Pfizer Inc., the world's largest drugmaker, next month will expand a discount program to allow 43 million uninsured Americans to buy medicines such as its Lipitor cholesterol treatment at a lower price.

Families making less than $45,000 and individuals making less than $31,000 will save an average of 37 percent on Pfizer drugs, the New York company said in a statement. Those with incomes above the thresholds will save about 15 percent.

Drugmakers such as Pfizer are trying to preempt legislation that would set price controls on medicines in the United States and legalize drug imports from Canada, where the government sets prices as much as 70 percent lower than prices in the United States.

Shares of Pfizer fell 15 cents, to $33.72, in New York Stock Exchange composite trading yesterday.

Pfizer, whose drugs include the depression medicine Zoloft and the arthritis treatment Celebrex, will offer the discounts to two-income families, single parents, the self-employed and new college graduates. The cost will be similar to the prices paid by large purchasers, the company said.

Families making less than $31,000 a year or individuals earning less than $19,000 a year can receive free Pfizer medicines from doctors' offices, community health centers and hospitals, the company said. Last year Pfizer provided more than 6.6 million free or discounted prescriptions to more than 1.5 million people in the United States, it said.

Pfizer said it knows of no other program for the uninsured as large as the one it announced today. Some analysts said the program won't be as beneficial as the company says.

"In truth, an insured person can get the drug a lot cheaper, even the HMOs and the group buyers get them a lot cheaper, than what Pfizer is offering the uninsured at 15 percent off," said Girish Tyagi, an analyst with Thomas Weisel Partners in Boston.

The company will be able to assess the impact of the programs on its earnings in about six months, Karen Katen, president of Pfizer's global pharmaceuticals business, said in an interview. The expense is hard to forecast because it depends on the number of people who enroll, she said.

The cost won't "be financially material to the top or bottom line," J. Patrick Kelly, president of Pfizer's U.S. pharmaceuticals business, said in a later televised interview.

Pfizer will use its sales force to inform doctors about the program, Katen said.

Pfizer competitors such as Whitehouse Station, N.J.'s, Merck & Co. and Eli Lilly & Co. of Indianapolis said they already have programs to help people without drug coverage.

Merck gives patients free medicines on a case-by-case basis if they can't afford the product and their doctor asks the company for help.

Lilly offers the uninsured a free three-month supply of medicine under its Lilly Cares program. Unlike its program for seniors, called Lilly Answers, Lilly Cares has no age limits.