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Abstracts & commentary
Synopsis: The risk of GI hemorrhage exceeds the benefit of primary prevention of MI, and the risk of hemorrhagic stroke is about the same as the benefit conferred.
Sources: Derry S, Loke YK. BMJ 2000;321:1183-1187; Hebert PR, Hennekens CH. Arch Intern Med 2000;160: 3123-3127.
In the risk of gastrointestinal (gi) hemorrhage associated with aspirin use study, Derry and Loke collected all publications of randomized controlled trials of aspirin used as an antiplatelet agent in order to determine whether the risk of GI hemorrhage associated with aspirin use is reduced when either the dose is reduced and/or a modified sustained release form is used. Twenty-four randomized, controlled trials were included, with 66,000 participants. Eight studies involving 24,954 participants used low dosage aspirin, 50-162.5 mg per day.
Meta-analysis revealed that, overall, GI hemorrhage occurred in 2.47% of patients taking aspirin compared with 1.42% taking placebo. The number of patients need to harm based upon an average of 28 months of aspirin was 106. Analyzing separately the eight trials that used low-dose aspirin did not change the result (2.3% for aspirin compared to 1.4% placebo.)
Hebert and Hennekens note that while numerous randomized, controlled trials document the conclusive benefit of aspirin in preventing secondary cardiovascular events and in modifying evolving myocardial infarction (MI), there has been insufficient evidence to recommend aspirin for primary prevention of MI. To address this question, Hebert and Hennekens collected four randomized, controlled trials (51,000 subjects) of the use of aspirin in primary prevention of occlusive events, one of which included women as well as men. Analysis revealed that the number to treat to prevent one MI was 150. This is also the number to treat with aspirin to cause one hemorrhagic stroke (whether for primary or secondary prevention).
Comment by Michael K. Rees, MD, MPH
Derry and Loke’s study documents that about one in 100 patients taking aspirin over a 28-month period experience GI hemorrhage, which is not reduced by either lowering the dosage of aspirin or using a sustained-relief formulation. Aspirin is known to have a significant benefit in secondary prevention of MI; it estimated that the number to treat to prevent one event is 73. But what about the use of aspirin for primary prevention? Does the benefit conferred by aspirin warrant the risk? This is one of the issues addressed in the paper by Hebert and Hennekens.
Many patients believe that taking a daily aspirin is a benign method of preventing that first MI, but this is far from true. The risk of GI hemorrhage exceeds the benefit of primary prevention of MI, and the risk of hemorrhagic stroke is about the same as the benefit conferred. Hebert and Hennekens conclude: "Whether to recommend aspirin therapy for an individual patient involves assessing the patient’s cardiovascular risk profile and then weighing the clear benefit of reducing the risk of a first MI against the adverse effects of long-term administration." At least for GI bleed, the risk is not reduced by either reducing the dose of aspirin or using a modified delivery system.