The Texas attorney general said on Thursday he has sued Merck & Co., accusing the drugmaker of committing Medicaid fraud in promoting its arthritis drug Vioxx, adding the state of Texas to the thousands of plaintiffs suing Merck over its withdrawn drug.

Texas Attorney General Greg Abbott is seeking $168 million in damages - triple the amount he figures the Texas Medicaid program paid in reimbursements to pharmacists for Vioxx prescriptions filled in the state over a five-year period.

Merck pulled Vioxx from the market last September after a study showed that long-term use of the once $2.5 billion-a-year drug increased the risk of Heart attack and Stroke. Lawsuits have since alleged that Merck knew of the dangers of Vioxx years before it withdrew the painkiller.

As of June 15, Merck said it was facing more than 3,800 product liability suits in state and federal courts, with at least 118 class action suits pending from patients charging that they were harmed by the drug.

Merck has contended all along that it voluntarily withdrew Vioxx as soon as it had definitive evidence of increased risk.

Abbott is the first state attorney general to sue Merck over Vioxx, Merck said.

Industry analysts have predicted that Merck will have to spend billions of dollars on Vioxx litigation.

According to the latest lawsuit, Abbott charges that Merck’s failure to disclose the adverse effects of Vioxx, while offering it to the state’s Medicaid program as a safe painkiller, directly violates the Texas Medicaid Fraud Prevention Act.

Abbott contends that had the facts about Vioxx come to light earlier, doctors and Medicaid patients would have chosen other painkillers, such as generic naproxen, at a fraction of the cost of Vioxx.

The drugmaker said it will vigorously defend itself against the lawsuit brought by the Texas attorney general.

“Merck acted responsibly from researching Vioxx prior to approval in studies with almost 10,000 patients to monitoring the medicine while it was on the market to voluntarily withdrawing the medicine when it did,” the drugmaker said in a statement.