Previous federal diet-drug cases were consolidated into a class action against Wyeth at the U.S. District Court in the Eastern District of Pennsylvania in 1997, and the court approved a nationwide class-action settlement in 2000. Wyeth has taken $16.6 billion in charges for the cases, according to its most recent annual report, but because some potential plaintiffs opted out of the class action, Wyeth and other companies, including Indevus, may still be on the hook.

In its filings with the U.S. Securities and Exchange Commission, Wyeth noted that it has set aside about $3.5 billion in reserve to handle remaining diet-drug legal claims.

Indevus has been named as the primary defendant in the new federal cases, which were all transferred from Middlesex Superior Court in Cambridge at the request of Madison, N.J.-based Wyeth, which is one of the other defendants. Indevus now specializes in buying drug rights from other pharmaceutical developers, but according to the court papers, Indevus' predecessor company had been involved in developing the diet drug Redux, which Wyeth's predecessor manufactured.

Another defendant in the cases, Boehreinger Ingelheim Pharmaceuticals Inc. of Ridgefield, Conn., was also involved in making the drugs.

Other related cases pending at the state court level appeared before Associate Justice Raymond Brassard this week for a hearing about the statute of limitations in the case. As of Wednesday, Brassard had not issued a ruling.

All told, Boston-based law firm Sugarman, Rogers, Barshak & Cohen PC is representing about 1,600 plaintiffs in the new round of cases, said attorney Edward Barshak. Barshak said Massachusetts has a "well-established discovery rule in personal-injury cases."

"The issue before the judge is whether these plaintiffs knew, or should have known, of their injuries and where it came from within three years of (them) bringing suit," Barshak said.

Wyeth is covering Indevus' defense costs for the diet-drug cases, an arrangement that the two companies entered into some time after 2000, said Indevus attorney Barbara Wrubel, a partner in the New York office of Skadden, Arps, Slate, Meagher & Flom LLP.

"Over all these many years, (Indevus) has never been taken to trial or had any judgments entered against it," Wrubel said. "The real focus has been Wyeth."

Wyeth did not respond to requests for interviews.

In its court documents, Wyeth said the plaintiffs bar is trying to "funnel plaintiffs from around the country to Middlesex County. ... Plaintiffs proffer no legitimate reason for why they would bring suit in a jurisdiction as distant as 3,000 miles from their homes."

When asked about the residency of the plaintiffs, Barshak said the location of the defendant -- in this case Indevus -- is the issue.

"A primary defendant is here in Massachusetts," Barshak said.

In their court filings, the plaintiffs each claim hospital expenses of about $10,000 to date, plus an unknown amount of lost wages and an estimated $250,000 in future medical and hospital expenses for heart-valve disease, heart-valve regurgitation and pulmonary hypertension related to their use of Redux. Their legal claims against Indevus and the other parties include defective design, failure to warn, negligence, fraudulent and negligent misrepresentation and unfair and deceptive practices. The plaintiffs are seeking double or triple damages.

Local litigator Thomas E. Peisch of Conn Kavanaugh Rosenthal Peisch & Ford LLP said the purpose of settling national class-action cases and having them assigned to one court is to "ensure uniformity and finality." In exchange for fairly significant payments, defendants usually get closure, Peisch said.

But sometimes liability lingers on.

"This is one of the weaknesses of our civil justice system," Peisch said. "Claims of borderline merit against borderline entities too often survive and constitute to be a distraction long after they should."