A federal appeals court on Wednesday revived hundreds of claims by plaintiffs who accused Merck & Co of failing to adequately warn about the risks of thigh bone fractures associated with its osteoporosis drug Fosamax.

The 3rd US Circuit Court of Appeals in Philadelphia said the plaintiffs may proceed to trial and a lower court judge erred in finding their state law claims pre–empted by federal law, based on actions of the US Food and Drug Administration.

Circuit Judge Julio Fuentes said the plaintiffs produced sufficient evidence for a jury to conclude that the FDA would have approved "a properly worded warning about the risk of thigh fractures – or at the very least, to conclude that the odds of FDA rejection were less than highly probable."

Merck and its law firm did not immediately respond to requests for comment. A lawyer for the plaintiffs did not immediately respond to a similar request.

The decision overturned a March 2014 ruling by US District Judge Joel Pisano, who has since retired from the bench. Pisano had ruled that all claims by plaintiffs who were injured prior to Sept. 14, 2010, were pre–empted, leaving only about 20 active cases.

Fosamax has been prescribed to treat or prevent bone loss in post–menopausal women since 1995.

Merck's sales of the drug totaled $3.05 billion in 2007, the last year before the Kenilworth, New Jersey–based company lost patent exclusivity. Fosamax is now available as a generic.

The plaintiffs claimed to suffer thigh fractures stemming from long–term use of Fosamax and said Merck knew about the risk for more than a decade before adding a warning label.

The case is In re: Fosamax (Alendronate Sodium) Products Liability Litigation, 3rd U.S. Circuit Court of Appeals, No. 14–1900.