Pharmaceutical giant Merck & Co. chose to go on the offensive and voluntarily withdraw its arthritis drug Vioxx from the market Thursday. A new study indicated that the drug nearly doubled the risk of heart attacks and strokes among people taking it for at least 18 months or longer. Although the risk was still small (approximately 4%) Merck chose to be proactive and pull the drug. The announcement panicked people who were on the popular pain medication.

'We are taking this action because we believe it best serves the interest of patients,' Merck Chairman Ray V. Gilmartin said. Merck noticed the problems because it was conducting a long-term study on Vioxx for hopes of using it as a drug to slow the growth of colon polyps.

The fallout for Merck will be huge. 84 million prescriptions have been written for Vioxx. The drug, which has been highly promoted, has sold well since its debut in 2001. Worldwide sales have been over $2 billion per year. Merck has also agreed to buy back unused supplies of Vioxx. Doctors across the country reported a rash of calls from patients who were curious about what to do. Vioxx is for people in pain so the problem is particularly acute. Yesterday Merck’s stock plummeted 27% on the news.

The departure of Vioxx also clears the way for rival arthritis drugs such as Pfizer’s Celebrex but may also cause suspicions about drugs of the same class. Merck does have other drugs in the pipeline and awaiting approval that may end up taking the place of Vioxx if they received federal approval. The spotlight is on the FDA and this latest revelation may lead to a longer delay in getting other drugs of the same class to reach the market even if there are no risks associated with them. One of the concerns is that the clinical trials are too short. In the case of Vioxx, problems developed after 18 months of use. Currently the FDA requires trials that range from six months to a year for drugs that treat chronic diseases such as arthritis.

Vioxx is a specific type of medication called a Cox-2 inhibitor. These drugs don’t cause stomach problems like other drugs for pain and inflammation do. Also they are far more expensive and so drug companies have been pushing them to chronic pain sufferers.

Merck’s bad news could continue as patients decide to file lawsuits. There have already been a small number of suits filed that allege Merck made misleading claims about Vioxx and this is only expected to increase. Although it would be hard for lawyers to prove that Vioxx was the sole contributor to a heart attack, eager attorneys are already trolling for patients.