Auckland researchers have developed a tool to make aspirin safer and more targeted in patients, potentially saving lives.

Thousands of New Zealanders take aspirin to reduce their risk of heart disease and stroke, but the drug's blood-thinning action carries a potentially fatal risk of causing internal bleeding.

The risk varies between patients and, until now, doctors had no objective way of assessing an individual patient's risk.

Researchers from the University of Auckland's Faculty of Medical and Health Sciences and Middlemore Hospital have developed bleeding-risk models, which provide a personalised estimate of a patient's risk of a major bleed.

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The research, published in the journal Annals of Internal Medicine, can be used by doctors with their patients to predict the bleed risk if they were to start taking aspirin.

Lead author Dr Vanessa Selak, a senior lecturer at the University of Auckland, said it was mostly aimed at those who had not had a heart attack or stroke, but were at high risk and thinking about using aspirin.

University of Auckland's Dr Vanessa Selak, the lead researcher in developing a tool to make aspirin a safer and better-targeted preventative for heart disease and stroke. Photo / Supplied
University of Auckland's Dr Vanessa Selak, the lead researcher in developing a tool to make aspirin a safer and better-targeted preventative for heart disease and stroke. Photo / Supplied

"For people who have already had a heart attack or stroke, the benefit of aspirin in reducing cardiovascular disease generally outweighs its harms in increasing bleeding.

"However, guidelines are unclear in people who are at high risk of having their first heart attack or stroke.

"There is a lot of confusion about who should take it, so it is likely that some people are receiving aspirin when they shouldn't be and others are not receiving it when they could potentially benefit from it."

To identify the extra bleed risk from aspirin, the researchers worked out a baseline risk of major bleeds - those that resulted in hospitalisation or death - in people at high risk of cardiovascular disease who were not already taking aspirin.

Researchers analysed anonymous Ministry of Health data from more than 350,000 such people aged 30 to 79 who had seen their GP or practice nurse for a cardiovascular disease risk assessment between 2002 and 2015.

Researchers discovered this original pool of people went on to have 4442 major bleeds, of which 313 (seven per cent) were fatal.

Risk factors for both cardiovascular disease and major bleeds included older age, smoking, diabetes, ethnicity, deprivation and use of blood pressure-lowering medication.

Risk factors only for bleeds included a history of cancer, bleeding, peptic ulcer disease or alcohol-related conditions, or the use of corticosteroids or SSRI antidepressants.

Selak said the next step was to make the research more accessible for doctors to use with their patients, which could be in the form of an app.

The aspirin benefit-harm calculator – likely to be a world-first – could be available by the end of the year.

The research was funded by the Health Research Council.