Pfizer has leapt to the defense of its top-selling cholesterol-lowerer Lipitor after lawsuits questioned the safety of the drug following a link to nerve damage and dementia.

Two men filed lawsuits in Manhattan State Supreme Court last week, claiming that Lipitor (atorvastatin) had caused them to experience side effects including memory loss, peripheral neuropathy, fatigue and – in one of the suits - muscle damage.

But Pfizer insisted that there is no evidence to suggest the statin is linked to dementia or peripheral neuropathy, and that all known risks associated with Lipitor have been added to its labelling.

The allegation of muscle damage is sensitive, as concern over the rare muscle reaction known as rhabdomyolysis caused the withdrawal of Bayer’s Lipobay (cerivastatin) from the market and dogged another statin - AstraZeneca’s Crestor (rosuvastatin) - on its way to market. Lipitor’s labelling – in common with all statins – warns patients to tell their doctor if they suffer any symptoms of muscle pain or weakness.

"To create undue concern and doubt about Lipitor is a real disservice to health care professionals who prescribe Lipitor and the patients who depend on Lipitor to reduce heart disease, which is the leading cause of death in the USA and around the world," said Michael Berelowitz, Pfizer Worldwide Medical.

"Pfizer intends to vigorously challenge in court all the baseless claims made in these lawsuits," the group's release said. The company is already defending another of its products, the COX-2 inhibitor Celebrex (celecoxib), against allegations that the drug caused patients to suffer heart attacks and stroke.

The lawsuits were filed by Charles Wilson, 67, who claims to have taken the drug for over a year, and Michael Mazzariello, 47, who says he only took it for two months.

Pfizer said Lipitor is one of the most extensively studied medicines in history, with more than 400 completed and ongoing clinical trials in over 80,000 patients.