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A new Auckland study has shown that aspirin's blood-thinning ability is inhibited by some anti-inflammatory painkillers.
Many thousands of New Zealanders take aspirin to reduce their risk of having a heart attack or stroke. Those also taking non-steroidal anti-inflammatory drugs (NSAIDs) that performed poorly in the study are potentially increasing their risk.
Aspirin is one of the most commonly prescribed drugs. It reduces the platelet aggregation - the blood's stickiness - in most people.
The study of 24 people - whose first author is Dr Patrick Gladding, a research fellow at Auckland City Hospital's Green Lane Cardiovascular Service - found that naproxen, ibuprofen, indomethacin and tiaprofenic acid blocked aspirin.
It is the first study to find the effect with naproxen and tiaprofenic acid.
Celebrex and sulindac did not block aspirin, and of the six non-steroidals tested may be the drugs of choice for patients requiring aspirin and NSAIDs, says the study, published on-line in the American Journal of Cardiology.
Dr Gladding said United States medicine regulators had placed a warning on ibuprofen packaging in 2006 warning of the interaction.
His supervisor for the study, cardiologist Dr Mark Webster, said yesterday the study's main message was that if patients took aspirin to reduce the risk of stroke and heart attack, and an NSAID, they should take the latter just once a day and about 30 minutes to an hour after the aspirin.
"The other message is for prescribers to be aware of the interaction and accept that non-steroidals are probably not without some cardiovascular risk in general."
Dr Stewart Jessamine, the senior medical adviser of state medicines regulator Medsafe, is aware of earlier research on the interaction between aspirin and NSAID but has not yet seen the new Auckland study.
"We'll look at it to determine if it needs to go to the Medicines Adverse Reactions Committee to see whether there is any advice that needs to be issued around taking aspirin and these medicines together."
