Matt Rourke, File, Associated Press
FILE - In this June 14, 2011 file photo, the drug Lipitor is displayed at Medco Health Solutions Inc., in Willingboro, N.J. Lipitor, the best-selling drug ever, was viewed as such an also-ran that it almost didn't make it into patient testing. But Lipitor reigned for nearly a decade as the top-selling drug. It's set to be toppled after getting its first generic rivals four weeks ago.

By LINDA A. JOHNSON

Associated press

TRENTON, N.J. — Sales of Lipitor, the top-selling drug in history, have leveled off after a steep plunge following the start of U.S. generic competition.

New figures from data firm IMS Health show that at the end of December, sales of Pfizer Inc.'s Lipitor were at just above 37 percent market share.

Two new generic versions came on the market at the beginning of December, and in the first full week of the month they had siphoned off a combined 59 percent of sales. By the last week of December, atorvastatin pills from Ranbaxy Laboratories Ltd. and the authorized generic from Watson Pharmaceuticals Inc. only picked up another 4 percent between them.

That's because Pfizer is fighting hard to retain sales, with big discounts to patients and insurers.

Lipitor lost U.S. patent protection on Nov. 30.

Pfizer, the world's largest drugmaker, has been offering patients discount cards that give them a $4 copayment — less than the copay for all but the most popular generics — if they keep taking Lipitor rather than defecting to a cheaper generic version.

New York-based Pfizer also has been giving insurance plans that agree to only cover brand-name Lipitor for the time being the difference between what they had been paying for the brand and what they would pay for cheaper generics.

Until recently, Pfizer has been heavily advertising the copay program, called "Lipitor For You," and still is running some ads. Usually drugmakers end all advertising of brands well before the first generic competition arrives.

But with Lipitor generating about $7.9 billion in annual sales in the U.S. and nearly $11 billion worldwide, Pfizer elected to pull out all the stops to hang onto sales for as long as possible.

The unprecedented strategy, closely watched in the industry, appears to be paying off. Normally, sales of a brand name drug continue to fall over the weeks and months after the start of generic competition.

"It's been pretty stable after the first few weeks," Michael Kleinrock, research director at the IMS Institute for Healthcare Informatics, told The Associated Press, adding, "It's still early days."

Because the arrival of generics brought a chance for health insurers, plan sponsors and patients to save significant money, insurers had prepared long ago to automatically switch all their patients on Lipitor to generics. Pfizer's strategy upended that.

Pfizer spokesman MacKay Jimeson wrote in an email response to questions that "Lipitor continues to meet our expectations.

"Enrollment in the Lipitor For You program has been in line with our expectations, as we expect the majority of patients will be automatically switched to a generic. Nonetheless, our goals are to support patient choice," he said.