Scientists wary of Vioxx effects

Vioxx, an anti-inflammatory drug, may cause heart attacks and strokes because of its blood-clotting properties, British scientists say. 

These particular class of drugs drugs, called COX-2 inhibitors, are primarily used to treat pain caused by conditions such as arthritis. They work by blocking the COX-2 enzyme, which is expressed at the particular sites of inflammation and underlies the production of hormones called prostaglandins, which in turn, swell the joints and cause the feeling of pain.

The team reported in the December issue of the Federation of American Societies for Experimental Biology (FASEB) journal that these medications also block the COX-1 enzyme which lines blood vessels.

Vioxx was pulled from shelves in 2004 because of the health risks associated with its use. However, other COX-2 inhibitors such as Celebrex remain on the market, but now carry  a strong warning about the possible side-effects.

Prof. Jane Mitchell from the National Heart and Lung Institute at Imperial College London and her colleagues found that if COX-1 is blocked, blood may clot, which consequently increases the risk of heart attack or stroke if the drugs are taken regularly.

"Our new research is exciting because it means we can work on developing better COX-2 inhibitors that don't pose the same risks in terms of heart attacks and strokes," Mitchell said.

Previously, scientists thought the side-effects of COX-2 inhibitors were tied to blocking the enzyme in the endothelium, which lines blood vessels.  However, Mitchell's team found no evidence of COX-2 in the endothelium. The researchers said the side-effect was on COX-1 in endothelial cells but not other areas, such as platelets.

The study was based on an analysis of human blood vessels, blood and cells.

The research was funded by the British Heart Foundation, the Spanish government and a grant from the European Community.