Drug makers Merck and Pharmacia are denying charges that the companies' popular arthritis drugs, Vioxx and Celebrex, may cause serious side effects. Both firms defend the benefits of their products and do not believe that safety tests requested by the American Heart Association, the National Stroke Association and the Arthritis Foundation are necessary. These groups requested further investigation of both Vioxx and Celebrex (known as Cox-2 inhibitors) following the announcement several weeks ago of a link between the medications and heart disease.

A study published in the Journal of the American Medical Association found that the Cox-2 inhibitors may cause blood clots, strokes, and heart attacks. Both Vioxx and Celebrex block the Cox-2 enzyme associated with painful arthritic inflammation. The two renowned cardiologists who conducted the research have demanded that both Merck and Pharmacia investigate the connection more thoroughly.