NEW YORK (CNNMoney.com) - Lipitor, the world's top-selling drug from the world's leading pharmaceutical company, has been targeted by two lawsuits blaming it for memory loss and damage to the nervous system.

The plaintiffs also have accused Pfizer (down $0.49 to $23.42, Research), maker of the cholesterol-cutting drug, of having "failed to inform consumers and the medical profession of serious side effects associated with the statin Lipitor," according to a statement from plaintiff lawyer Mark Krum.

Plaintiffs Charles Wilson, 60, a former insurance executive from Atlanta, and Michael Mazzariello, 47, an attorney from New York, filed the lawsuits Wednesday night in New York State Supreme Court.

Wilson took Lipitor for 17 months from 2002 to 2003 and blames the drug for memory loss, nervous-system damage, and weakness in his arms and legs, which caused him to leave his job, according to Krum. Mazzariello blames Lipitor for memory loss and muscle damage, said Krum, and he needs a cane to walk.

Pfizer spokesman Bryant Haskins insisted that Lipitor is safe, effective and well-studied, and said the lawsuits have no scientific basis. He also denied allegations that Pfizer withheld information about the drug.

"I assure you that we will vigorously challenge in court all the baseless claims made in these lawsuits," said Haskins. "To create any undue concern about Lipitor is a real disservice to the millions of patients who depend on the product to reduce their risk of heart disease, which is the leading cause of death in the United States."

Haskins said Lipitor's safety record is backed by its use by 18 million patients, and more than 400 ongoing or completed clinical trials involving more than 80,000 patients worldwide.

News of the lawsuits "won't help Lipitor sales," regardless of their merit, said Les Funtleyder, analyst for Miller Tabak.

"If the story starts to get out, physicians will be hesitant to prescribe it because of malpractice suit [fears]," said Funtleyder. "Regardless of whether it's real, it will start to raise questions in people's minds."

On the other hand, Funtleyder thinks doctors should be able to tell whether the allegations are valid, or completely off base.

"Lipitor is a widely prescribed drug and physicians have a lot of experience with it," said Funtleyder. "If [these allegations] are not consistent with their experience, they will consider this a frivolous lawsuit. You would think that given the absolute size of Lipitor [sales], that if there were common severe side effects, they would have showed up."

Lipitor sales totaled $12.2 billion in 2005, the record for any drug. Pfizer, based in New York, is the world's biggest drug company, with $51.3 billion in sales last year.

However, the 3 percent growth for Lipitor sales in the first quarter of this year was "slower than anticipated," according to the company. Nonetheless, chief executive officer Henry McKinnell has stuck to his sales goal of $13 billion for 2006.

But some analysts are concerned that Lipitor sales could get squeezed this year by a generic version of Merck's (down $0.23 to $33.73, Research) cholesterol-cutting Zocor. Merck's top-seller totaled $4.4 billion in sales last year, but its patent protection expires June 23. When a branded drug becomes a generic, the price typically plunges 80 percent over the next year, encouraging customers to switch drugs.

Jon LeCroy, analyst for Natexis Bleichroeder, said the specter of a generic Zocor dwarfs any trouble Pfizer might have from a "random lawsuit."

"We haven't seen [the alleged side effects] in large-scale clinical trials of Lipitor and we haven't heard of that being a problem," said LeCroy. "Unless we see a bigger problem, I doubt it will be an issue for them. A much bigger issue is Zocor becoming generic at the end of the month."

Though Lipitor and Zocor are both cholesterol-cutting drugs, Pfizer is working hard to differentiate the two as separate products. Pfizer is testing Lipitor, which lowers LDL or "bad" cholesterol, in conjunction with the experimental drug torcetrapib, which increases HDL or "good" cholesterol. Al Rauch, an analyst for A.G. Edwards, has projected that a successful Lipitor-torcetrapib combination could add $8 billion in annual sales for Pfizer.

The analysts interviewed for this story do not own Pfizer stock.

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