The US drug giant Merck withdrew Vioxx in September 2004 after evidence linking it to heart attacks and stroke.

Now a US team at Duke University says taking low-dose aspirin alongside Vioxx might prevent these side effects, the journal Cell Metabolism reports.

A Texan court recently found Merck guilty of negligence over its handling of Vioxx, prompting worldwide lawsuits.

Unwanted side effects

COX-2 inhibitors are more "stomach friendly" alternatives to traditional pain relief drugs called non-steroidal anti-inflammatory drugs (NSAIDs), which can sometimes cause side effects such as ulcers and bleeding.

They are used to treat pain and inflammation in arthritis and to relieve acute pain.

Since the heart safety concerns surrounding Vioxx and other COX-2 inhibitors were raised, researchers have been investigating how they might be avoided.

Dr Thomas Coffman, along with colleagues from the University of North Carolina, Pennsylvania University and Durham VA Medical Center, looked at some of the chemical processes that occur in the body in response to COX-2s.

COX-2s and other NSAIDs, including aspirin and ibuprofen, reduce inflammation and pain by blocking the function of enzymes called cyclo-oxygenases.

These enzymes normally produce chemicals called prostaglandins, such as prostacyclin, and thromboxanes.

Prostacylin keeps blood vessels open and prevents clots, while thromboxane constricts vessels and promotes clot formation.

COX-2 inhibitors cause a decline in prostacyclin without any change in thromboxane levels. In comparison, aspirin lowers both thromboxane and prostacyclin.