Pharmaceutical company Merck has pulled its arthritis drug Vioxx off the market because it increases the risk of heart attack and stroke, a move that sent its shares plunging, erasing $25 billion of its market value.
Vioxx, used by two million people around the world, including in Ireland, accounts for 10 per cent of Merck's annual sales.
The withdrawal of the drug casts a cloud over an entire class of widely-used arthritis and pain drugs known as COX-2 inhibitors. "This has implications for all members of this class," said Dr Garret FitzGerald, chairman of the Department of Pharmacology at the University of Pennsylvania.
Merck said that in a colon cancer trial, patients who took Vioxx for three years faced twice the risk of cardiovascular events, such as heart attack and stroke, as patients taking a placebo.
"Patients who are currently taking Vioxx should contact their health care providers to discuss discontinuing use of Vioxx and possible alternative treatments," it said.
Concerns over the drug's side effects have been building in recent years after several studies showed risks attached to it.
Other drugs in the same class, including Pfizer Inc.'s Celebrex and Bextra and Novartis AG's Prexige, have so far not shown the same dangers.
However, the US Food and Drug Administration said it would closely watch other such drugs.
Worldwide sales of Vioxx totaled $2.55 billion last year. Since its introduction in 1999, 84 million people have used the medication. In the United States alone, 91 million Vioxx prescriptions have been written. The drug is sold in some countries under the name Ceoxx. It is believed thousands of Irish patients take the drug.