Published: August 2009

Combination anticoagulants - increased bleeding risk

Prescriber Update 30(3): 20
August 2009

Medsafe is aware that ACC has recently received a number of claims for treatment injury from patients prescribed a combination of warfarin and aspirin.

The adverse events included major bleeding events such as subdural haematoma and intra-cerebral haemorrhage. Importantly some of these events have occurred in patients with an INR within the therapeutic range who were also taking low dose aspirin (100 mg to 150 mg each day).

Warfarin has been prescribed in these patients for anticoagulation in the presence of atrial fibrillation and in patients with prosthetic heart valves. As prescribers may be aware, anticoagulant combinations are also sometimes used for secondary prevention of ischaemic stroke and myocardial infarction.

For many of the therapeutic indications for warfarin the evidence does not suggest that a combination of aspirin and warfarin is more effective than warfarin alone.1

The literature indicates there is an increased risk of major bleeding events when warfarin and aspirin are used in combination;2 therefore prescribers are reminded to consider these risks before prescribing this combination.

Prescribers are also reminded to ask patients if they are taking aspirin prior to commencing warfarin.

  1. Hurlen M, Abdelnoor M, Smith P et al (2002) Warfarin, Aspirin, or both after myocardial infarction, New England Journal of Medicine, 347 (13):969 – 74.
  2. Shireman T, Howard P, Kresowik T et al (2004) Combined anticoagulant – antiplatelet use and major bleeding events in elderly atrial fibrillation patients Stroke, 35:2362 – 67.