Wyeth agreed to revise a U.S. class-action settlement that could speed resolution of thousands of pending diet-drug claims against the company and bring years of litigation closer to an end.

Under the deal, the pharmaceuticals company would make available $1.28 billion to fund payments to people with heart-valve damage who agreed to participate in the modified version of a U.S. settlement dating back to 1999. The revision changes the way payments are calculated. Under the previous version of the settlement, latecomers risked getting nothing.

The claims allege heart-valve damage from Wyeth's diet drugs Redux and Pondimin, which were one-half of the combination known popularly as fen-phen. The drugs were taken off the market in 1997.

Under the revised pact, individual payouts would be less than under the previous agreement, and also would depend on medical condition, age and duration of drug use. But the revision has two selling points for plaintiffs: It is expected to both expedite payments and, for people with proven heart damage, guarantee compensation.

In agreeing to the revision, Wyeth, for its part, reduces uncertainties over a large swath of its legal liabilities, including nearly 40,000 current claims and as many as 100,000 people who may become eligible for claims in the future, the company said.

Wyeth has set aside nearly $17 billion to cover its fen-phen legal costs and liabilities from settlements and cases decided at trial. About $3 billion remains, and the $1.28 billion for the revised settlement could come from that pot. Nearly six million people took the drugs while they were on the market.

"Plaintiffs get a guaranteed recovery, if they pass a medical review," said Wayne Spivey, a Philadelphia lawyer representing more than 10,000 claimants. Mr. Spivey supported the change and negotiated for it as part of a consortium of plaintiffs' lawyers. The previous settlement featured a fixed schedule of payments and a finite pot of money. "The biggest risk was there wasn't close to being sufficient money in the national settlement trust to pay legitimate claimants," Mr. Spivey said.

If approved by a federal judge later this month, the revision would bring Wyeth much closer to halting the financial drain of litigation over the diet drugs. The amended settlement also illustrates how a drug maker can endure an onslaught of liability cases. Wyeth's survival suggests there may be a path, though a long and difficult one, for Merck & Co. and Pfizer Inc. to defend themselves against liability claims involving their Cox-2 painkillers.

The amended Wyeth settlement "will provide a substantial degree of certainty for the company as well as for class members," said Douglas Dworkin, a senior lawyer at Wyeth, based in Madison, N.J. The revision has been in the works since last year, and Wyeth had until Saturday to accept it or walk away. The company decided to go with it, in large part, because more than 95% of affected class members agreed to participate in the modified approach.

The latest change is the seventh amendment to the negotiated settlement. It stands apart from the others because it could bring a quick resolution to the majority of outstanding settlement claims against the company. The change also could hasten settlement negotiations with lawyers representing thousands of people who have opted to take their cases to court.

Besides requiring approval from a federal judge in Philadelphia overseeing the settlement, dissident plaintiffs could appeal the change to block it. Approval is expected and any appeal is unlikely to derail the pact, Wyeth and Mr. Spivey said.

Wyeth has warned that further reserves, beyond the $17 billion, are possible. The company is expected to provide an update later this month.