary syndrome.
The Society’s format for major sessions, such as the “Hot Line” presentations, dictated that results be followed with comment by an official “discussant” who was well versed in the clinical arena of the trial presented. With OASIS 5, the discussant, Professor Robert Califf, MD, of Duke University in Durham, North Carolina, was less convinced than Dr. Yusuf of fondaparinux’s superiority. Although he stated unequivocally that OASIS 5 had shown fondaparinux to be an “excellent” regimen for anticoagulation in acute coronary syndrome, he indicated that it was not clear whether the bleeding difference was a result of “intrinsic differences in physical properties of comparative drugs or better dosing with fondaparinux.”
Results of the clinical trial SYNERGY (Superior Yield of the New Strategy of Enoxaparin, Revascularization, and Glycoprotein Ilb/IIIa Inhibitors), which became available during the OASIS 5 trial, demonstrated that patients receiving enoxa-parin for acute coronary syndrome and UFH when they underwent catheterization for a PCI had multiple bleeding risks. SYNERGY was a prospective, randomized, open-label, multi-center trial involving high-risk patients with acute coronary syndromes. The OASIS 5 regimen required that patients receive UFH during catheterization. Patients with impaired renal function also had greater bleeding risk with enoxaparin.
Dr. Califf stated:
Enoxaparin was disadvantaged by cath lab switching and probably wrong dosing in patients with creatinine clearance of 30-60 ml/minute. . . . Switching to UFH in the cath lab, as was recommended in OASIS 5, is not a recommendation that should be adhered to in this day and time.
Dr. Califf also noted that worse longer-term outcomes of patients with serious bleeding open the possibility that transfusions, rather than the bleeding itself, might confer the added risk.