NEW YORK (CNNMoney.com) - A New Jersey appeals court Friday upheld a class-action lawsuit against Merck from some plaintiffs alleging they were misled regarding the risks of the painkiller Vioxx.

The appellate court ruled that Judge Carol Higbee of New Jersey Supreme Court was proper in certifying a nationwide class. The class action suit was filed by private insurers and HMOs, and is separate from the nearly 10,000 lawsuits filed by patients, or families of patients, who took the painkiller Vioxx.

Merck's lawyers vowed to appeal.

"We believe strongly that each of these companies made its own decision," said Ted Mayer, national outside counsel for Merck. "We will be filing petitions to appeal to New Jersey Supreme Court."

Higbee is overseeing the thousands of lawsuits filed against Merck in its home state of New Jersey.

Merck (down $0.40 to $35.21, Research), the second-biggest U.S. drug maker with $22 billion in 2005 sales, is based in Whitehouse Station, N.J.

Vioxx, an inflammatory treatment for arthritis, was pulled from the market in 2004 after studies showed the drug increased the risk of heart attack and stroke in patients taking it for 18 months.

Chris Seeger, one of the plaintiff lawyers involved in the class-action suit, was not immediately available for comment.

To read about the current case in New Jersey, click here.